Method and apparatus for culturing with microbiological dry culture medium

Abstract

A device useful for growing aerobic microorganisms, particularly molds. The device employs a relatively small amount of water reconstitutable medium that can be sealed in order to prevent desiccation and contamination of the medium yet still provide an adequate supply of air to the medium, by the use of a membrane underlying the medium, to support the growth of aerobic microorganisms.

We claim: 
     
       1. A device for growing microorganisms, which device comprises a body member, which body member comprises (1) a waterproof substrate having a top surface and a bottom surface;   (2) an air-permeable membrane, having its peripheral edge(s) substantially uncovered, and having a top surface and a bottom surface, the bottom surface being fixed to and covering at least a portion of the top surface of the substrate; and   (3) cold-water-reconstitutable dry medium fixed to and covering at least a portion of the top surface of the membrane so as to define a growth region and comprising at least one ingredient selected from the group consisting of one or more gelling agents and one or more nutrients for growing microorganisms.   
     
     
       2. A device according to claim 1, wherein the air-permeable membrane is a microporous film or nonwoven web of synthetic or natural material. 
     
     
       3. A device according to claim 2, wherein the membrane is a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, nylon, polyvinylidine fluoride, rayon, and copolymers and blends thereof. 
     
     
       4. A device according to claim 1, wherein the membrane has a Gurley porosity value of less than about 100 seconds. 
     
     
       5. A device according to claim 1, wherein the membrane has a Gurley porosity value of less than about 50 seconds. 
     
     
       6. A device according to claim 1, wherein the membrane has a Gurley porosity value of less than about 25 seconds. 
     
     
       7. A device according to claim 1, wherein the membrane is between about 20 μm and about 100 μm thick. 
     
     
       8. A device according to claim 1, wherein the membrane is between about 40 μm and about 80 μm thick. 
     
     
       9. A device according to claim 1, further comprising cover means disposed adjacent to the dry medium and having a surface facing the dry medium, which cover means is substantially impermeable to microorganisms and water vapor and configured so as to cover at least the growth region. 
     
     
       10. A device according to claim 9, wherein the cover means is a cover sheet adhered in a hinge-like fashion along one edge of the body member. 
     
     
       11. A device according to claim 1, wherein the dry medium comprises a powder, and which device further comprises a layer of adhesive on at least said portion of the top surface of the membrane, the adhesive being insoluble in water and substantially non-inhibitory to the growth of the microorganisms, and wherein the powder is adhered substantially uniformly to the layer of adhesive. 
     
     
       12. A device according to claim 11, wherein the gelling agent is selected from the group consisting of locust bean gum, xanthan gum, and mixtures thereof. 
     
     
       13. A device according to claim 11, wherein the adhesive is a copolymer of 2-methylbutylacrylate and acrylic acid in a mole ratio of 90:10, respectively. 
     
     
       14. A device according to claim 11, wherein the layer of adhesive on the top surface of the membrane contains a dye that is metabolized by or otherwise reacts with microorganisms in order to cause the microorganisms to be colored or fluorescent. 
     
     
       15. A device according to claim 1, wherein the dry medium further comprises a bacteriostatic or bacteriocidal agent suitable to allow the growth of molds. 
     
     
       16. A device according to claim 9 additionally comprising a coating on the surface of the cover means facing the dry medium, which coating comprises (i) a layer of adhesive, which adhesive is insoluble in water and is substantially non-inhibitory to the growth of the microorganisms, and (ii) powder, which powder is cold-water-soluble and comprises at least one ingredient selected from the group consisting of one or more gelling agents and one or more nutrients for growing microorganisms, and which powder substantially uniformly adhered to the layer of adhesive on the cover sheet. 
     
     
       17. A device according to claim 1, wherein the dry medium comprises a coated medium. 
     
     
       18. A method of growing microorganisms comprising: (1) reconstituting the dry medium of the device according to claim 9 with an aqueous test sample containing microorganisms;   (2) placing the cover means over the reconstituted medium; and   (3) incubating the device at a suitable temperature and for a suitable time to allow the growth of microorganisms. .Iadd.   
     
     
       19.  A device for growing microorganisms, which device comprises a body member, which body member comprises (1) a waterproof substrate having a top surface and a bottom surface; (2) an air-permeable membrane, having its peripheral edge(s) substantially uncovered, and having a top surface and a bottom surface, the bottom surface being fixed to and covering a portion of the top surface of the substrate; and (3) reconstituted medium fixed to and covering at least a portion of the top surface of the membrane so as to define a growth region and comprising at least one ingredient selected from the group consisting of one or more gelling agents and one of more nutrients for growing microorganisms. .Iaddend. .Iadd.20. A device according to claim 19, further comprising cover means disposed adjacent to the medium and having a surface facing the medium, which cover means is substantially impermeable to microorganisms and configured so as to cover at the growth region. .Iaddend. .Iadd.21. A method of growing microorganisms comprising: (1) adding a sample containing microorganisms to the medium of a device according to claim 20 (2) placing the cover means over the hydrated medium; and (3) incubating the device at a suitable temperature and for a suitable time to allow the growth of microorganisms. .Iaddend.