METHOD, DEVICE, SENSOR CARTRIDGE AND KIT OF PARTS FOR CULTURING AND DETECTING MICROORGANISMS

Abstract

The invention relates to a method for culturing and detecting microorganisms, comprising the steps of providing a liquid sample (S) in a barrel (10) of a device (1) for culturing and detecting microorganisms, passing the liquid sample (S) through a first filtering membrane (40) such that microorganisms contained in the liquid sample (S) are retained at a first side (41) of the first filtering membrane (40), contacting said first side (41) with a first growth medium (210) capable of supporting growth of microorganisms, incubating the first filtering membrane (40) and the first growth medium (210) at an incubation temperature, arranging a sensing surface (51) of a gas sensor (50) in fluid connection with a second side (42) of the first filtering membrane (40), detecting a metabolic gas released by the microorganisms by means of the gas sensor (50). The invention further relates to a device (1) for culturing and detecting microorganisms, comprising a barrel (10) enclosing a barrel compartment (13) for receiving a liquid sample (S), a first piston (20) which (20) is movable in said barrel (10), wherein said barrel compartment (13) is configured to be brought in fluid communication via a first filtering membrane (40) with a sensing surface (51) of a gas sensor (50) configured to detect a metabolic gas released by microorganisms, wherein the first filtering membrane (40) is configured to retain microorganisms contained in the liquid sample (S) at the first side (41) of the first filtering membrane (40). Furthermore, a sensor cartridge (4) and a kit of parts comprising the device (1) are provided.

Claims

1. A method for culturing and detecting microorganisms, comprising the steps of a. providing a liquid sample (S) in a barrel (10) of a device (1) for culturing and detecting microorganisms, wherein said liquid sample (S) is particularly dispensed into said barrel (10) or aspirated into said barrel (10) via a first end opening (11) of said barrel (10), b. passing the liquid sample (S) through a first filtering membrane (40) from a first side (41) to a second side (42) of the first filtering membrane (40), the second side (42) being arranged opposite the first side (41), such that microorganisms contained in the liquid sample (S) are retained at the first side (41) of the first filtering membrane (40), c. contacting said first side (41) of the first filtering membrane (40) with a first growth medium (210) capable of supporting growth of microorganisms, d. incubating the first filtering membrane (40) and the first growth medium (210) at an incubation temperature, e. arranging a sensing surface (51) of a gas sensor (50) in fluid connection with the second side (42) of the first filtering membrane (40), f. detecting a metabolic gas released by the microorganisms by means of the gas sensor (50).

2. The method according to claim 1, wherein said first growth medium (210) is a solid, a gelified liquid or a liquid adsorbed into a porous solid or semi-solid, and wherein said device comprises a first piston (20) comprising a first tip (21), and wherein said first tip (21) of the first piston (20) comprises said first growth medium (210), wherein said first side (41) of said first filtering membrane (40) is contacted by said first growth medium (210) by moving said first piston (20) in said barrel (10) to a first position (101) along a longitudinal axis (L) of the barrel (10).

3. The method according to claim 2, wherein said first tip (21) of said first piston (20) comprises a first partial area (201) and a second partial area (202), the first partial area (201) and the second partial area (202) extending perpendicular to the longitudinal axis (L), wherein the first partial area (201) and the second partial area (202) are non-overlapping, and wherein said first growth medium (210) is arranged in or on the first partial area (201), and wherein a second growth medium (220) is arranged in or on the second partial area (202).

4. The method according to claim 1, wherein said first growth medium (210) is a liquid comprised in said liquid sample (S), and wherein the first side (41) of said first filtering membrane (40) is contacted by the first growth medium (210) upon providing said liquid sample (S) in said barrel (10) or by dispensing the liquid sample (S) through the first filtering membrane (40), wherein said liquid sample (S) is dispensed through the first filtering membrane (40) by moving the first piston (20) in the barrel (10) along the longitudinal axis (L) towards the filtering membrane (40) to a second position (102), wherein said first tip (21) of said first piston (20) is spaced apart from said first filtering membrane (40) in the second position (102), such that a volume of said liquid sample (S) comprising the liquid first growth medium (210) remains in the barrel (10) and contacts said first side (41) of said first filtering membrane (40).

5. The method according to claim 1, wherein said first growth medium (210) is contacted by a growth inhibitor (310) capable of inhibiting growth of microorganisms or a growth promotor (320) capable of promoting growth of microorganisms.

6. The method according to claim 5, wherein said growth inhibitor (310) or said growth promotor (320) is comprised in or on a second tip (31) of a second piston (30) of the device, and wherein said first growth medium (210) is contacted by said growth inhibitor (310) or said growth promotor (320) by moving said second piston (30) along said longitudinal axis (L) to a third position (103) in a bore (22) of said first piston (20).

7. The method according to claim 1, wherein the liquid sample (S) is incubated with magnetic beads carrying an affinity molecule on their surface, the affinity molecule being capable of specifically binding to microorganisms, wherein a suspension of the magnetic beads that have been incubated with the liquid sample (S) is provided in the barrel (10) of the device (1) for culturing and detecting microorganisms, wherein the first filtering membrane (40) comprises or consists of a magnetic material providing a magnetic force, and wherein the magnetic beads are precipitated on the first side (41) of the first filtering membrane (40) by the magnetic force.

8. A device (1) for culturing and detecting microorganisms, comprising a. a barrel (10) extending along a longitudinal axis (L) between a first end opening (11) and a second end opening (12), the barrel (10) enclosing a barrel compartment (13) for receiving a liquid sample (S), b. a first piston (20) comprising a first tip (21), wherein said first piston (20) is movable in said barrel (10) along the longitudinal axis (L) of the barrel (10), characterized in that said barrel compartment (13) is configured to be brought in fluid communication via a first filtering membrane (40) with a sensing surface (51) of a gas sensor (50) configured to detect a metabolic gas released by microorganisms, wherein the first filtering membrane (40) comprises a first side (41) and a second side (42) opposite the first side (41), wherein the first side (41) of the first filtering membrane (40) faces the barrel compartment (13) and the second side (42) of the first filtering membrane (40) faces the sensing surface (51), and wherein the first filtering membrane (40) is configured to retain microorganisms contained in the liquid sample (S) at the first side (41) of the first filtering membrane (40), particularly wherein the device (1) comprises said first filtering membrane (40) and/or said gas sensor (50).

9. The device (1) according to claim 8, characterized in that the first tip (21) of the first piston (20) comprises a first growth medium (210) capable of supporting growth of microorganisms, wherein said first piston (20) is movable along the longitudinal axis (L) in the barrel (10) to a first position (101), in which the growth medium (210) contacts the first side (41) of the first filtering membrane (40).

10. The device (1) according to claim 9, characterized in that said first tip (21) of said first piston (20) comprises a first partial area (201) and a second partial area (202), the first partial area (201) and the second partial area (202) extending perpendicular to the longitudinal axis (L), wherein the first partial area (201) and the second partial area (202) are non-overlapping, and wherein said first growth medium (210) is comprised in or on the first partial area (201), and wherein a second growth medium (220) is comprised in or on the second partial area (202).

11. The device (1) according claim 9, characterized in that the device (1) comprises at least one second piston (30) comprising a second tip (31), wherein said second piston (30) is movable along the longitudinal axis (L) in the barrel (10), particularly in a bore (22) of the first piston (20), to a third position (103), wherein the second tip (31) comprises or is configured to comprise a growth inhibitor (310) capable of inhibiting growth of microorganisms or a growth promotor (320) capable of promoting growth of microorganisms.

12. The device (1) according to claim 8, characterized in that the sensing surface (51) of said gas sensor (50) is arranged in a sensor compartment (57) which is in fluid connection with the second side (42) of the first filtering membrane (40), wherein said sensor compartment (57) comprises an inlet (52) and an outlet (53), wherein said inlet (52) comprises a first valve (54) allowing gas flow into the sensor compartment (57), and wherein the outlet (53) comprises a second valve (55) allowing gas flow out of the sensor compartment (57).

13. The device (1) according to claim 8, characterized in that the first filtering membrane (40) comprises or consists of a magnetic material providing a magnetic force, such that magnetic beads comprised in the liquid sample (S) can be precipitated on the first side (41) of the first filtering membrane (40) by the magnetic force.

14. A sensor cartridge (4) comprising a gas sensor (50) comprising a sensing surface (51) configured to detect a metabolic gas released by microorganisms, wherein the sensor cartridge (4) comprises a connection opening (4a) configured to be connected to the first end opening (11) of the barrel (10) of the device (1) according to claim 8.

15. A kit of parts (5) comprising a. the device (1) according to claim 8, b. a filtering cap (3) extending along a longitudinal axis (L) between a connection opening (3a) and a dispensing opening (3b), wherein the filtering cap (3) comprises a first filtering membrane (40) comprising a first side (40) facing the connection opening (3a) and a second side (42) opposite the first side (41), the second side (42) facing the dispensing opening (3b), wherein the filtering cap (3) is configured to be removably connected to the first end opening (11) of the barrel (10) of the device (1), such that a liquid sample (S) can be passed through the first filtering membrane (40) from the first side (41) to the second side (42) of the first filtering membrane (40) to retain microorganisms contained in the liquid sample (S) at the first side (41) of the first filtering membrane, wherein the dispensing opening (3b) of the filtering cap (3) is configured to be brought in fluid communication with a sensing surface (51) of a gas sensor (50) configured to detect a metabolic gas released by microorganisms, and c. a sensor cartridge (4) comprising a gas sensor (50) comprising a sensing surface (51) configured to detect a metabolic gas released by microorganisms, wherein the sensor cartridge (4) comprises a connection opening (4a) configured to be connected to the connection opening (3a) of the filtering cap (3), d. optionally, an aspiration cap (2) extending along a longitudinal axis (L) between a connection opening (2a) and an aspiration opening (2b) opposite the connection opening (2a), wherein the aspiration cap (2) is configured to be removably connected to the first end opening (11) of the barrel (10) of the device, such that a liquid sample (S) can be aspirated through the aspiration opening (2b) into the barrel compartment (13) of the device (1) when the first piston (20) of the device (1) is moved along the longitudinal axis (L) in the direction from the first end opening (11) towards the second end opening (12).

Description

[0153] Examples of the present invention are now explained by reference to the attached drawings, from which additional embodiments may be drawn. The following description is meant to elucidate the invention without limiting its scope.

[0154] FIG. 1 shows a schematic of an embodiment of the device for culturing and detecting microorganisms according to the invention;

[0155] FIG. 2 shows a detail of the device according to FIG. 1, where the second piston is in the third position;

[0156] FIG. 3 shows a detail of the first tip of the first piston of the device for culturing and detecting microorganisms according to an embodiment of the invention;

[0157] FIG. 4 shows a cross-sectional view of an embodiment of the device for culturing and detecting microorganisms according to the invention;

[0158] FIG. 5 shows an aspiration cap (A), a filtering cap (B) and a device for culturing and detecting microorganisms (C) according to the invention, which constitute components of a kit of parts according to the invention;

[0159] FIG. 6 shows exemplary steps of the method according to an embodiment of the invention, wherein (A) depicts an aspiration step, (B) depicts a filtering step, and (C) depicts an incubation and detection step;

[0160] FIG. 7 shows an embodiment of a device for culturing and detecting microorganisms according to the invention comprising a removable sensor cartridge, wherein (A) shows the sensor cartridge, (B) shows the barrel of the device, and (C) shows the assembled device with the sensor cartridge connected to the barrel;

[0161] FIG. 8-9 show a perspective view (FIG. 8) and a cross-sectional view (FIG. 9) of an apparatus comprising a plurality of devices for culturing and detecting microorganisms according to the invention;

[0162] FIG. 10-11 show data representing the growth of microorganisms measured with a device for culturing and detecting microorganisms according to the invention.

[0163] FIG. 1 shows in a schematic cross-sectional view, a device 1 for culturing and detecting microorganisms comprising a barrel 10 for receiving a liquid sample S, wherein the barrel 10 extends along a longitudinal axis L between a first end opening 11 and a second end opening 12 disposed opposite of the first end opening 11. The barrel 10 comprises a peripheral wall delimiting a barrel compartment 13 (not shown in FIG. 1, see FIG. 2A), wherein the first end opening 11 and the second end opening 12 connect the barrel compartment 13 to the exterior of the device 1. The device 1 has a cylindrical shape with the longitudinal axis L being the central cylinder axis. The first end opening 11 is comprised in a nozzle 14, and the second end opening 12 is closed by a first piston 20 which is inserted into the barrel compartment 13. The device 1 further comprises a filtering membrane 40, which extends perpendicular to the longitudinal axis L. The filtering membrane 40 comprises a first side 41 facing the barrel compartment 13 and a second side 42 opposite the first side 41 (see also FIG. 2A for the arrangement of the first side 41 and the second side 42 relative to the barrel compartment 13) and facing the first end opening 11 at the end of the nozzle 14. The filtering membrane 40 is from a woven or non-woven material having a pore size (e.g. an average pore size) of 1 μm or less, such that most microorganisms are unable to pass the filtering membrane 40 between the first side 41 and the second side 42 and vice versa.

[0164] The device 1 further comprises a first piston 20 (also termed outer piston herein) which is movably arranged along the longitudinal axis L in the barrel compartment 13. The first piston 20 comprises a first tip 21. Furthermore, the first piston 20 may comprise a sealing ring 23 adjacent to the first tip 21, the first sealing ring 23 being in contact with an inner wall of the barrel 10, such that the interface between the first sealing ring 23 and the barrel 10 is liquid and/or gas tight. In this case the first piston 20 may be used to aspirate liquid from the first end opening 11 by moving, e.g. pulling, the first piston 20 towards the second end opening 12, and dispense liquid from the first end opening 11 by moving, e.g. pushing, the first piston 20 towards the first end opening 11.

[0165] The first tip 21 of the first piston 20 comprises a first growth medium 210, on which microorganisms of interest, which are to be cultured and detected by the device 1, can grow. In other words, the first medium 210 is a solid, a gelified liquid or a liquid adsorbed into a porous solid or semi-solid that is attached to the first tip 21. For example, the first growth medium 210 may be a nutrient agar pad which coats the first tip 21 or is otherwise attached to the first tip 21. In one embodiment, the first tip 21 may comprise a recess, into which heated nutrient agar is poured or dispensed and solidified by cooling, after which the agar pad stays attached to the bottom and side walls of the recess. The first piston 20 and the first growth medium 210 are configured and arranged in a manner such that the first growth medium 210 contacts the first side 41 of the filtering membrane 40 in a first position 101 (as depicted in FIG. 1). That means that the first piston 20 has an appropriate length, such that the first tip 21 is able to touch the filtering membrane 40 in the first position 101, and the first growth medium 210 protrudes from the first tip 21 in the direction along the longitudinal axis L. In particular, the first piston 20 comprises a bore 22 or a plurality of bores 22 (in case a plurality of second pistons 30 is to be used) extending along the longitudinal axis L for receiving a second piston 30 or a plurality of second pistons 30.

[0166] FIG. 1 shows an embodiment, where one second piston 30 comprising a second tip 31 is movably arranged along the longitudinal axis L relative to the first piston 20 in the bore 22 of the first piston 20. Alternatively, a plurality of second pistons 30 comprising respective second tips 31 may be arranged in the bore 22 of the first piston 30 (not shown). These may be movable along the longitudinal axis L in the bore independently of each other or together.

[0167] FIG. 2 A-B illustrates the motion of the first piston 20 in the barrel compartment 13 of the barrel 10, and FIG. 2 C-D show the motion of the second piston 30 in the bore 22 of the first piston 20 during steps of the method according to the invention.

[0168] The first piston 20 is moved downwards (indicated by the arrow in FIG. 2A) from the position above the first filtering membrane 40 shown in FIG. 2A to the first position 101 shown in FIG. 2B, where the first growth medium 210 at the first tip 21 of the first piston 20 contacts the first side 41 of the first filtering membrane 40. In this manner, microorganisms on the first side 41 of the first filtering membrane 40 are contacted by the first growth medium 210, such that they can grow.

[0169] Subsequently, as shown in FIGS. 2C and 2D, a second piston 30 is moved downwards (indicated by the arrow in FIG. 2C, such that a second tip 31 of the second piston 30 contacts a surface 211 (opposite the first filtering membrane 40) of the growth medium 210 from inside the bore 22 of the first piston 20 (third position 103 in FIG. 2D). Thereby, a growth inhibitor 310 or a growth promotor 320 disposed at the second tip 31 contacts the first growth medium 210, such that the growth inhibitor 310 or growth promotor 320 can diffuse into the growth medium 210 to inhibit or promote growth of the microorganisms. The growth inhibitor 310 or growth promotor 320 may be provided on the second tip 31 of the second piston 30 in solid, semi-solid or gelified form, i.e. the second tip 31 is coated with the growth inhibitor 310 or growth promotor 320 or the growth inhibitor 310 or growth promotor 320 is attached to the second tip 31. In particular, the growth inhibitor 310 may be an antibiotic provided in a diffusion disk connected to the second tip 31 of the second piston 30.

[0170] The downward movement of the second piston 30 may be performed repeatedly to increase the amount of growth inhibitor 310 or growth promotor 320 gradually in a “bolus per bolus” manner.

[0171] As depicted in FIG. 2, the first piston 20 and the second piston 30 are configured such that the second tip 31 of the second piston 30 is able to contact the surface 211 of the first growth medium 210 opposite from the filtering membrane 40 (the upper surface in FIGS. 1 and 2). Thus, this surface 211 is accessible from the bore 22 of the first piston 20, and the second piston 30 has sufficient length and dimensions, such that the second tip 31 of the second piston 30 is able to touch this surface 211. Depending on the dimensions and the force of the downward movement, the second tip 31 may produce a groove 212 in the first growth medium 210.

[0172] According to an alternative embodiment (not shown), the second piston 30 may be moved towards the second end opening 12 to a third position 103 above the surface 211. Subsequently, for example, a liquid growth inhibitor 310 or liquid growth promotor 320 may be dispensed onto the surface 211, e.g. from a reservoir in the second piston 30 or from a separate source.

[0173] FIGS. 1 and 2 and 4 show just one second piston 30 arranged in the bore 22 of the first piston 20. However, a plurality of second pistons 30 can be arranged, e.g. parallel to each other along the longitudinal axis L, in the bore 22 of the first piston 20. For example, the same growth inhibitor 310 or growth promotor 320 may be added to the first growth medium 210 by sequentially moving the second pistons 30 gradually increase the amount of growth inhibitor 310 or growth promotor 320. Alternatively, the individual second pistons 30 may contain different kinds of growth inhibitors 310 and/or growth promotors 320, and the first growth medium 210 may be subjected to these substances sequentially.

[0174] As depicted in FIG. 3, which shows the first tip 21 of the first piston 20 in a cross-sectional view perpendicular to the longitudinal axis L depicted in FIGS. 1 and 4, it is also possible within the scope of the invention to provide a plurality of different growth media on the first tip 21 of the first piston 20. This may be achieved by coating a plurality of separate partial areas of the first tip 21 with different growth media (i.e. containing different nutrient compositions, different additives or the like). FIG. 3 shows an example where the tip 21 is divided in eight separate partial areas 201, 202, 203, 204, 205, 206, 207, 208, wherein the first partial area 201 contains the first growth medium 210 and the second partial area 202 contains a second growth medium 220. The other partial areas may contain either the first or the second growth medium, or further different growth media.

[0175] It should be noted that all embodiments described above with reference to the first growth medium 210 may equally or analogously applied to the second growth medium 220 and any additional further growth medium. This applies, in particular, to providing growth inhibitors 310 and/or growth promotors 320 to the first growth medium 210 by means of one or several second pistons 30. For example, the first piston 20 with the first tip 21 depicted in FIG. 3 could contain eight or more second pistons 30 in its bore 22 which are configured to supply growth inhibitors 310 or growth promotors 320 to the growth media in the partial areas 201, 202, 203, 204, 205, 206, 207, 208.

[0176] FIG. 1 further shows a gas sensor 50 comprising a sensing surface 51 capable of detecting a metabolic gas produced during growth of microorganisms. The gas sensor 50 further comprises a sensor compartment 57, in which the sensing surface 51 is arranged, and which is in fluid connection with the second side 42 of the filtering membrane 40 of the device 1, such that metabolic gases can diffuse from the first side 41 of the filtering membrane 40, where the microorganisms are growing, through the filtering membrane 40 into the sensor compartment 57. In other words, the filtering membrane 40 and the gas sensor 50 have a shared headspace.

[0177] FIG. 4 shows a cross-sectional view of a further embodiment of the device 1 comprising analogous components to the device 1 shown in FIG. 1 as well as additional optional details, which are not shown in FIG. 1. The device 1 is depicted in the configuration, where the first growth medium 210 at the first tip 21 of the first piston 20 contacts the first filtering membrane 40, and the growth inhibitor 310 or growth promotor 320 at the second tip 31 of the second piston 30 contacts the first growth medium 210.

[0178] According to the embodiment of FIG. 4, the second piston 30 fills substantially the entire bore 22 of the first piston 20.

[0179] The first piston 20 according to the embodiment of FIG. 4 comprises a first sealing ring 23 which seals the first piston 20 against the inner wall of the barrel 10. Furthermore, in this embodiment, the second piston 30 comprises a second sealing ring 32 abutting the inner wall of the bore 22 of the first piston 20, thereby sealing the second piston 30 against the first piston 20.

[0180] Further, in the embodiment of FIG. 4, the second piston 30 comprises an inner bore 33 which reduces the weight of the second piston 30. This is especially advantageous if the second piston 30 is made from a relatively heavy material, such as a metal.

[0181] The gas sensor 50 of the device 1 according to the embodiment shown in FIG. 4 comprises a sensor compartment 57 enclosed by a casing 59. The casing 59 comprises an opening for insertion of the nozzle 14 of the barrel 10. The opening of the casing 59 is connected to the sensor compartment 57, and a third sealing ring 16 on the casing 59 is configured to seal the sensor compartment 57 against the nozzle 14 when the nozzle 14 is inserted into the opening as shown in FIG. 4. A sensing surface 51 of the gas sensor 50 is arranged in the sensor compartment 57 and connected to a printed circuit board 58 comprising electronic components of the gas sensor 50.

[0182] FIGS. 5 and 6 show a further embodiment of the device 1, where the filtering membrane 40 is provided in a separate removable filtering cap 3 (FIG. 5 B) and an additional aspiration cap 2 (FIG. 5 A) is provided, e.g. in a kit of parts 5. The depicted embodiment of the device 1 comprises two separate parallel barrels 10 and two associated first pistons 20. However, the illustrated principle may also be equally applied to embodiments with only one barrel 10 and one first piston 20 (e.g. FIGS. 1 and 4) or more than two barrels 10 and first pistons 20 (e.g. FIGS. 8 and 9).

[0183] The aspiration cap 2 shown in FIG. 5 A comprises connection openings 2a configured to be releasably connected to the respective first end openings 11 of the device 1 depicted in FIG. 5 C. Furthermore, the aspiration cap 2 comprises aspiration openings 2b for aspirating a liquid opposite of the connection openings 2a. The aspiration openings 2b are arranged on nozzles 14.

[0184] The filtering cap 3 shown in FIG. 5 B comprises connection openings 3a configured to be releasably connected to the respective first end openings 11 of the device 1 depicted in FIG. 5 C. Furthermore, the filtering cap 3 comprises dispensing openings 3b opposite the connection openings 3a, and filtering membranes 40 separating the filtering cap 3 in compartments facing the dispensing openings 3b and the connection openings 3a. Therein, the first side 41 of the filtering membranes 40 faces the respective connection opening 3a and the second side 42 of the filtering membranes 40 faces the respective dispensing opening 3b.

[0185] FIG. 6 illustrates an embodiment of the method according to the invention using the components shown in FIG. 5 A to C. In the step shown in FIG. 6 A, the connection openings 2a of the aspirating cap 2 are connected to the respective first end openings 11 of the device 1 (see FIG. 5), and the nozzles 14 comprising the aspiration openings 2b are placed below the surface of a liquid sample S contained in a receptacle 70. Thereafter, the first pistons 20 are moved towards the second end opening 12 of the device 1 (upwards in FIG. 6 A) to aspirate the liquid sample S into the barrel compartments 13 of the barrels 10. When a desired volume of the liquid sample S has been loaded into the barrel compartments 13, the aspiration cap 2 is removed, and a filtering cap 3 (se FIG. 5 B) is connected to the barrel 10 by connecting the connection openings 3a of the filtering cap 3 to the first end openings 11 of the barrel 10.

[0186] Subsequently, as depicted in FIG. 6 B, the liquid sample S is filtered by the filtering membranes 40 in the filtering cap 3 by moving the first piston 20 towards the first end openings 11 of the barrel 10. Consequently, microorganisms in the liquid sample S are retained on the first side 41 of the filtering membrane 40.

[0187] In one embodiment, the first tip 21 of the first piston 20 is advanced to the first position 101, where the first tip 21 contacts the first side 41 of the filtering membrane 40. Thereby, in particular, a solid first growth medium 210 on the first tip 21 (not shown in FIG. 6) may be brought in contact with the filtering membrane 40.

[0188] Alternatively, if the first growth medium 210 is a liquid contained in the liquid sample S, the first tip 21 is advanced to the second position 102, where the first tip 21 is spaced apart from the filtering membrane 40. In this manner, a volume of the liquid sample S remains in the barrel compartment 13.

[0189] In both cases, the filtered liquid is particularly discarded.

[0190] FIG. 6 C depicts an incubation and detection step, where the device 1 is placed in an incubator 80 configured to heat the device 1 to a desired incubation temperature suitable to allow growth of the microorganisms of interest, e.g. 37° C. The first end openings 11 of the device 1 are respectively connected to a first gas sensor 50a and a second gas sensor 50b to detect metabolic gases produced by the growing microorganisms on the first side 41 of the filtering membranes 40 and/or in the first growth medium 210. The gas sensors 50a, 50b each have a shared headspace with the respective second side 42 of the respective first filtering membrane 40, such that the metabolic gases diffuse to the respective sensing surface 51 (not shown in FIG. 6, see FIGS. 1 and 4) of the respective gas sensor 50a, 50b without the danger of microorganisms contaminating the gas sensors 50a, 50b.

[0191] FIG. 7 A-C show an embodiment of the device 1 for culturing and detecting microorganisms, where the gas sensor 50 is comprised in a sensor cartridge 4 which is removably connected to the first end opening 11 of the device 1. FIG. 7A shows the disconnected sensor cartridge 4 comprising the connection opening 4a. FIG. 7B schematically depicts the barrel 10 of the device with the first end opening 11 and the second end opening 12 and the first filtering membrane 40. In FIG. 7C, the assembled device 1 is shown, wherein the connection opening 4a of the sensor cartridge 4 has been connected to the first end opening 11 of the barrel 10, e.g. by a plug-in connection. In FIGS. 7B and 7C, only the barrel 10 and the first filtering membrane 40 of the device 1 are shown for simplicity. Of course, a first piston 20 and an optional second piston 30 similar to those shown in FIGS. 1 and 4 may be provided in the barrel compartment 13 of the device 1 shown in FIG. 7.

[0192] The gas sensor 50 comprises a sensor compartment 57, in which a sensing surface 51 is arranged. The sensor compartment 57 is delimited by a second filtering membrane 60, providing an additional barrier against contamination of the sensor compartment 57, the second filtering membrane 60 having a first side facing the sensor compartment 57 and a second side facing the outside of the sensor cartridge 4.

[0193] When the sensor cartridge 4 and the device 1 are assembled, an intermediate compartment 15 is formed between the second side 42 of the first filtering membrane 40 and the second side of the second filtering membrane 60.

[0194] Metabolic gases produced by microorganisms growing on the first side 41 of the first filtering membrane 40 diffuse through the first filtering membrane 40 into the intermediate compartment 15 and subsequently through the second filtering membrane 60 into the sensor compartment 57, where the metabolic gases can be detected at the sensing surface 51.

[0195] In addition, the gas sensor 50 shown in FIG. 7 comprises an inlet 52 and an outlet 53 connecting the sensor compartment 57 to the exterior of the gas sensor 50. The inlet 52 comprises a first valve 54, e.g. a check valve, allowing gas flow into the sensor compartment 57, and the outlet 53 comprises a second valve 55, e.g. a check valve, allowing gas flow out of the sensor compartment 57. Seals 56, such as sealing rings, are arranged at the interface of the inlet 52 and the wall delimiting the sensor compartment 57 and at the interface of the outlet 53 and the wall delimiting the sensor compartment 57, providing a gas-tight seal.

[0196] The sensor compartment 57 may be flushed with a desired flushing gas through the inlet 52 and the outlet 53. For example, before usage of the gas sensor 50, one or more calibrant gases may be fed into the inlet 52 and removed from the outlet 53 of the sensor compartment 57 as a steady state flow. Furthermore, in the idle state of the gas sensor 50, the sensor compartment 57 may be flushed with an air flow, e.g. at 95% relative humidity and the desired culturing temperature (e.g. 37° C.). For instance, the air flow may consist of ‘zero air’ or at least a N.sub.2/O.sub.2 mixture or ambient air, from which volatile organic compounds have been removed. In particular, the term ‘zero air’ as used herein refers to air with a concentration of 0.05 ppm or less of organic compounds. Thereby, the baseline of the gas sensor 50 may be adjusted before it is exposed to the growing culture of microorganisms. This improves sensitivity.

[0197] The above-described functionality may also be embodied in a gas sensor 50 which is not comprised in a removable sensor cartridge 4. That is, such a gas sensor 50 may comprise an inlet 52 comprising a first valve 54, e.g. a check valve, allowing gas flow into the sensor compartment 57, and an outlet 53 comprising a second valve 55, e.g. a check valve, allowing gas flow out of the sensor compartment 57.

[0198] FIGS. 8 and 9 show different views of an apparatus 6 comprising a plurality of devices 1 arranged in parallel to each other to form a two-dimensional array. In particular, the devices 1 are formed and configured as the device 1 shown in FIG. 4. In particular, each device comprises a barrel 10, a first piston 20, a second piston 30, a first filtering membrane 40 and a gas sensor 50 in fluid connection with the second side 42 of the respective first filtering membrane 40. FIG. 8 shows a perspective, cut-away view of the apparatus 6 and FIG. 9 is a cross-sectional view through one row of four devices 1. Such an apparatus 6 has the advantage that several liquid samples S may be tested for microorganisms in parallel. Using the apparatus 6, it is also possible to test microorganisms in a liquid sample S for resistance and susceptibility to a number of different growth inhibitors, such as antibiotics.

[0199] FIGS. 10 and 11 show data obtained with a device 1 according to the invention. The plots shown in FIG. 10 were obtained by culturing microorganisms from three different patient samples suffering from a urinary tract infection: the analyzed urine sample of patient 1 had a high bacterial load of bacteria resistant to a certain antibiotic (trace 1004), the urine sample from patient 2 had a high bacterial load of bacteria susceptible to the antibiotic (trace 1005), and the urine sample of patient 3 had a low bacterial load of bacteria susceptible to the antibiotic (trace 1006).

[0200] The start of the experiment is indicated by the arrow 1001. Arrows 1002 indicate cultures without addition of the antibiotic, whereas arrows 1003 indicate cultures to which the antibiotic was added at the start 1001 of the experiment. The x-axis of the plot in FIG. 10 shows time in hours after the start 1001 of the experiment and the y-axis displays the signal of the gas sensor 50 of the device 1 in arbitrary units (a.u.).

[0201] It can be observed from FIG. 10 that without antibiotics in case of the resistant high bacterial load sample 1004 and the susceptible high bacterial load sample 1005, the amount of metabolic gases detected by the gas sensor 50 sharply rises to 2000 a.u. after about 1 hour from the start 1001 of the experiment. The low bacterial load susceptible sample 1006 gives rise to the same gas sensor 50 signal after about 5.5 h.

[0202] A marked difference is observed in the presence of antibiotics. Whereas the resistant high bacterial load sample 1004 displays a sharp increase of the gas sensor 50 signal lagging behind the signal without antibiotics by about 0.5 h, no increase of the gas sensor 50 signal is observed for the high bacterial load susceptible sample 1005 and the low bacterial load susceptible sample 1006, which remain slightly above baseline after 6 h.

[0203] This shows that the response of bacterial cultures to antibiotics can be accurately traced by the device 1 according to the invention.

[0204] FIG. 11 shows a plot of E. coli concentration in colony forming units from automatic growth detection 1102 against detection time in hours. The indicated colony forming units have been determined at the start of the experiment. An exponential fit 1101 and the WHO infection border 1103 are indicated. For example, automatic growth detection may be performed by analyzing the relative level, the slope and/or the curvature of the traces shown in FIG. 10 after normalization of the data against the baseline.

TABLE-US-00001 List of reference numerals 1 Device for culturing and detecting microorganisms 2 Aspiration cap 2a Connection opening of aspiration cap 2b Aspiration opening 3 Filtering cap 3a Connection opening of filtering cap 3b Dispensing opening 4 Sensor cartridge 4a Connection opening of sensor cartridge 5 Kit of parts 6 Apparatus 10 Barrel 11 First end opening 12 Second end opening 13 Barrel compartment 14 Nozzle 15 Intermediate compartment 16 Third sealing ring 20 First piston 21 First tip 22 Bore 23 First sealing ring 30 Second piston 31 Second tip 32 Second sealing ring 33 Bore 40 First filtering membrane 41 First side of first filtering membrane 42 Second side of first filtering membrane 50 Gas sensor 50a First gas sensor 50b Second gas sensor 51 Sensing surface 52 Inlet 53 Outlet 54 First valve 55 Second valve 56 Seal 57 Sensor compartment 58 Printed circuit board 59 Casing 60 Second filtering membrane 70 Receptacle 80 Incubator 101 First position 102 Second position 103 Third position 201 First partial area 202 Second partial area 203, 204, 205, 206, 207, 208 Further partial areas 210 First growth medium 211 Surface of first growth medium 212 Opening 310 Growth inhibitor 320 Growth promotor 1001 Start of measurement 1002 Measurement without growth inhibitor 1003 Measurement with growth inhibitor 1004 Resistant microorganisms-high bacterial load 1005 Susceptible microorganisms-high bacterial load 1006 Susceptible microorganisms-low bacterial load 1101 Exponential fit 1102 Automatic growth detection 1103 WHO infection border L Longitudinal axis S Liquid sample