Medical Laboratory Scientist (MLS) ASCP Practice Exam

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Which of the following is a key biochemical reaction for the identification of Enterobacteriaceae?

  1. Fermentation of proteins

  2. Reduction of sulfates to sulfides

  3. Reduction of nitrates to nitrites

  4. Absence of urease activity

The correct answer is: Reduction of nitrates to nitrites

The reduction of nitrates to nitrites is a crucial biochemical reaction used in the identification of Enterobacteriaceae. This reaction highlights the metabolic capability of these bacteria to utilize nitrates as an electron acceptor during anaerobic respiration. When nitrates are present, Enterobacteriaceae can reduce them to nitrites, which can be detected using specific reagents in a laboratory setting. A positive nitrate reduction test indicates the presence of this metabolic pathway, aiding in the differentiation among members of this family. The other options, while relevant in certain contexts, do not serve as primary indicators for identifying Enterobacteriaceae. For example, fermentation of proteins does not specifically distinguish this family and is more general to many organisms. The reduction of sulfates to sulfides is characteristic of sulfate-reducing bacteria, which are not limited to Enterobacteriaceae. Lastly, the absence of urease activity is not definitive for Enterobacteriaceae since not all members produce urease, and those that do may have varying urease activity. Thus, the reduction of nitrates to nitrites stands out as a key biochemical reaction for identification within this bacterial family.