Why Might a Large Number of Competing Microorganisms in a Food

question 34

Multiple Choice

Why might a large number of competing microorganisms in a food sample result in lack of sensitivity of culture methods for detecting pathogens?

• A) Many microbes secrete compounds that can be toxic for their competitors. If you need a pathogenic microbe to grow in a culture in order to detect it, these toxic compounds might inhibit the growth of the pathogen and impede the test.
• B) You can't obtain a pure culture from a food sample that has a large number of microbes present. It would be impossible to detect only one from within the sample.
• C) Culture methods often rely on biochemical changes taking place in medium for identification. With multiple microbes present, you may not be sure that the biochemical change observed is from the presence of a pathogen or from some other non-dangerous bacterium that also induces the biochemical change.
• D) The sheer number of microbes present might shut down the growth/replication of a pathogenic microbe in a food sample due to a "starving out" effect. If it can't grow/replicate, it won't be detectable by a culturing method test.
• E) Many microbes secrete compounds that can be toxic for their competitors. If you need a pathogenic microbe to grow in a culture in order to detect it, these toxic compounds might inhibit the growth of the pathogen and impede the test AND culture methods often rely on biochemical changes taking place in medium for identification. With multiple microbes present, you may not be sure that the biochemical change observed is from the presence of a pathogen or from some other non-dangerous bacterium that also induces the biochemical change.

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