ANTI-BACTERIAL PACKAGING

Abstract

The present invention relates to products and methods for the prevention and amelioration of bacterial contamination and degradation (spoiling) of biological material, particularly foodstuffs. In particular, the invention provides a product comprising an envelope of material defining a lumen wherein the lumen contains bacteriophage covalently attached to a surface.

Claims

1. An envelope of material defining a lumen wherein the lumen contains bacteriophage covalently attached to a surface.

2. An envelope of material defining a lumen according to claim 1, wherein the surface is the interior of the envelope.

3. An envelope of material defining a lumen according to claim 1, wherein the surface is within the lumen but separable or separated from the envelope.

4. An envelope of material defining a lumen according to claim 1, wherein the envelope is sealed.

5. (canceled)

6. (canceled)

7. An envelope of material defining a lumen according to claim 1, wherein the product is for containing biological material.

8. An envelope of material defining a lumen according to claim 7, wherein the biological material is plant material.

9. An envelope of material defining a lumen according to claim 1, wherein the product is for containing food.

10. An envelope of material defining a lumen according to claim 9, wherein the food is salad.

11. (canceled)

12. An envelope of material defining a lumen according to claim 9, wherein the food is meat.

13. (canceled)

14. An envelope of material defining a lumen according claim 8, wherein the plant material is not edible.

15. An envelope of material defining a lumen according to claim 7, wherein the plant material is one or more flowers.

16. An envelope of material defining a lumen according to claim 1, wherein the bacteriophage are active against bacteria selected from one or more of Campylobacter, Salmonella, Pseudomonas, Pectobacterium and Citrobacter.

17. An envelope of material defining a lumen according to claim 16, wherein the bacteriophage are active against bacteria of the genus Pseudomonas, preferably Pseudomonas aeruginosa.

18. An envelope of material defining a lumen according to claim 16, wherein the bacteriophage are active against bacteria of the genus Citrobacter.

19. A method of manufacturing the envelope of material defining a lumen of claim 1, comprising covalently attaching bacteriophage to the surface and forming the lumen from the material, enclosing the surface.

20. A method of packaging biological material, wherein the method comprises sealing biological material in the lumen of the envelope of material defining a lumen of claim 1.

21. Use of the envelope of material defining a lumen of claim 1 to control the number of bacteria on material sealed within the lumen of the envelope.

22. Use of the envelope of material defining a lumen according to claim 21 to preserve biological material.

23. Use of the envelope of material defining a lumen according to claim 22, wherein the preservation is temporary.

24. A system for packaging an object within the lumen of the envelope of material defining a lumen of claim 1 comprising: apparatus for covalently immobilising bacteriophage on the surface of the envelope; and apparatus for sealing the object in the lumen of the envelope.

Description

EXAMPLES AND DESCRIPTION OF THE DRAWINGS

[0063] The invention is now illustrated in the following specific embodiments with reference to the accompanying drawings showing:

[0064] FIG. 1 Results of Pectobacterium atrosepticum (Pba) 49075-induced spoilage on spinach leaves after 48 hours of incubation at 30 C. Image A shows a basil leaf treated with both bacteria and phage. Image B shows a basil leaf treated with just Pba 49075. Image C is a control (leaf left untreated).

[0065] FIG. 2 Spinach leaf utilised for Migration Study with Pba 49075 and bacteriophage 49075.

[0066] FIG. 3 Bar chart showing the extent of migration for both free and covalently immobilised phage.

[0067] FIG. 4 A reconstructed salad bag containing 50 g of spinach leaves.

[0068] FIG. 5 Screening of spinach leaves in the bag sections: Beginning (a), Middle (b) and End (c) following overnight enrichment of sampled bacteriophage. A control showing a Pba 49075 top agar lawn is shown in (d).

[0069] FIG. 6 Phage concentration per g of 49075 in the different salad bag sections

[0070] FIG. 7 Observational Evaluation of Shelf Life: (1=very fresh, 5=very decayed). Line indicates use by date; (A) appearance of freshness; (B) evenness of colour on each salad leaf; (C) gloss/even appearance of salad; (D) wilt and lack of rigour in salad leaves; (E) browning on the salad leaves (i) leaf edge browning and (ii) leaf surface browning.

[0071] FIG. 8 Number of Campylobacter jejuni isolated from chicken pieces following contamination and storage at three different conditions: a) stored for 72 h at 37 C.; b) stored for 120 h at 4 C.; c) stored for 16 h at room temperature.

[0072] FIG. 9 Number of Salmonella typhimurium isolated from chicken pieces following contamination and storage at three different conditions: a) stored for 72 h at 37 C.; b) stored for 120 h at 4 C.; c) stored for 16 h at room temperature.

[0073] FIG. 10 Number of Pseudomonas aeruginosa isolated from chicken pieces following contamination and storage at three different conditions: a) stored for 72 h at 37 C.; b) stored for 120 h at 4 C.; c) stored for 16 h at room temperature.

[0074] FIG. 11 Number of C. jejuni and S. typhimurium isolated from chicken pieces following contamination with a combination of these bacteria and storage at three different conditions: a) stored for 72 h at 37 C.; b) stored for 120 h at 4 C.; c) stored for 16 h at room temperature.

[0075] FIG. 12 Number of bacteriophages on chicken skin as a function of distance from the point of original inoculation.

[0076] FIG. 13 Photographs of the experiment described in Example 6A in which pieces of plastic sheets with the bacteriophage cocktail covalently immobilised thereon were placed on spinach leaves. Darker areas on leaves indicate a higher degree of rotting. Test samples are shown on the right and control samples on the left.

[0077] FIG. 14 Bar chart showing the quality of the control leaves vs the test leaves after 2 days at room temperature. The 4-point rating system described below in Table 5 was used to grade the leaves.

[0078] FIG. 15 Photographs of control and test leaves during the first day of the experiment described in Example 6. Test samples are shown on the right and control samples on the left.

[0079] FIG. 16 Results of the leaf spoilage experiment described in Example 6. The rating is an expression of edible leaves divided by total leaves. 0.5 was used as a cut-off point to compare respective shelf lives.

[0080] FIG. 17 Graph of the average freshness score of Baby Leaf Spinach exposed to a cocktail of bacteriophage covalently immobilised thereon as described in Example 7. Bags of Spinach were sampled every day to determine an average freshness score in a blinded trial. A freshness score of >3 was deemed acceptable. Spinach exposed to covalently immobilised bacteriophage had a substantially extended shelf-life.

[0081] FIG. 18 Graph showing the extension in shelf life of bagged spinach using a single bacteriophage (PMA) and two bacteriophage cocktails.

[0082] FIG. 19 Graph showing the extension in shelf life of bagged spinach using either bacteriophages covalently immobilised onto the packing (Immob. Phage) or sprayed onto the spinach (Adsorbed phage), controlled to salad alone.

EXAMPLE 1

Migration of Bacteriophage 49075 on Spinach Leaves

[0083] Observation of bacteriophage migration on spinach leaf surfaces demonstrated that bacteriophage originating from free and covalently immobilised bacteriophages can disperse themselves.

[0084] Bacteriophage 49075 and its corresponding host, Pectobacterium atrosepticum (Pba) 49075, a common plant pathogen, were used as a model to demonstrate phage migration. Immobilised bacteriophage were covalently attached to leaf surfaces treated with Pba 49075 alongside a free bacteriophage control. The extent to which the bacteriophages migrated across the leaves was measured.

[0085] To apply the bacteria, 1 mL of a 1/10 dilution of Pba 49075 overnight culture was dropped on a specific point on the leaf using a pipette. To apply the bacteriophage, 100 l of lysate were spotted on the same point the host was added.

[0086] The results of these experiments (shown in FIG. 1) demonstrate that Pba 49075 causes spoilage in basil leaves and that 49075 is effective at slowing this process.

[0087] In addition to the visual test presented in FIG. 1, cell counts were also carried out, where it was found that phage treatment resulted in a reduction in the bacterial count. In these experiments leaves were initially treated with 300 l of Pba 49075 (overnight culture) which was added to the leaf surface and evenly spread. 10 l of phage were then spotted on the leaf surface. The leaves were suspended in Petri dishes containing 2 mL of water to protect from desiccation. They were incubated at 30 C. overnight. Following this, the leaves were removed, weighed and submerged in 10 mL of PBS for 2 hours. The bacterial content of the PBS solutions was measured and the concentration per unit mass of the leaf section was calculated (results shown in Table 1).

TABLE-US-00001 TABLE 1 Mean bacterial concentration on leaves following treatment with 49075. Bacteriophage Bacteria Only Treatment Mean Bacterial Concentration (cfu/g) 7.1 10.sup.9 9.7 10.sup.8

[0088] This bacteriophage-host pair was used as a model to further investigate bacteriophage migration.

Migration Study

[0089] 49075 was demonstrated to migrate across spinach leaves containing Pba 49075 on their surfaces. The phage was at its highest quantity in the region to which it was applied, with a gradual decline in numbers moving away from this point (see FIGS. 2 & 3).

[0090] The leaves illustrated by FIG. 2 were kept suspended in Petri dishes with a small amount of water present at the base (to protect leaves against desiccation). 300 l of overnight Pba 49075 were added to the leaf surface and spread evenly. 10 l of 49075 lysate were spotted as shown above (in the case of covalently immobilised phage, 1 cm.sup.2 plastic sheet with covalently immobilised bacteriophage was placed on the leaf). Following 24 hours of incubation at 30 C., the leaves were cut into thirds as shown, with the bacteriophage content on each third being determined.

[0091] The Bacteriophage content for the leaf sections shown in FIG. 3 was determined by weighing a leaf section before leaving it to soak for 2 hours in 10 mL of PBS. Phage concentration for the PBS solution was measured using plaque assays and the original phage concentration per unit mass for the given leaf section was calculated.

[0092] We see from FIG. 3 that in the case of covalently immobilised bacteriophage, the decline in phage numbers across regions is not as sharp as that observed for free phage, where a reduction greater than 1 log was observed from the beginning region to the end region. As a control, leaves left untreated with bacteria were treated with phage in the same way as the test leaves; bacteriophage was only detected in the Beginning section, which was where it was applied.

EXAMPLE 2

[0093] Migration Study with Salad Bags

[0094] For this study, a migration study was carried out within salad bags to establish whether bacteriophages are also capable of dispersing across longer distances with more obstacles.

[0095] Salad bags measuring 24.510 cm (as illustrated in FIG. 4) were constructed from large Tesco 300 g spinach bags using a heat sealer. 50 g of spinach leaves were placed each bag. 10 mL of Pba 49075 were applied to the bag, which was sealed and inverted gently to distribute the bacteria inside it. An 84 cm sheet of plastic with covalently immobilised 49075 thereon was placed at the far end of the bag, which was sealed again. The bag was left to stand for 36 hours at room temperature, after which it was divided up into three equal thirds, labelled beginning, middle and end (Beginning referred to the section where the sheet of plastic bearing the covalently immobilised bacteriophage was present).

[0096] Initial testing was carried out to determine whether any bacteriophage migration occurred. Small cuts were made in the side of the bag for each section (beginning, middle and end). A swab was used to sample through the cut. Each swab was added to nutrient broth containing Pba 49075 in the log phase of growth and enriched overnight. The following day, each enriched sample was screened against the host.

[0097] To investigate the extent of migration, known quantities of leaves were removed from the bags and tested for phage content. This was done by suspending in 20 mL of PBS for 2 hours and determining the concentration of phage extracted from the leaves through plaque assays. Each bag section was sampled in triplicate.

[0098] Migration to the farthest bag section (end) was confirmed through the initial swab tests, with phage presence being used as an indicator (see FIG. 5).

[0099] The bacteriophage count results show that 49075 was at its highest level in the Beginning section. This section contained the sheet of plastic bearing the covalently immobilised bacteriophage. The concentration of 49075 dropped slightly (between 0.5-1 log) moving into the Middle section and remained at that level in the End section. The results are shown as a bar chart in FIG. 6 (see Bag 1 and Bag 2 in FIG. 6). Bags 1 and 2 were treated identically. Control 1 represents a salad bag treated with PBS only instead of Pba 49075 cells suspended in PBS. For Control 2, no liquid was added to the bag in addition to the covalently immobilised material in the Beginning section.

[0100] The concentrations in every bag section for the two controls were considerably lower than those of Bags 1 and 2 (see Controls 1 and 2 on FIG. 6). This was due to the absence of its corresponding Pba host, without which 49075 cannot grow. Despite Pba 49075 not being present, migration in Control 1 was still observed. In a similar pattern to Bags 1 and 2, phage content was highest in the Beginning section before dropping by almost 2 logs in the Middle and End sections. This migration can possibly be attributed to non-immobilised phage (adsorbed) getting knocked off/washing off the sheet and dispersing across the bag. No phage was detected in the Middle and End sections for Control 2. These results suggest that phage dispersion is greatly facilitated in the presence of a liquid medium, the absence of which results in undetectable levels of migration (Control 2). The presence of the corresponding host strain makes it possible for the phage to grow to a considerably higher level in all sections of the bag.

[0101] From these results we see that the presence of a fluid medium greatly increases the extent to which migration takes place. We note that moisture develops within salad bags as time passes by and this could help contribute to bacteriophage migration. The host strain was used in relatively large numbers and distributed across the whole salad bag for use in this experiment. In reality, much lower concentrations of undistributed bacteria will be encountered and this will affect bacteriophage migration.

EXAMPLE 3

The Shelf Life of Bagged Salad

[0102] The aim of this study was to demonstrate the antimicrobial performance of bacteriophages against Pectobacterium carotovorum in fresh cut salad leaves, and the effect that reducing the bacterial load had on product shelf life. P. carotovorum is a plant pathogen with a diverse host range and is widely associated with breakdown of foods within the supply chain.

Method

[0103] Six bags of 150 g of Florette Sweet Crispy salad were purchased, six days prior to their official use by date. The following groups were tested: [0104] 1. Control group. The leaves in the bag were sprayed with sterile water and heat sealed in the original bag. [0105] 2. Bacterial group. The leaves in the bag were inoculated with 200 cfu/g of P. carotovorum. [0106] 3. Bacteria+Phage covalently immobilised onto packaging. The leaves in the bag were inoculated with 200 cfu/g of P. carotovorum. In addition, bacteriophages were covalently immobilised onto the packaging, using the methods described in International patent applications WO 03/093462 and WO2007072049.

[0107] The packaging material was the original Florette salad bag and was subject to immobilisation using 1104 pfu/cm2 lysate. Each bag was heat sealed and tossed before storing at 4 C. throughout the experiment.

[0108] The salad leaves were evaluated daily for physical traits and every 2 days for microbiological analysis (where possible). 1 g samples were taken from the bags and bacteria were extracted. At all times, the visual assessment of the food product was based on a variety of key criteria specified by Kang, Kim and Choi (Kang, S. C., et al. (2007). Shelf-life extension of fresh-cut iceberg lettuce (Lactuca sativa L) by different antimicrobial films. J Microbiol Biotechnol vol. 17(8) pages 1284-1290). Scores for traits, ranging from 1 (very fresh) to 5 (very decayed), were recorded daily. The traits recorded were: browning, wilting, freshness, colour and gloss.

ResultsObservational Evaluation of Shelf Life

Overall Freshness

[0109] In accordance with Kang and Kim (2007) there was an observational analysis of key product traits for all trial groups. Overall freshness, which is a key parameter defined by Kang and Kim, indicates the general physical changes of the samples with time. It was observed that all samples did decay over the duration of the trial: however, the rate of decay and extent differed between samples.

[0110] Results for the appearance of freshness are shown in FIG. 7A (1=very fresh, 5=very decayed; line indicates use by date). FIG. 7A shows that the group that only had bacteria added to the salad leaves displayed a fast rate of decay and also the most extensive decay. This was followed by the untreated control group, indicating bacteria were already present on the salad to cause this decay. However, it is the group with the covalently immobilised bacteriophages on the packaging that demonstrated the least amount of decay, with no increase in observed decay after day 3 all the way through to day 8.

Colour Uniformity

[0111] Colour uniformity is used to indicate the visual appeal of the salad to the consumer, and this also demonstrated a variation due to the presence of P. carotovorum and bacteriophages. Results are shown in FIG. 7B: the bacteria-only group lost its colour uniformity at a faster rate than the other sample groups. The control bag, without any additions of bacteria, lost uniformity of colour at a slower rate. The group with covalently immobilised bacteriophages performed best with a significant difference to the other groups from day 4 to the end of the trial.

Gloss

[0112] Similar to colour uniformity, gloss gives an indication of the visual appeal of salad. Results are shown in FIG. 7C: both the control salad leaves and the deliberately contaminated salad leaves performed similarly, with decreasing gloss over the 8 day trial. The leaves in the group containing covalently immobilised bacteriophages, maintained a significantly higher gloss than the controls from day 1 onwards.

Wilting

[0113] After browning, wilting is a strong indicator of salad appeal. Results are shown in FIG. 7D: wilting was rapid in all samples groups. Again, the bacteria only group displayed the most extensive rate of wilting, whilst the covalently immobilised bacteriophage group showed a significant improvement beyond the use by date.

Browning

[0114] In relation to browning, two measures of were evaluated, they were: extent of browning around salad leaf edges and surface browning. Results are shown in FIGS. 7E(i) and (ii): The rate of browning was very high in the sample with added P. carotovorum bacteria. This was expected as browning is the most common effect of this bacteria. Again, at the shelf life point, the bag with covalently immobilised bacteriophages had the least amount of browning.

Conclusion Regarding Visual Results

[0115] The observations made on the visual aspects of the salad show that the bag with covalently immobilised bacteriophages on its surface performed consistently better than the other samples. However, even in the bag containing the covalently immobilised bacteriophage there is still some decay observed.

[0116] Thus these experiments demonstrate the effective reduction in bacterial load of P. carotovorum bacteria in bagged fresh cut salad by the presence of bacteriophages covalently immobilised onto the inside of the salad bag. Not only do bacteriophages directly reduce bacterial numbers but they also prevent visible signs of decay of the salad leaves by reducing browning and wilting. There was no further deterioration of all 5 key parameters of the salad from day 6 (the original shelf life) to day 8. This shows that the immobilisation of bacteriophages onto the surface of a salad bag can have a significant improvement on the deterioration on the contents of the bag.

EXAMPLE 4

Pathogenic Bacterial Reduction in Raw Chicken

[0117] This trial demonstrates the reduction in bacterial counts on raw chicken by using bacteriophages that are active against target bacteria strains. Both free bacteriophages and those covalently immobilised onto food packaging were used.

Experimental Design

[0118] Raw chicken was contaminated with the target bacteria and then wrapped in packaging. There were three experimental groups: [0119] 1. Control Group. Chicken contaminated with the target bacteria, and wrapped in standard food packaging. [0120] 2. Free Bacteriophage Group. Chicken contaminated with the target bacteria, with non-immobilised bacteriophage applied to the surface of the chicken and then wrapped in standard food packaging. [0121] 3. Covalently immobilised Bacteriophage Group. Chicken contaminated with the target bacteria, and wrapped in food packaging which has been coated with covalently immobilised bacteriophages that were attached using the Fixed Phage technology.

[0122] The above three groups were contaminated with; Campylobacter jejuni, Salmonella, and Pseudomonas aeruginosa and stored in the following storage conditions: [0123] a. stored for 72 hours at 37 C. [0124] b. stored for 120 hours at 4 C. [0125] c. stored for 16 hours at room temperature

[0126] At the end of the prescribed storage conditions each group was sampled to determine the number of bacteria present on the samples.

Methods

Media

[0127] All media used in this Example is detailed in table 2. All media was purchased premade or made according to the methods known in the art.

TABLE-US-00002 TABLE 2 Media used in Example 4. Medium Brain Heart Infusion Agar Brain Heart Infusion Broth Soft Brain Heart Infusion Agar X.L.D selective Salmonella agar Karmali selective Campylobacter agar PBS

Bacteria and Bacteriophages

[0128] Bacteria and bacteriophages were acquired from Fixed-Phage stores. All bacteria and bacteriophages used in this study are detailed in Table 2. All bacteria were cultured according to standard methods known in the art

TABLE-US-00003 TABLE 3 Bacteria and bacteriophages used in this study. Bacterium Selective Agar Lytic Bacteriophage C. jejuni Karmali CAMPY S. typhimurium X.L.D SHIELD P. aeruginosa Pseudomonas agar LIN24

Preparation and Inoculation of Chicken Broilers

[0129] Chicken broilers of thickness 50 mm were aseptically cut into 50 g slices using a sterile razor blade. Broilers were inoculated with a 2 mL solution containing a concentration of 110.sup.6 CFU/mL of appropriate bacteria in a PBS solution. The bacteria tested were C. jejuni alone, S. typhimurium alone, P. aeruginosa alone and a co-culture comprising C. jejuni and S. typhimurium. Slices used for negative controls were inoculated with 2 mL of sterile PBS. Each broiler was then incubated at RT for 30 min.

Preparation of Packaging Material

[0130] Polyamide/Polyethylene (PA/PE) composite vacuum wrap (Andrew James Worldwide) of thickness 0.2 mm was cut into 1528 cm bags. All bags to be treated with corona discharge were aseptically cut to allow treatment of the inner surface.

Immobilisation of Bacteriophages onto Packaging Material

[0131] Each packaging surface was treated with corona discharge. A bacteriophage solution of concentration of 110.sup.7 PFU/mL was prepared for immobilisation. Each packaging surface was treated by 2 corona discharge treatments at 7.5 kV as disclosed in WO 03/093462 and WO2007072049 and a 10 mL bacteriophage solution was aseptically applied to the surface. Each surface was then subjected to 3 washes with sterile PBS and dried under a laminar flow cabinet for 30 min. A small sample of the packaging material was retained for antimicrobial testing using the agar overlay method that is standard in the art.

Treatment of Chicken Surface with Bacteriophage

[0132] A sample of bacteriophage of concentration 0.510.sup.8 PFU/mL was prepared for the treatment of each chicken piece. Each chicken piece was inoculated with 2 mL of bacteriophage solution and incubated at room temperature for 30 min.

Storage of Chicken Samples

[0133] A single chicken piece was placed in each appropriate bag and each bag was vacuum sealed under aerobic conditions using a vacuum sealer (Andrew James). A total of 3 pieces were exposed to covalently immobilised bacteriophage and 3 pieces were exposed to non-immobilised bacteriophage. For controls, 1 non inoculated piece was exposed to covalently immobilised bacteriophage, 1 non inoculated piece was exposed to non-immobilised bacteriophage, 1 non inoculated piece was wrapped in food packaging with no treatment and 3 pieces inoculated with bacteria were wrapped in food packaging with no treatment. Chicken pieces were stored at 37 C. for 72 h for the accelerated tests, 4 C. for 120 h for the refrigerated tests and at room temperature for 16 h for the room temperature test.

Sampling of Chicken Broilers

[0134] Each chicken piece was aseptically cut into 3 separate 10 g pieces and each piece was added to 15 mL of sterile PBS. Each tube was then added to a rotary mixer at 400 RPM for 30 mins at room temperature. Each sample was then given 7 1/10 serial dilutions in sterile PBS and 310 l samples of each dilution were added to the appropriate selective agar. A 20 l sample was added to Karmali agar plates. The X.L.D and Pseudomonas agar plates were incubated for 72 h aerobically at 37 C. and Karmali agar plates were incubated for 72 h anaerobically at 37 C.

Sampling of Packaging Material

[0135] Samples of packaging material containing covalently immobilised bacteriophage, non-immobilised bacteriophage and untreated control were sampled for antimicrobial activity. A total of 3 samples were added to an agar overlay and incubated under aerobic conditions at 37 C. Antimicrobial activity was confirmed by the presence of zones of inhibition around the material.

Data Entry and Statistical Analysis

[0136] The data for bacteria isolated from each chicken broiler was plotted to determine frequency distribution and compared using a Kruskal-Wallis test with a 95% confidence interval. All statistical analysis was undertaken using GraphPad Prism 4 software.

Results

[0137] Isolation of Campylobacter jejuni from Treated Chicken Broilers

[0138] The number of Campylobacter jejuni isolated from chicken pieces following contamination and storage under the conditions above are shown in FIG. 8. No antimicrobial activity was noted on untreated material. No C. jejuni bacteria were isolated from the negative control chicken pieces from any tests.

[0139] In the accelerated test, significantly (p<0.001) less C. jejuni were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 610.sup.3 CFU, range 0-1.310.sup.5 CFU) and non-immobilised (median 1.210.sup.5 CFU, range 310.sup.3-5.110.sup.5 CFU) than the positive controls (median 3.310.sup.5 CFU, range 310.sup.4-3.310.sup.6 CFU) (FIG. 8a). Significantly (p<0.01) less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 8a).

[0140] For the room temperature test, significantly (P<0.01) less C. jejuni were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 510.sup.3 CFU, range 500-210.sup.4 CFU) than the positive controls (median 110.sup.4 CFU, range 500-1.110.sup.5 CFU). No significant difference was observed between the positive control and chicken pieces treated with non-immobilised bacteriophages (median 1.110.sup.4 CFU, range 510.sup.3-610.sup.4 CFU) (FIG. 8b). Significantly (p<0.01) less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 8b).

[0141] In the refrigerated test, significantly (p<0.001) less C. jejuni were recovered from chicken pieces treated with non-immobilised (median 1.410.sup.5 CFU, range 500-1.810.sup.6 CFU) and covalently immobilised bacteriophages (median 3.510.sup.5 CFU, range 510.sup.3-6.510.sup.4 CFU) than the positive controls (median 110.sup.6 CFU, range 1.1.sup.6-210.sup.6 CFU) (FIG. 8c). Significantly (p<0.001) less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 8c).

Isolation of Salmonella typhimurium from Treated Chicken Broilers.

[0142] The number of Salmonella typhimurium isolated from chicken pieces following contamination and storage under the conditions above are shown in FIG. 9. No antimicrobial activity was noted on untreated material. No S. typhimurium bacteria were isolated from the negative control pieces from any tests.

[0143] In the accelerated test, significantly (p<0.001) less S. typhimurium were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 310.sup.3 CFU, range 500-410.sup.4 CFU) than the positive controls (median 210.sup.7 CFU, range 110.sup.6-310.sup.8 CFU). No significant difference was observed between the positive control and chicken pieces treated with non-immobilised bacteriophages (median 110.sup.7 CFU, range 110.sup.6-310.sup.8 CFU) (FIG. 9a). Significantly (p<0.001) less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 9a).

[0144] For the room temperature test, significantly (p<0.001) less S. typhimurium were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 2.810.sup.3 CFU, range 400-2.810.sup.4 CFU) and non-immobilised bacteriophages (median 510.sup.3 CFU, range 110.sup.3-1.210.sup.5 CFU) than the positive controls (median 610.sup.4 CFU, range 110.sup.4-410.sup.5 CFU)(FIG. 9b). No significant difference was noted between bacteria isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 9b).

[0145] For the refrigerated test, significantly (p<0.001) less S. typhimurium were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 110.sup.3 CFU, range 0-2.310.sup.4 CFU) and non-immobilised bacteriophages (median 110.sup.4 CFU, range 200-810.sup.5 CFU) than the positive controls (median 2.210.sup.5 CFU, range 500-910.sup.5 CFU) (FIG. 9c). Significantly (p<0.05) less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage.

Isolation of Pseudomonas aeruginosa from Treated Chicken Broilers.

[0146] The number of Pseudomonas aeruginosa isolated from chicken pieces following contamination and storage under the conditions above are shown in FIG. 10. No antimicrobial activity was noted on untreated material. No P. aeruginosa bacteria were isolated from the negative control pieces from any tests.

[0147] In the accelerated test, significantly (p<0.001) less P. aeruginosa were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 210.sup.3 CFU, range 500-510.sup.3 CFU) and significantly (p<0.01) less P. aeruginosa non-immobilised bacteriophage (median 1.510.sup.4 CFU, range 510.sup.3-210.sup.5 CFU) than the positive controls (median 110.sup.5 CFU, range 510.sup.4-310.sup.5 CFU) (FIG. 10a). Significantly less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 10a).

[0148] For the room temperature test, significantly (p<0.001) less P. aeruginosa were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 1050 CFU, range 500-410.sup.3 CFU) and non-immobilised bacteriophages (median 110.sup.3 CFU, range 500-110.sup.4 CFU) than the positive controls (median 5.510.sup.3 CFU, range 510.sup.3-310.sup.4 CFU)(FIG. 10b). No significant difference was noted between bacteria isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 10b).

[0149] For the refrigerated test, significantly (p<0.001) less P. aeruginosa were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 110.sup.3 CFU, range 500-210.sup.3 CFU) and non-immobilised bacteriophages (median 510.sup.3 CFU, range 500-110.sup.4 CFU) than the positive controls (median 510.sup.3 CFU, range 510.sup.3-2.510.sup.4 CFU) (FIG. 10c). Significantly (p<0.05) less bacteria were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage.

Isolation of Co-Cultured C. jejuni and S. typhimurium Bacteria from Treated Chicken Broilers

[0150] The test for single bacteria types was repeated with a combination of bacteria: namely C. jejuni and S. typhimurium. The number of each type of bacteria isolated from chicken pieces following contamination and storage under the conditions above are shown in FIG. 11.

[0151] No C. jejuni or S. typhimurium bacteria were isolated from the negative control pieces from any tests. In the accelerated test, significantly less C. jejuni were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 2.510.sup.3 CFU, range 500-110.sup.4 CFU) and non-immobilised bacteriophage (median 510.sup.4 CFU, range 510.sup.3-1.510.sup.5 CFU) than the positive controls (median 110.sup.6 CFU, range 510.sup.5-310.sup.6 CFU) (FIG. 11a). Significantly (p<0.001) less S. typhimurium were also recovered from chicken pieces treated with covalently immobilised bacteriophage (median 110.sup.4 CFU, range 110.sup.3-810.sup.4 CFU) and with non-immobilised bacteriophage (median 2.210.sup.5, range 1.910.sup.3-510.sup.6 CFU) than the positive control (median 310.sup.6, range 110.sup.6-810.sup.6 CFU) (FIG. 11a). Significantly (p<0.01) less C. jejuni and S. typhimurium were isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage.

[0152] For the room temperature test, significantly less C. jejuni were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 300 CFU, range 50-410.sup.3 CFU) and non-immobilised bacteriophage (median 510.sup.3 CFU, range 500-210.sup.4 CFU) than the positive controls (median 1.510.sup.4 CFU, range 1.510.sup.3-610.sup.4 CFU) (FIG. 11a). Significantly less S. typhimurium were also recovered from chicken pieces treated with covalently immobilised bacteriophage (median 800 CFU, range 100-210.sup.4 CFU) and with non-immobilised bacteriophage (median 110.sup.3, range 100-110.sup.4 CFU) than the positive control (median 110.sup.4, range 110.sup.3-810.sup.4 CFU) (FIG. 11a). No significant difference was observed between C. jejuni isolated from both chicken treatments and significantly (p<0.05) less S. typhimurium was isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 11a).

[0153] For the refrigerated test, significantly less C. jejuni were recovered from chicken pieces treated with covalently immobilised bacteriophages (median 110.sup.3 CFU, range 450-4.510.sup.3 CFU) and non-immobilised bacteriophage (median 2.510.sup.3 CFU, range 110.sup.3-2.510.sup.4 CFU) than the positive controls (median 1.510.sup.4 CFU, range 510.sup.3-510.sup.4 CFU) (FIG. 11a). Significantly less S. typhimurium were also recovered from chicken pieces treated with covalently immobilised bacteriophage (median 310.sup.3 CFU, range 210.sup.3-810.sup.3 CFU) and with non-immobilised bacteriophage (median 110.sup.4, range 110.sup.3-510.sup.4 CFU) than the positive control (median 610.sup.4, range 110.sup.4-1.610.sup.5 CFU) (FIG. 11c). No significant difference was observed between C. jejuni isolated from both chicken treatments and significantly (p<0.05) less S. typhimurium was isolated from chicken pieces treated with covalently immobilised bacteriophage than chicken pieces treated with non-immobilised bacteriophage (FIG. 11c).

Conclusions

[0154] Thus, it is demonstrated that bacteriophages covalently immobilised on food packaging can significantly reduce pathogenic strains of bacteria from raw chicken pieces. In some cases, there was a 5 log reduction in bacterial count. Free bacteriophages showed a lower reduction in bacterial counts than bacteriophages covalently immobilised onto packaging.

EXAMPLE 5

Migration of Bacteriophage Across Chicken

[0155] A key factor in determining the effectiveness of immobilisation of bacteriophage onto food packaging is in treating food that is remote from the packaging surface. To investigate this, experiments were carried out to determine the extent of migration of bacteriophage across chicken skin from an initial point.

Experimental Methods

[0156] The experimental model used chicken skin. For this model, there were two experimental groups used: [0157] 1. Chicken skin to which only bacteriophages were added. [0158] 2. Chicken skin to which both bacteria (Campylobacter jejuni) and bacteriophages were added.

[0159] In the group containing bacteria, a 30 l sample of C. jejuni (110.sup.7 cfu/mL) was evenly spread over the chicken skin 65 cm.sup.2. This resulted in an even distribution of 3105 cfu/cm.sup.2 of skin. In both groups, 10 l of bacteriophage lysate (110.sup.8 pfu/mL) was added at a point on the chicken skins. The skins were then covered with a polyethylene film and incubated at 4 C. Samples were taken from the chicken skin after 16 hours at various points along the chicken skin which were; 0.5, 1, 1.5 and 2 cm from the point of the original bacteriophage inoculation. These samples were assayed for bacteriophages.

Results

[0160] In both groups, i.e. with bacteria and without, bacteriophages were isolated from the chicken skin. In the group that did not have any bacteria, some bacteriophages were isolated from the skin up to a distance of 1 cm from the point of original inoculation.

[0161] In the group for which C. jejuni bacteria was added there was a high rate of migration, with significant levels of bacteriophage found at distances greater than 2 cm from the point of original inoculation. These results are presented in FIG. 12. (This graph has a logarithmic scale and therefore, 1 pfu=0 pfu).

Conclusions

[0162] This study illustrates the extent that bacteriophages can migrate over raw chicken skin from a fixed point. It also shows that the distance they are able to migrate can be several centimetres in just a few hours. This migration may stem from a number of reasons. First, as each bacterial cell is infected it may migrate some distance before bursting and releasing new bacteriophages to go on and infect further bacterial hosts. Secondly, each bacteriophage may be capable of clearing (and therefore moving through) an area with a radius of 0.1 cm of bacteria. Both of these factors allows bacteriophages to spread relatively long distances over chicken skin from an initial point.

Experimental Methods

Preparation of Growth Media

[0163] All laboratory microbiological and bacteriophage media used herein were acquired from Oxoid. Phosphate buffered saline (PBS) was acquired from Fisher Scientific and used as a diluent. All microbiological media were prepared according to manufacturer's instructions using distilled water. Prepared media was sterilised using steam sterilisation at 121 C. for 15 minutes, before use. If not used immediately, microbiological media was stored at room temperature for a maximum of 2 weeks. Before use, solid agar was melted by microwave for 5 minutes at 800 W. Agar plates were aseptically poured in a microbiological fume hood to maintain sterility, with 20 mL of molten agar per plate and air dried for 30 minutes. Liquid media was prepared by using aseptic technique to aliquot into sterile tubes.

Validation of Test Bacteria and Bacteriophages

[0164] Growth of the bacteria on the appropriate microbiological media indicated viable stocks. Solutions of bacteriophages with a titre of 110.sup.8 plaque forming units (PFU)/mL, were used as a starter titre. To determine the concentration of bacteriophage in solution, the solution was subjected to 8 1/10 serial dilutions in sterile PBS. A sample of each dilution was tested using the agar overlay method. A clear plaque in the growth media indicated viable bacteriophage and the bacteriophage concentration was determined by counting the number of plaques in the lowest dilution.

[0165] The invention thus provides packaging materials for preservation of objects including foodstuffs, uses for the packaging material and methods and systems for production of these packaging materials.

EXAMPLE 6

Studies on Spinach Leaves

[0166] A model system was developed using leaves sandwiched between two sheets of plastic. These sheets of plastic can be coated with covalently immobilised bacteriophage allowing parameters relating to food packaging to be tested.

Experiment A

[0167] This experiment was carried out using a two-bacteriophage cocktail targeting L. amingen, a bacterial strain which had previously been determined to cause spoilage in spinach leaves. The cocktail was covalently immobilised onto plastic sheets (1 side). Following this, the sheets of plastic bearing the covalently immobilised bacteriophage were cut into smaller pieces. Five spinach leaves from Morrison's (a UK supermarket chain) were put in a square culture dish. A single piece of plastic sheet bearing the covalently immobilised bacteriophage was placed (bacteriophage side facing down) on each leaf. A control of five untreated leaves was also set up in a separate square culture dish. After being left to stand for 2 days at room temperature, the leaves were observed and rated using the 4-point rating system described in Table 5. The results of these experiments are shown in FIGS. 13 and 14.

[0168] Leaves in contact with plastic sheet bearing the covalently immobilised bacteriophage appeared to be in a better condition than the untreated control group. Thus the covalently immobilised phage cocktail is effective at protecting the leaves from spoilage bacteria present on the surface.

Experiment B

[0169] In contrast to experiment A, for this experiment, a different cocktail of 16 bacteriophages (isolated for this project) was used. Instead of small plastic sheet clippings, entire sheets were used to sandwich the leaves, simulating a bag environment. The bacteriophage cocktail was covalently immobilised onto plastic sheets, and an experiment was set up in square culture dishes, with nine leaves used per sheet. The control experiment was sandwiching the leaves in between two plain plastic sheets without any covalently immobilised bacteriophage.

[0170] Instead of the 4-point grading system (c.f. Table 5), leaves were graded using an edibility scale, which involved grading the leaves as either edible or inedible every day the experiment was running. The overall edibility score was determined by dividing the number of edible leaves by the total (9). The results of these experiments are shown in FIG. 16.

EXAMPLE 7

Salad Bag Spoilage Studies

Setup

[0171] Baby leaf Spinach was acquired from Morrison's supermarket on the day of the trial with each bag containing 160 grams and measuring 21 cm by 21 cm. Bags were inspected to ensure no spoilage had occurred and that it had 3 days of advertised shelf life. A total of 3 bags were used for each of the following trial conditions.

Bacteriophage Cocktail

[0172] The prototype bacteriophage cocktail used in initial studies was composed of 3 bacteriophages (Table 4). Each individual bacteriophage solution was purified using dialysis before the study. A 10 mL solution of each bacteriophage was added to a dialysis membrane and incubated at 4 C. for 24 h in PBS.

TABLE-US-00004 TABLE 4 Constituents of the bacteriophage cocktail used in this study Initial Concentration before Bacteriophage Target Host Dialysis (PFU/mL) Fluorescens Pseudomonas fluorescens 3 10.sup.9 PFS Pseudomonas fluorescens 2 10.sup.9 LAX Leloitta amnigen 1.1 10.sup.10

Application of Treatments

[0173] For covalently immobilised bacteriophage and water, polypropylene film measuring 20 cm20 cm was subjected to 2 corona discharge treatments at 7.5 kV and 2 mL of bacteriophage solution was applied to the surface. All sheets were dried in a laminar flow cabinet for 30 mins and two sheets were added to the appropriate spinach bag on the top and the bottom to cover all the leaves. For the water control, sterile distilled water was sprayed onto PA/PE films and subjected to 2corona discharge treatments at 7.5 kV. For adsorbed bacteriophage treatment, 2 mL of bacteriophage solution was sprayed onto the leaves and the bag shook to distribute the bacteriophage solution.

Incubation and Sampling of Salads

[0174] Each study was randomised and blinded and each salad bag was incubated for 144 h and sampling occurred every 24 h.

Spoilage Analysis of Salads

[0175] The spoilage of each salad bag was assessed by 3 trained members of staff. Spoilage was assessed using the method previously described in Garcia-Gimeno and G. Zurera-Cosano and summarised in Table 5 (Determination of ready-to-eat vegetable salad shelf-life (1997). Int. J. Food Microbiol. 36: 31-38). Browning, colour and texture were assessed to create an average freshness score of each bag.

TABLE-US-00005 TABLE 5 Freshness Rating Description 4 - Very Good All leaves or single leaf in close to perfect condition Consistent colour across the whole leaf No wilting or breakdown at edges of leaf No visible browning on any part of leaf 3- Good Most leaves or single leaf in good condition Minor colour changes such as leaf darkening or very small wet patches may be present - (in some leaves) Leaves may be curled or wilted at the edges Evidence of minor browning at leaf edges 2- Fair Most leaves or single leaf in passable condition - edible but of general poor appearance. Colour changes such as leaf darkening may be present - (in some leaves) Visible wilting or structural breakdown i.e. holes Browning visible on ~30% of leaf (on average) 1 - Poor Most leaves or single leaf in poor condition - small sections with a good appearance may remain. Major colour changes such as leaf darkening may be present - (in some leaves) Leaves show evidence of structural breakdown Browning visible on >50% of leaf 0 - Unacceptable Most leaves or single leaf in totally inedible condition. Total breakdown of all leaf structure. Leaves are completely brown (>80% of leaves).

ResultsSpoilage Studies

[0176] Each bag of spinach was assessed daily for freshness scores. A freshness score of 3+ was determined to be acceptable.

[0177] All spinach samples were found to decrease in freshness score over time (FIG. 17). Results show that bacteriophages covalently immobilised onto packaging materials can extend the shelf-life of bagged salad for >1 day at a cut-off of 3 and >2 days at a cut-off of two. This result has been replicated with salad produced in Spain (see FIG. 6 for an example) and Italy (results not shown), demonstrating that the bacteriophage cocktail is suitable for use throughout Europe (and possibly beyond) and that it can effectively reduce spoilage in salads. It would be expected that if the covalently immobilised bacteriophages were introduced at an earlier point in the production process (i.e. when the salad is first bagged) would result in even an even greater extension of shelf-life.

[0178] Similar results have been obtained using both single phage and a variation of the cocktail described above (FIG. 18). PMA (a single phage), replaced one of the bacteriophages in the original cocktail (Cocktail 1) to give an improved cocktail (Cocktail 2) which had similar efficacy but which gave higher yields in liquid culture, indicating it would be easier to industrialise and produce in large quantities.

[0179] The ability of covalently immobilised bacteriophage to extend shelf-life was also compared to non-immobilised bacteriophages. While a real advantage of the covalently immobilised bacteriophages is the ability to deploy them in a standard plastic sheet which is compatible with existing manufacturing processes, rather than as a liquid that needs to be stored at 4 C., covalently immobilised/attached bacteriophages were surprisingly also shown to be more effective at extending shelf-life than free bacteriophages (FIG. 17). Covalently immobilised bacteriophages extended the shelf-life of the salad consistent with previous experiments, but the same cocktail when not covalently immobilised (adsorbed bacteriophages), while yielding some shelf life extension, was clearly inferior to the covalently immobilised bacteriophages.

[0180] Hence the invention provides anti-bacterial packaging, manufacture and use thereof.