Which laboratory method is commonly used to detect Shiga toxin genes in Escherichia coli O157:H7?

Which laboratory method is commonly used to detect Shiga toxin genes in Escherichia coli O157:H7?

• A. PCR or immunoassay for Shiga toxin genes (stx).
• B. Gram stain.
• C. Catalase test.
• D. Oxidase test.

Answer: (A)

Detecting Shiga toxin genes is about confirming virulence at the genetic level. The best approach is a nucleic acid test that specifically looks for stx gene sequences. PCR for stx1 and stx2 is routinely used because it is fast, sensitive, and directly shows whether the strain carries the toxin genes. Immunoassays can detect the Shiga toxin protein itself, which signals toxin production but doesn’t prove the gene’s presence in the genome. Gram stain, catalase, and oxidase tests assess general cell features and metabolism, not toxin genes, so they don’t confirm stx.

Detecting Shiga toxin genes is about confirming virulence at the genetic level. The best approach is a nucleic acid test that specifically looks for stx gene sequences. PCR for stx1 and stx2 is routinely used because it is fast, sensitive, and directly shows whether the strain carries the toxin genes. Immunoassays can detect the Shiga toxin protein itself, which signals toxin production but doesn’t prove the gene’s presence in the genome. Gram stain, catalase, and oxidase tests assess general cell features and metabolism, not toxin genes, so they don’t confirm stx.