MICROBIOLOGICAL CULTURE DEVICE COMPRISING A SHEET OF DEHYDRATED POLYSACCHARIDE HYDROGEL

Abstract

A microbiological culture device including: a part made of absorbent material having an at least substantially planar upper face and incorporating into its thickness a dehydrated culture medium composition, resting on the part made of absorbent material, a sheet of dehydrated polysaccharide hydrogel which can be rehydrated at temperatures of between 5 C. and 40 C.; said sheet of dehydrated hydrogel being affixed directly on the upper face of the part made of absorbent material, or indirectly, through a permeable membrane insert.

Claims

1. A microbiological culture device, comprising: a part made of absorbent material having an at least substantially planar upper face and incorporating into its thickness a dehydrated culture medium composition, resting on said part made of absorbent material, a sheet of dehydrated polysaccharide hydrogel which can be rehydrated at temperatures of between 5 C. and 40 C.; said sheet of dehydrated hydrogel being affixed directly on the upper face of said part made of absorbent material, or indirectly, through a permeable membrane insert.

2. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel is a sheet of dehydrated hydrogel of gellan, xanthan, galactomannan or starch and/or of a mixture thereof.

3. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel was prepared by dehydration of a layer of hydrogel of water-based composition and of at least one polysaccharide gelling agent chosen from a gellan gum, a xanthan gum, a galactomannan gum, starch and a mixture thereof.

4. The microbiological culture device as claimed in claim 3, wherein said sheet of dehydrated polysaccharide hydrogel is obtained by dehydration of a layer of polysaccharide hydrogel prepared by mixing 0.1 to 30 g of at least one polysaccharide gelling agent into a liter of water.

5. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel is obtained by dehydration of a layer of gellan hydrogel, prepared beforehand by mixing 10 to 20 g of gellan gum.

6. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel is obtained by dehydration of a layer of xanthan hydrogel, prepared beforehand by mixing 0.2 to 10 g of xanthan gum into a liter of water.

7. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel is obtained by dehydration of a layer of xanthan and galactomannan hydrogel, prepared beforehand from a mixture of xanthan gum and locust bean gum.

8. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel is obtained by dehydration of a layer of starch hydrogel, prepared beforehand by mixing 0.5 to 15 g of starch into a liter of water.

9. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel is obtained by dehydration of a layer of gellan and starch hydrogel, prepared from a mixture of gellan gum and starch, with a [gellan gum]/[starch] weight ratio of between 40:1 and 2:3.

10. The microbiological culture device as claimed in claim 4, wherein said sheet of dehydrated polysaccharide hydrogel is structurally reinforced chemically by means of a reinforcing additive chosen from glycerol, ethylene glycol and polyethylene glycol.

11. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel further comprises at least one curing agent chosen from divalent cation salts.

12. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel further comprises at least one curing agent chosen from magnesium chloride (MgCl.sub.2), calcium chloride (CaCl.sub.2), magnesium sulfate (MgSO.sub.4) and manganese chloride (MnCl.sub.2).

13. The microbiological culture device as claimed in claim 1, wherein said sheet of dehydrated polysaccharide hydrogel further comprises at least one plasticizer.

14. The microbiological culture device as claimed in claim 1, wherein non-calendered, said part made of absorbent material has a surface density of between 50 g.m.sup.2 and 150 g.m.sup.2, for a thickness of between 0.5 mm and 10 mm.

15. A microbiological culture device in a kit to be assembled, comprising: at least one part made of absorbent material having an at least substantially planar upper face and incorporating into its thickness a dehydrated culture medium composition, at least one sheet of dehydrated polysaccharide hydrogel which can be rehydrated at temperatures of between 5 C. and 40 C., and optionally at least one permeable membrane insert.

16. The microbiological culture device in a kit to be assembled, comprising: at least one part made of absorbent material having an at least substantially planar upper face and incorporating into its thickness a dehydrated culture medium composition, at least one sheet of dehydrated polysaccharide hydrogel which can be rehydrated at temperatures of between 5 C. and 40 C., and optionally at least one permeable membrane insert enabling the assembly of a microbiological culture device as defined by claim 1.

Description

EXAMPLES

[0126] A/Microbiological Culture Device According to the Invention, and General Principle of Use

[0127] As shown in FIG. 1, a microbiological culture device according to the invention is firstly composed of a part made of absorbent material 1 which is more or less thick and of a sheet of dehydrated polysaccharide hydrogel 2, of lesser thickness. In the example depicted, these two elements 1 and 2 are of substantially square shape.

[0128] The part made of absorbent material 1, made from hydrophilic and non-water-soluble material, incorporates a dehydrated culture medium composition in its thickness. The sheet of dehydrated polysaccharide hydrogel 2 is formed by drying/dehydration of a layer of polysaccharide hydrogel, and its mechanical structure can be reinforced using a fibrous reinforcement, for example a woven.

[0129] The part made of absorbent material 1 and the sheet of dehydrated polysaccharide hydrogel 2 may be provided already preassembled, secured together, or else in the form of two mechanically independent elements.

[0130] The design and the manufacture of this part made of absorbent material 1 and of this sheet of dehydrated polysaccharide hydrogel 2 will be described in greater detail in the remainder of the examples.

[0131] As secondary characteristic, a receptacle 4 is associated with the microbiological culture device in order to facilitate the handling thereof, especially for the step of rehydration and activation of the device, and for any movement (for example transfer from the lab table to the incubator).

[0132] The use of a microbiological culture device according to the invention requires activation of the device by virtue of hydration, by the part made of absorbent material 1, by water 4.

[0133] For this purpose, the microbiological culture device according to the invention is placed inside the receptacle 4, with the sheet of dehydrated polysaccharide hydrogel 2 turned upwards. Since the receptacle 4 has a larger surface area than that of the culture device, the water 5 is poured into the receptacle 4, taking care not to pour it directly on the sheet of dehydrated polysaccharide hydrogel 2. The volume of water used is more or less calibrated to be able to sufficiently moisten the part made of absorbent material 1 and dissolve the culture medium composition which it contains.

[0134] Another way of proceeding consists in pouring the suitable volume of water into the bottom of the receptacle 4, then in depositing the part made of absorbent material 1 surmounted by the sheet of dehydrated polysaccharide hydrogel 2 therein. Care will be taken not to place the sheet of dehydrated polysaccharide hydrogel 2 directly in contact with the free water, such that the device is indeed only hydrated by the part made of absorbent material 1.

[0135] When the microbiological culture device according to the invention is provided with the part made of absorbent material 1 and the sheet of dehydrated polysaccharide hydrogel 2 in the form of two mechanically independent elements, the step of hydration can then be carried out in a third way. The part made of absorbent material 1 is then placed inside the receptacle 4. In the receptacle 4 and optionally directly on this part made of absorbent material 1, a sufficient amount of water 5 is poured to thoroughly soak the part made of absorbent material 1. The surface thereof is subsequently covered with the sheet of dehydrated polysaccharide hydrogel 2.

[0136] During the activation of a microbiological culture device according to the invention, the hydration by the part made of absorbent material 1 makes it possible firstly to dissolve the culture medium composition contained in the thickness of the part made of absorbent material 1. Secondly, this activation is continued by the hydration of the sheet of dehydrated polysaccharide hydrogel 2, applied to the surface of the part made of absorbent material 1. This rehydration of the sheet of dehydrated polysaccharide hydrogel 2 causes a layer of rehydrated polysaccharide hydrogel 2 to appear at the surface of the part made of absorbent material 1 that is swollen, not by just the water originating from the part made of absorbent material 1 but rather by a culture medium solution originating from the part made of absorbent material 1.

[0137] Thus activated, the cell culture device is ready to receive the sample to be analyzed. Once the sample has been inoculated on the device, especially by operations of streaking and spreading the cells, for example by means of a loop 6, the assembly is incubated at an established temperature and for an established duration, before reading the results.

[0138] Due to its quite particular consistency and texture, the layer/film of rehydrated polysaccharide hydrogel 2 of a microbiological culture device according to the invention makes it possible to create a culture surface that is both lubricated and adherent for the cells, able to receive microorganisms and enable the isolation thereof by mechanical means and operations conventionally used to streak the cells over the surface of a conventional agar-based medium. Moreover, due to its large exposure to gas exchanges and to phenomena of drying out and due to its hyper-absorbent properties, this layer/film of polysaccharide hydrogel 2 will be able to self-regenerate continuously throughout the incubation period with the culture medium solution originating from the part made of absorbent material 1.

[0139] As also depicted in FIG. 1, the microbiological culture device may also incorporate a permeable membrane insert 3 that is inserted between the part made of absorbent material 1 and the sheet of dehydrated polysaccharide hydrogel 2. Produced in a permeable material, this optional permeable membrane insert 3 may be used for highly varied purposes, for instance: [0140] to provide additional stiffness and/or mechanical strength to the whole system, or only to the sheet of dehydrated polysaccharide hydrogel 2 and to the layer of rehydrated polysaccharide hydrogel 2, [0141] to improve the contact of the part made of absorbent material 1 with the sheet of dehydrated polysaccharide hydrogel 2 and/or with the layer of rehydrated polysaccharide hydrogel 2, [0142] to serve as a reservoir layer for retaining particular compounds, which are intended to be mixed with the dissolved culture medium composition originating from the part made of absorbent material 1 before reaching the layer of rehydrated polysaccharide hydrogel 2, [0143] to improve the contrast and observation of the colonies growing on the surface of the microbiological culture device.

[0144] B/Manufacture of the Different Constituent Elements of a Microbiological Culture Device According to the Invention [0145] B1/The part made of absorbent material incorporating, into its thickness, a dehydrated culture medium composition

[0146] Regarding the part made of absorbent material 1 which forms part of a microbiological culture device according to the invention, said part is made from a three-dimensional support with an open, porous structure able to receive within it equally well a liquid (in particular an aqueous liquid) and solid particles with a suitable particle size.

[0147] For the examples and tests which follow, the microbiological culture devices tested comprise a part made of absorbent material incorporating a dry or dehydrated culture medium composition, produced from the nonwoven Airlaid SCA95NN81, from SCA (Sweden). This two-component PET/CoPET (Polyester/coPolyester) nonwoven was specially treated to be able to be made adhesive simply by hot pressing (calendering) without adding adhesive. It is also characterized by a surface density before calendering (or non-calendered) of the order of 95 g.m.sup.2 for a thickness of 2 mm. Parts with sides of approximately 6 cm were cut from this nonwoven.

[0148] The incorporation of a dehydrated culture medium composition within the very bulk of these parts made of fibrous material was carried out with a dry impregnation technique. To this end, approximately 0.2 g of a culture medium composition formulated in powder form are sprinkled over each cut nonwoven part. The assembly is placed between two electrodes applying a voltage of 3200 V.mm.sup.1, for 15 seconds with relative humidity of between 35% and 45%.

[0149] Once the dry impregnation is completed, the nonwoven parts are calendered at 60 C. by applying a pressure of 3.10.sup.5 Pa.Math.cm.sup.2. [0150] B2/The culture media formulated as powder

[0151] With a view to testing the microbiological culture devices according to the invention, different dehydrated culture medium compositions were used. These have the composition of the agar-based culture media distributed by bioMrieux (France), with the exception of agar agar and other texturizing agents. These were more particularly the media of the range chromID (for example chromID CPS Elite, chromID S. aureus, chromID P. aeruginosa, chromID VRE, chromID Salmonella Elite).

[0152] The microbiological culture devices according to the invention, produced in this way, were then able to be tested for the detection and isolation of bacteria such as Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter cloacae, Clostridium freundii, Streptococcus agalactiae and Serratia marcescens.

[0153] A selection of the results obtained is presented in FIGS. 3 to 13, in the form of photographs. [0154] B3/The sheets of dehydrated polysaccharide hydrogel

[0155] The sheets of dehydrated polysaccharide hydrogel 2 which form part of the microbiological culture devices according to the invention are primarily designed such that, once they are rehydrated, they can offer the microorganisms a support suited to their growth and development. The composition and the consistency of these sheets of dehydrated polysaccharide hydrogel 2 were also specifically studied to obtain surfaces suitable for operations of isolation and streaking of cells, whether these sheets of polysaccharide hydrogel are in a rehydrated or dehydrated state.

[0156] For the following examples and tests, the sheets of dehydrated polysaccharide hydrogel 2 forming microbiological culture devices according to the invention were prepared following the general method below. [0157] a) Preparation of the polysaccharide hydrogels: [0158] Heat 500 ml of sterile distilled water in a glass flask on a hot plate. [0159] Add the gelling agent(s) in a defined amount and wait for the mixture to be homogeneous and translucent, continuing to heat (bring to boiling or close to boiling). [0160] After complete dissolution, add the glycerol, homogenize and add the divalent cation salt(s) serving as binder and curing agent, homogenize and bring to boiling. [0161] Spread 5 to 15 ml (depending on the thickness desired for the sheet) of the still hot mixture into Petri dishes 47 mm in diameter. [0162] Leave to cool and harden on the lab table, until the gelling agent has set. [0163] Remove the hydrogel parts from their mold, using a scalpel if necessary. [0164] b) Dehydration of the polysaccharide hydrogels: [0165] Clamp the hydrogel parts between 2 sheets of absorbent paper. [0166] Place the assembly in the oven, at a temperature of the order of 40 C., for 1 to 6 hours; the operation may also be carried out for at least one night, in a dry heat oven brought to 32 C.

[0167] FIG. 2 is a photograph showing the sheets of dehydrated hydrogel on leaving the oven. By way of indication, with 7 ml of hydrogel preparation poured into the Petri dishes, the thickness of the hydrogel parts is of the order of 3 mm, before their preparation passage in the oven. After dehydration, the sheets are less than 1 mm thick.

[0168] The sheets of dehydrated polysaccharide hydrogel 2 of a microbiological culture device according to the invention were modified into different versions, by varying, especially: [0169] the nature of the polysaccharide gelling agent (for example gellan gum, xanthan gum, galactomannan gum, starch, sodium alginate, pectin, methyl cellulose and hydroxymethyl cellulose), [0170] the proportion between the water and the gelling agent, used during the step of preparing the polysaccharide hydrogels, [0171] the nature and the amount of any curing agents used in the preparation of the polysaccharide hydrogels, [0172] the nature and the amount of any additives used to improve the physicochemical properties of the (hydrated) polysaccharide hydrogels and/or of the sheets of dehydrated polysaccharide hydrogel.

[0173] B4/The permeable membrane insert (optional)

[0174] With a view to improving contrast and the observation of the colonies growing on the surface of the microbiological culture device, a membrane that is opaque to light and with a high level of whiteness (for example a CIE whiteness at least equal to 65) may be inserted between the part made of absorbent material and the sheet of dehydrated polysaccharide hydrogel. This permeable membrane insert may consist of a sheet of absorbent paper, of cellulosic composition.

[0175] C/Evaluation of the microbiological culture devices according to the invention

[0176] For the sheets of dehydrated polysaccharide hydrogel which have a solid surface, a structural integrity and satisfactory mechanical strength, tests were carried out with a view to evaluating their ability to form microbiological culture supports which both have good performance and are compatible with the operations and mechanical means for streaking and spreading cells.

[0177] In this context, bacterial cultures were produced especially with strains of Escherichia coli, of Enterococcus faecalis, of Proteus mirabilis of Staphylococcus aureus, of Serratia marcescens, of Pseudomonas aeruginosa, of Enterobacter cloacae, Clostridium freundii and of Cronobacter sakazaki. Depending on the bacteria of interest to be cultured, the sheets of dehydrated polysaccharide hydrogel to be tested are combined with parts made of absorbent material incorporating, in their thickness, a particular dehydrated culture medium composition. The particular feature of this dehydrated culture medium composition lies in the fact that it has been chosen to be suitable for the growth and development of the bacteria of interest, and that it incorporates chromogenic components facilitating the visual identification of these bacteria of interest.

[0178] For this purpose, the parts made of absorbent material which incorporate, in their thickness, a dehydrated culture medium composition, are placed in Petri dishes 90 mm in diameter, then moistened with 6 to 7 ml of sterile distilled water. These parts made of absorbent material are then surmounted by a sheet of dehydrated polysaccharide hydrogel. Once the hydration of the part made of absorbent material has been carried out, the culture medium has been activated and the layer of polysaccharide hydrogel has been regenerated, the microbiological culture device is inoculated by 10 l of a calibrated solution containing a theoretical bacterial load of 10.sup.7 CFU/ml. The cell sample is deposited by means of a first loop on the first quadrant of the hydrogel surface. The second quadrant is inoculated with a new loop, by drawing out several streaks from the first quadrant. The third quadrant is inoculated like the second without changing the loop. The fourth quadrant is inoculated with streaks not drawn out from the second quadrant.

[0179] The dishes are placed in a jar with a small amount of water such that the microbiological culture devices do not dry out. The assembly is then incubated at 37 C. for 24 hours.

[0180] Some of the results obtained were compiled and presented in FIGS. 3 to 13 in the form of photographs.

[0181] FIG. 3 shows photographs of cultures and isolations of E. coli conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 13 g/1 gellan hydrogels (that is to say 13 g of gellan gum per 1 liter of water), with a structure reinforced with glycerol, at an amount of 43 ml/l (that is to say 43 ml of glycerol per liter of water used in the preparation of hydrogel), and cured with: [0182] 3A: MgCl.sub.2, at an amount of 1 g/l (that is to say 1 g of MgCl.sub.2 per liter of water used in the preparation of the hydrogel) or [0183] 3B: MgSO.sub.4, at an amount of 1 g/l.

[0184] The gellan gum used here to prepare the sheets of dehydrated polysaccharide hydrogel is Gelrite, distributed by CARL ROTH GmbH, Germany.

[0185] Whether the curing agent is MgCl.sub.2 or MgSO.sub.4, the results obtained are very similar. The colonies of E. coli grow on the surface of the hydrogel sheet. They have a very good size and a very good staining. The morphotype thereof corresponds to that of colonies of E. coli growing on a reference chromogenic agar such as chromID CPS Elite.

[0186] FIG. 4 shows photographs of a culture and an isolation of E. coli conducted on a microbiological culture device, the sheet of dehydrated polysaccharide hydrogel of which was obtained from a 15 g/l gellan hydrogel, with a structure reinforced with glycerol, at an amount of 43 ml/l, and cured with CaCl.sub.2, at an amount of 1 g/l.

[0187] The gellan gum used here is Gelrite.

[0188] Compared to the previous examples, the colonies of E. coli appear to be smaller, with a slight diffusion of the staining at the edge.

[0189] FIG. 5 shows a photograph of cultures and isolations of E. coli conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 15 g/l gellan hydrogels, with a structure reinforced with glycerol, at an amount of 43 ml/l, and cured with: [0190] 5A: MgCl.sub.2, at an amount of 1 g/l, or [0191] 5B : MgCl.sub.2, at an amount of 5 g/l.

[0192] The gellan gum used here is Gelzan, distributed by CP KELCO, United States.

[0193] With 1 g/l of MgCl.sub.2, the colonies of E. coli growing at the surface of the hydrogel sheet have a very good size and a very good staining. The morphotype thereof corresponds to that of colonies of E. coli growing on a reference chromogenic agar such as chromID CPS Elite (FIG. 5, part 5C).

[0194] With 5 g/l of MgCl.sub.2, the colonies are smaller.

[0195] Without MgCl.sub.2, the colonies are very diffuse (FIG. 5, part 5D).

[0196] FIG. 6 shows photographs of cultures and isolations of E. faecalis conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 15 g/l gellan hydrogels, with a structure reinforced with glycerol, at an amount of 43 ml/l, and cured with: [0197] 6A: MgCl.sub.2, at an amount of 1 g/l. [0198] 6B: MgCl.sub.2, at an amount of 2 g/l, or [0199] 6C: MgCl.sub.2, at an amount of 5 g/l.

[0200] The gellan gum used here is Gelzan.

[0201] The colonies of E. faecalis growing at the surface of the hydrogel sheet are identical in size, color and morphotype to the colonies of E. faecalis growing on a reference chromogenic agar such as chromID CPS Elite.

[0202] FIG. 7 shows photographs of cultures and isolations of P. mirabilis conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 15 g/l gellan hydrogels, with a structure reinforced with glycerol, at an amount of 43 ml/l, and cured with: [0203] 7A: MgCl.sub.2, at an amount of 1 g/l. [0204] 7B: MgCl.sub.2, at an amount of 2 g/l, or [0205] 7C: MgCl.sub.2, at an amount of 5 g/l.

[0206] The gellan gum used here is Gelrite.

[0207] The colonies of P. mirabilis growing at the surface of the hydrogel sheet are identical in size, color and morphotype to the colonies of P. mirabilis growing on a reference chromogenic agar such as chromID CPS Elite.

[0208] FIG. 8 shows a photograph of cultures and isolations of E. coli conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 13 g/l or 15 g/l gellan hydrogels, with a structure reinforced with glycerol, at an amount of 43 ml/l and cured with CaCl.sub.2 used at 1 g/l or 2 g/l: [0209] 8A, 8A: 13 g/l gellan gum, 1 g/l CaCl.sub.2, [0210] 8B, 8B: 13 g/l gellan gum, 2 g/l CaCl.sub.2, [0211] 8C, 8C: 15 g/l gellan gum, 2 g/l CaCl.sub.1, [0212] 8D, 8D: 15 g/l gellan gum, 2 g/l CaCl.sub.2.

[0213] The gellan gum used here is Gelzan.

[0214] The four microbiological culture devices tested here give very similar results. Compared to the examples of FIG. 5, in which MgCl.sub.2 is used to cure the hydrogels, E. coli here forms colonies of slightly smaller size.

[0215] FIG. 9 shows a photograph of cultures and isolations of E. faecalis conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 15 g/l gellan hydrogels, with a structure reinforced with glycerol, at an amount of 43 ml/l, and cured with: [0216] 9A: 1 g/l CaCl.sub.2 [0217] 9B: 2 g/l CaCl.sub.2 [0218] 9C: 3 g/l CaCl.sub.2.

[0219] The gellan gum used here is Gelzan.

[0220] While the previous examples corresponding to FIG. 8 allow a prediction of a certain advantage in using MgCl.sub.2 rather than CaCl.sub.2 for the culture of E. coli, this observation is less obvious for the culture of E. faecalis.

[0221] FIG. 10 shows photographs of a culture and an isolation of E. coli conducted on a microbiological culture device, the sheet of dehydrated polysaccharide hydrogel of which was obtained from a 15 g/l gellan hydrogel, with a structure reinforced with glycerol, at an amount of 43 ml/l, and cured with MnCl.sub.2, at an amount of 1 g/l.

[0222] The gellan gum used here is Gelrite.

[0223] Compared to a culture of E coli on the reference medium chromID CPS Elite, the colonies of E. coli appear here to be smaller, but their staining is notably intensified by CaCl.sub.2.

[0224] FIG. 11 shows photographs of cultures and isolations of E. coli conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from polysaccharide hydrogels of various compositions: [0225] 11A.sub.1: 15 g/l gellan gum (more specifically Phytagel, distributed by Sigma Aldrich, United States), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0226] 11A.sub.2: 30 g/l gellan gum (Phytagel), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0227] 11B.sub.1: 25 g/l gellan gum (Gelrite), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0228] 11B.sub.2: 20 g/l gellan gum (Gelrite), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0229] 11B.sub.3: 8 g/l gellan gum (Gelrite), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0230] 11B.sub.4: 6 g/l gellan gum (Gelrite), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0231] 11C.sub.1: 20 g/l gellan gum (Gelzan), 43 ml/l glycerol, 1 g/1 MgCl.sub.2, [0232] 11C.sub.2: 8 g/l gellan gum (Gelzan), 43 ml/l glycerol, 1 g/l MgCl.sub.2, [0233] 11D.sub.1: 0.5 g/l xanthan gum, distributed by SIGMA ALDRICH, France, [0234] 11D.sub.2: 10 g/l xanthan gum [0235] 11E.sub.1, 11E.sub.1: 0.5 g/l potato starch, distributed by CARL ROTH GmbH, Germany. [0236] 11E.sub.2, 11E.sub.2: 15 g/l potato starch.

[0237] FIG. 12 shows photographs of cultures and isolations of E. coli conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from 15 g/l gellan hydrogels (in the case in point, Gelrite), cured with MgCl.sub.2 at an amount of 1 g/l and the structure of which was reinforced with glycerol at different concentrations: [0238] 12A: 32 ml/l [0239] 12B: 52 ml/l [0240] 12C: 62 ml/l

[0241] By increasing the glycerol concentration of the hydrogels, E. coli forms larger colonies, which nonetheless appear to be less protruding and more spread out on the hydrogel s.

[0242] FIG. 13 shows photographs of cultures and isolations of microorganisms conducted on microbiological culture devices, the sheets of dehydrated polysaccharide hydrogel of which were obtained from a 15 g/l Gelzan hydrogel, cured with MgCl.sub.2 at an amount of 1 g/l.

[0243] These microbiological culture devices were also successfully tested for the culture and detection of Streptococcus agalactiae (13A), Serratia marcescens, (13B), and for the co-culture and co-detection of S. marcescens and S. aureus (13C).