If Shigella or Salmonella is suspected in a stool specimen, in what transport medium should it be sent?

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Multiple Choice

If Shigella or Salmonella is suspected in a stool specimen, in what transport medium should it be sent?

The key idea is to preserve the pathogens while limiting the growth of the normal stool flora during transport. Cary-Blair transport medium is a semi-solid, buffered medium designed for enteric pathogens. Its buffering helps maintain a stable pH, and its low nutrient content slows down nonpathogenic bacteria, so Shigella and Salmonella stay viable without being outcompeted. This improves the chance of recovering these pathogens when the specimen is cultured at the lab. Other options don’t serve this purpose well. Buffered saline and direct send don’t suppress normal flora, so pathogenic organisms can be masked by faster-growing bacteria. Saline with fixative would fix organisms and prevent subsequent culture growth, making it unsuitable for isolation.

The key idea is to preserve the pathogens while limiting the growth of the normal stool flora during transport. Cary-Blair transport medium is a semi-solid, buffered medium designed for enteric pathogens. Its buffering helps maintain a stable pH, and its low nutrient content slows down nonpathogenic bacteria, so Shigella and Salmonella stay viable without being outcompeted. This improves the chance of recovering these pathogens when the specimen is cultured at the lab.

Other options don’t serve this purpose well. Buffered saline and direct send don’t suppress normal flora, so pathogenic organisms can be masked by faster-growing bacteria. Saline with fixative would fix organisms and prevent subsequent culture growth, making it unsuitable for isolation.

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