Detection of acid-producing bacteria
The disclosure provides culture devices and methods useful for detecting acid-producing bacteria in a sample. The devices include a nutrient medium and a pH indicator to detect and differentiate acid-producing microorganisms, such as lactic acid bacteria. Methods of use include detecting or enumerating acid-producing microorganisms. The methods further provide for the detection of gas-producing acid-producing bacteria.
1. A method comprising:
providing a thin film culture device comprising a culture medium to support growth of acid-producing bacteria and a cold water-soluble gelling agent, a carbohydrate that can be fermented by the acid-producing bacteria, a sample, and a pH indicator with a transition range that extends below pH 7.0;
combining, in the culture device, a predetermined volume of the sample,the culture medium, the pH indicator, and the fermentable carbohydrate;
incubating the culture device for a period of time; and
detecting the presence or absence of a microorganism;
wherein detecting the presence or absence of a microorganism comprises detecting the presence or absence of an acid-producing microorganism.
2. The method of claim 1 , wherein the pH of the culture medium in the provided thin film culture device is less than 6.5.
3. The method of claim 1 , wherein the provided thin film culture device further comprises a selective agent.
4. The method of claim 3 , wherein the selective agent is an antifungal agent.
5. The method of claim 4 wherein the antifungal agent is selected from the group consisting of Cycloheximide, Nystatin, Natamycin, Amphotericin B, Filipin, and combinations thereof.
6. The method of claim 1 , further comprising differentiating the acid-producing bacteria, wherein said differentiating comprises detecting production of carbon dioxide gas by individual colonies.
7. The method of claim 1 , wherein said incubating is carried out aerobically.
8. The method of claim 1 , wherein said incubating is carried out anaerobically.
9. The method of claim 1 , further comprising combining the sample with a diluent capable of neutralizing a chemical sanitizer.
10. The method of claim 1 , further comprising:
providing an imaging system; and
obtaining an image of a growth area of the culture device;
wherein said detecting comprises displaying, printing, or analyzing the image of the growth area.
11. The method of claim 10 , wherein the imaging system comprises an illumination source and wherein said obtaining comprises illuminating the growth area.
12. The method of claim 1 , further comprising the step of enumerating microorganisms.
13. The method of claim 12 , wherein said enumerating microorganisms comprises enumerating two or more types of microorganisms.
14. The method of claim 1 wherein the pH indicator is bromcresol purple, bromphenol blue, chlorophenol red, or bromcresol green.
15. The method of claim 1 wherein the acid-producing bacteria is Acetobacter or a lactic acid-producing bacteria.