Shigella sonnei is differentiated from other Shigella species by which biochemical test?

Shigella sonnei is differentiated from other Shigella species by which biochemical test?

• A. ONPG positive
• B. Phenylalanine deaminase reaction
• C. Oxidase negative
• D. Motility at 22°C

Answer: (A)

Lactose utilization detected by the ONPG assay hinges on beta-galactosidase activity. Shigella sonnei uniquely shows beta-galactosidase activity among Shigella species, allowing lactose metabolism, whereas the other Shigella species typically do not. When the ONPG substrate is cleaved by beta-galactosidase, it turns yellow, indicating a positive result. This makes ONPG positivity the best way to distinguish Shigella sonnei from its relatives. Other options aren’t reliable differentiators for this species, since their biochemical traits (like oxidase status, motility, or phenylalanine deaminase) are not unique to S. sonnei.

Lactose utilization detected by the ONPG assay hinges on beta-galactosidase activity. Shigella sonnei uniquely shows beta-galactosidase activity among Shigella species, allowing lactose metabolism, whereas the other Shigella species typically do not. When the ONPG substrate is cleaved by beta-galactosidase, it turns yellow, indicating a positive result. This makes ONPG positivity the best way to distinguish Shigella sonnei from its relatives. Other options aren’t reliable differentiators for this species, since their biochemical traits (like oxidase status, motility, or phenylalanine deaminase) are not unique to S. sonnei.