Which method is used to identify Salmonella, Shigella, and Streptococcus by detecting surface antigens?

Which method is used to identify Salmonella, Shigella, and Streptococcus by detecting surface antigens?

• A. Motility on gels
• B. Serological typing
• C. Gram staining
• D. Oxygen sensitivity

Answer: (B)

Serological typing uses antibodies to detect specific surface antigens on bacteria, so it can distinguish organisms based on their unique antigenic makeup. For Salmonella and Shigella, serotyping relies on surface components like O (somatic) and H (flagellar) antigens, organized in schemes that classify many serotypes. For Streptococcus, Lancefield grouping identifies bacteria by carbohydrate antigens present on the cell wall. Because these methods hinge on antigen–antibody interactions to reveal the identity of the organisms, serological typing is the appropriate approach. Motility tests measure movement, not antigens; Gram staining reveals Gram reaction and general morphology; oxygen sensitivity assesses growth under different oxygen levels—none of these identify organisms by surface antigens.

Serological typing uses antibodies to detect specific surface antigens on bacteria, so it can distinguish organisms based on their unique antigenic makeup. For Salmonella and Shigella, serotyping relies on surface components like O (somatic) and H (flagellar) antigens, organized in schemes that classify many serotypes. For Streptococcus, Lancefield grouping identifies bacteria by carbohydrate antigens present on the cell wall. Because these methods hinge on antigen–antibody interactions to reveal the identity of the organisms, serological typing is the appropriate approach.

Motility tests measure movement, not antigens; Gram staining reveals Gram reaction and general morphology; oxygen sensitivity assesses growth under different oxygen levels—none of these identify organisms by surface antigens.