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 of detecting acid-producing bacteria, comprising:
providing a thin film culture device comprising a cold water-soluble gelling agent, a culture medium to support the growth of lactic acid bacteria, a pH indicator with a transition range that extends below pH 7.0, a carbohydrate that can be fermented by acid-producing bacteria, and a sample suspected of containing acid producing bacteria;
combining a predetermined volume of sample and the culture medium to form a first mixture;
combining, in the culture device, the first mixture, 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 incubating the culture device comprises incubating the device aerobically;
wherein detecting the presence of a microorganism comprises differentiating a microorganism;
wherein differentiating a microorganism comprises detecting a gas bubble associated with the microorganism.
2. The method of claim 1 , wherein differentiating a microorganism comprises detecting a pH indicator reaction.
3. The method of claim 1 , wherein the pH indicator is selected from the group consisting of bromcresol purple, chlorophenol red, bromcresol green, and bromphenol blue.
4. The method of claim 1 , further comprising combining the sample with a diluent capable of neutralizing a chemical sanitizer.
5. The method of claim 1 , wherein the pH of the culture medium is adjusted to a pH below 6.5 and wherein detecting the presence or absence of an acid producing microorganism.
6. The method of claim 1 , wherein incubating the culture device comprises incubating the device anaerobically.
7. The method of claim 1 , further comprising:
providing an imaging system; and
obtaining an image of a growth area of the culture device;
wherein detecting the presence or absence of a microorganism comprises displaying, printing, or analyzing the image of the growth area.
8. The method of claim 1 , further comprising the step of enumerating microorganisms.
9. The method of claim 1 , wherein providing a pH indicator with a transition range that extends below pH 7.0 comprises providing a liquid solution comprising the pH indicator.
10. The method of claim 7 , wherein the imaging system comprises an illumination source and wherein obtaining an image of the growth area comprises illuminating the growth area.
11. The method of claim 7 , further comprising the step of providing an image analysis system; wherein analyzing the image comprises analyzing the image with the image analysis system.
12. The method of claim 8 , wherein enumerating microorganisms comprises enumerating two or more types of microorganisms.