Salmonella spp.

MICROBIOLOGY

• Facultatively anaerobic, gram-negative bacillus
• Genus has 2 species, Salmonella eterica and Salmonella bongori; most of the clinically important sub-species are within Salmonella enterica.
• Non-typhoidal strains: Foodborne acquisition (95% cases: outbreaks linked to multiple vehicles including eggs, poultry, meats, dairy or vegetables) or acquisition as zoonotic pathogen (such as reptiles).
• Infection with "typhoidal strains" (S. typhi [typhoid fever; serogroup D] and S. paratyphi [paratyphoid fever]) implies contact with person who is infected or a chronic carrier, or with contaminated food or water.
  • Humans are the only reservoirs for typhoid strains.
• Non-typhoidal strains classified by agglutination reactions to O antigens identifying serogroups A-E; approximately 2,500 serovars/serotypes exist. Most common in US are S. Typhimurium, S. Enteriditis, S. Newport.
• S. enterica or S. choleraesuis sometimes used as single name for clinically familiar serovars (e.g., S. enterica Typhimurium).
• Serotyping usually only performed in reference/state labs
• Diagnosis is via culture (of blood, stool, etc)
• Typhoidal species more difficult to Cx. Increased yield when blood, bone marrow and intestinal secretions Cx’d before or soon after ABx initiated
  • Recovery of organism possible from almost any site, but most commonly stool followed by blood
  • Oxidase and lactose negative.
  • Grows easily under both anaerobic and aerobic conditions on standard media for stool. Fresh stool specimen preferred; rectal swabs inferior. Using a Salmonella-Shigella agar allows for identification of hydrogen sulfide, which is produced by most Salmonellae.