Question

1 Select all the key characteristics of a coliform

Group of answer choices

Small Gram negative rod

Contains spores

Ferments lactose in the presence of bile with acid and gas production

Does not contain spores

Produces gas in lauryl-tryptose broth

2 The coliform test consists of three parts: the presumptive test, the confirmed test, and the completed test. We perform all three of these in our teaching lab.

Group of answer choices

True

False

Answer 1

1.

• Coliform include fecal microorganisms, belonging to Enterobacteriaceae family.
• They are normal biota of gastrointestinal tract. Some of these microorganisms may contaminate water, through feces of humans and animals or sewage.
• Coliforms comprises of Gram Negative bacilli, which are non-spore forming bacteria.
• Coliforms have the ability to ferment lactose (in presence of bile salt, that inhibit Gram positive bacteria), to generate acid and gas.
• Lauryl Tryptose media selects Gram negative organisms like the coliforms, due to the presence of Sodium Lauryl Sulfate (inhibits Gram positive bacteria).
• The media also contain lactose. Thus, bacteria can ferment to produce gas.

Answer:

• Small Gram negative rod
• lactose in the presence of bile with acid and gas production
• Does not contain spores
• Produces gas in lauryl-tryptose broth

2. True

• MPN or most probable number is used for the determination of viable number of microorganisms in a diluted sample.
• The method is also called Poisson zeroes.
• The sample is diluted and tested for a specific positive result.
• The further dilution may lower the density of the organisms, such that there is no positive result for the test indicated.
• Microbiological MPN test uses presumptive, confirmative and completed test.
• It is mostly used for coliform analysis in water samples.