Which key biochemical test differentiates Enterobacteriaceae from other Gram-negative bacilli?

Which key biochemical test differentiates Enterobacteriaceae from other Gram-negative bacilli?

• A. The oxidase test.
• B. The lactose fermentation test.
• C. The catalase test.
• D. The coagulase test.

Answer: (B)

The differentiation of Enterobacteriaceae from other Gram-negative bacilli is primarily based on their ability to ferment lactose. While there are several tests that can characterize different bacterial groups, the lactose fermentation test is particularly significant for Enterobacteriaceae. This family is known for its ability to ferment lactose, which can be observed in culture media such as MacConkey agar. Enterobacteriaceae, which includes genera such as Escherichia, Klebsiella, and Enterobacter, typically produce acid and gas from lactose, resulting in color changes on the media that indicate fermentation. In contrast, other Gram-negative bacilli, particularly non-lactose fermenters like Pseudomonas and Salmonella, do not produce acid from lactose and therefore do not yield the same results in this test. This capability makes lactose fermentation a vital differentiating characteristic for identifying Enterobacteriaceae in a clinical laboratory setting. Thus, using the lactose fermentation test is a reliable way to distinguish these bacteria from other groups of Gram-negative organisms.

The differentiation of Enterobacteriaceae from other Gram-negative bacilli is primarily based on their ability to ferment lactose. While there are several tests that can characterize different bacterial groups, the lactose fermentation test is particularly significant for Enterobacteriaceae. This family is known for its ability to ferment lactose, which can be observed in culture media such as MacConkey agar. Enterobacteriaceae, which includes genera such as Escherichia, Klebsiella, and Enterobacter, typically produce acid and gas from lactose, resulting in color changes on the media that indicate fermentation.

In contrast, other Gram-negative bacilli, particularly non-lactose fermenters like Pseudomonas and Salmonella, do not produce acid from lactose and therefore do not yield the same results in this test. This capability makes lactose fermentation a vital differentiating characteristic for identifying Enterobacteriaceae in a clinical laboratory setting. Thus, using the lactose fermentation test is a reliable way to distinguish these bacteria from other groups of Gram-negative organisms.