Which biochemical test is useful for differentiating Salmonella and Shigella from other Enterobacteriaceae?

Which biochemical test is useful for differentiating Salmonella and Shigella from other Enterobacteriaceae?

• A. Indole test
• B. Hydrogen sulfide production test
• C. Citrate utilization test
• D. Lactose fermentation test

Answer: (B)

The hydrogen sulfide production test is particularly useful for differentiating Salmonella and Shigella from other members of the Enterobacteriaceae family. Salmonella species are known for their ability to produce hydrogen sulfide (H2S) during their metabolism, which can be detected in culture media such as Triple Sugar Iron (TSI) agar, where black precipitates form due to the reaction of H2S with iron salts. In contrast, Shigella species do not produce hydrogen sulfide. This metabolic characteristic is a key factor that aids in the identification of these two genera, as it helps distinguish them from others that may ferment sugars or have different metabolic pathways. The indole test, while useful for identifying certain Enterobacteriaceae, does not specifically differentiate between Salmonella and Shigella. Similarly, the citrate utilization test assesses the ability to use citrate as a sole carbon source, which isn't a defining feature for these two genera. The lactose fermentation test typically serves to differentiate lactose fermenters from non-fermenters within the family but is less effective in discerning Salmonella or Shigella, especially since both are lactose non-fermenters. Thus, the hydrogen sulfide production test stands out as the most informative and practical test for this

The hydrogen sulfide production test is particularly useful for differentiating Salmonella and Shigella from other members of the Enterobacteriaceae family. Salmonella species are known for their ability to produce hydrogen sulfide (H2S) during their metabolism, which can be detected in culture media such as Triple Sugar Iron (TSI) agar, where black precipitates form due to the reaction of H2S with iron salts. In contrast, Shigella species do not produce hydrogen sulfide. This metabolic characteristic is a key factor that aids in the identification of these two genera, as it helps distinguish them from others that may ferment sugars or have different metabolic pathways.

The indole test, while useful for identifying certain Enterobacteriaceae, does not specifically differentiate between Salmonella and Shigella. Similarly, the citrate utilization test assesses the ability to use citrate as a sole carbon source, which isn't a defining feature for these two genera. The lactose fermentation test typically serves to differentiate lactose fermenters from non-fermenters within the family but is less effective in discerning Salmonella or Shigella, especially since both are lactose non-fermenters. Thus, the hydrogen sulfide production test stands out as the most informative and practical test for this