Give an example of a non-lactose fermenting Enterobacteriaceae.

• A. Escherichia coli
• B. Salmonella spp.
• C. Klebsiella pneumoniae
• D. Citrobacter freundii

Answer: (B)

Salmonella spp. exemplifies a non-lactose fermenting member of the Enterobacteriaceae family. These bacteria are well-known for their ability to cause foodborne illnesses and their distinct laboratory identification traits. One key characteristic of Salmonella is its inability to ferment lactose, which is a critical factor in differentiating it from other members of the Enterobacteriaceae, such as Escherichia coli and Klebsiella pneumoniae, which are lactose fermenters.

In the laboratory, the capacity to ferment lactose can be tested using selective media, such as MacConkey agar, where lactose fermenters produce colored colonies. In contrast, Salmonella appears as colorless colonies on this medium, showcasing its non-lactose fermenting nature. This trait is significant in microbiological diagnostics and helps in the identification of pathogens within clinical and food safety settings.