Which genera of Enterobacteriaceae are usually nonmotile at 36°C?

• A. Shigella, Klebsiella, and Yersinia
• B. Escherichia, Edwardsiella, and Enterobacter
• C. Proteus, Providencia, and Salmonella
• D. Serratia, Morganella, and Hafnia

Answer: (A)

The genera Shigella, Klebsiella, and Yersinia are recognized for their nonmotility at 36°C, which is a common characteristic within the Enterobacteriaceae family. Shigella species lack flagella and are known for causing bacillary dysentery, while Klebsiella species also do not exhibit movement due to the absence of flagella, instead being well-known pathogens associated with pneumonia and other infections. Yersinia, particularly the species Yersinia pestis, is historically significant for being the causative agent of the plague, and it is also nonmotile at this temperature due to its structure and environmental adaptations.

The other genera listed in the other options typically display motility. For instance, Escherichia and Enterobacter are generally motile due to their flagellar presence, which contributes to their movement in liquid media. Similarly, Proteus and Salmonella are well-known for their motility, utilizing their flagella effectively for movement. The grouping of Serratia, Morganella, and Hafnia also tends to include species that are motile.

Thus, the identification of Shigella, Klebsiella, and Yersinia as nonmotile at 36°C correctly aligns with