Which of the following bacteria belong to the coliform group ? A. Escherichia coli B. Streptococcus faecalis C. Clostridium perfringens D. Bacillus Choose the correct answer from the options given below:
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In competitive exams, if the technically correct answer isn't an option, re-evaluate the question's potential context. Here, "coliform group" is likely used as a synonym for "fecal indicator group," which makes an otherwise incorrect option the best fit.
Step 1: Understanding the Concept:
The question asks to identify bacteria that belong to the "coliform group". This term can have a strict microbiological definition and a broader application in water quality testing, where it's often used interchangeably with "fecal indicator bacteria". Step 2: Detailed Explanation:
Strict Definition of Coliforms: Coliforms are defined as rod-shaped, Gram-negative, non-spore-forming, facultative anaerobic bacteria that ferment lactose with the production of acid and gas at 35-37°C.
A. {Escherichia coli:} Fits this definition perfectly and is the primary indicator of fecal contamination.
B. {Streptococcus faecalis (now {Enterococcus faecalis}):} Is Gram-positive and coccus-shaped. It is not a coliform by definition.
C. {Clostridium perfringens:} Is Gram-positive and forms spores. It is not a coliform.
D. {Bacillus:} Is a genus of Gram-positive, spore-forming rods. It is not a coliform.
Broader Context (Fecal Indicators): In many contexts, particularly older literature or applied environmental microbiology, the "coliform group" is discussed alongside other important indicators of fecal pollution.
A. {E. coli:} The classic fecal coliform.
B. {S. faecalis:} Used as an indicator of fecal pollution (fecal streptococci).
C. {C. perfringens:} Its spores can indicate past or remote fecal contamination due to their longevity.
Step 3: Analyzing the Options and Final Answer:
By the strict definition, only {E. coli} (A) is a coliform. However, there is no option for "A only". All options that include A also include other bacteria. This strongly suggests that the question is using a broader definition that encompasses key fecal indicator bacteria rather than adhering to the strict taxonomic/biochemical definition of coliforms. In this broader sense, {E. coli}, {S. faecalis}, and {C. perfringens} are all commonly monitored as indicators of fecal pollution. {Bacillus} species are generally environmental (soil) bacteria and not considered fecal indicators. Therefore, the most plausible intended answer is the group of common fecal indicator organisms.
This makes option (B) A, B, and C only, the best choice among the given alternatives.
