Colonies are mucoid and lactose-fermenting, similar to Klebsiella colonies. It is mainly a nosocomial pathogen associated with UTIs, pneumonia, and sepsis following instrumentation.
Produces a non-diffusible red pigment in culture. It is a slow lactose fermenter. It is associated with hospital-acquired UTIs, pneumonia, sepsis, wound infections, and endocarditis in intravenous drug abusers.
A minor pathogen that can cause UTIs, meningitis, and otitis media. It may show false-positive tests for Salmonella due to antigen sharing.
It is the causative organism of dysentery (passage of blood and mucus in loose stools).
Some strains produce exotoxins. The most dangerous is verocytotoxin, which is the same as the EHEC verotoxin (as discussed above under EHEC). Even as few as 10 bacilli can cause infection.
Patients present with:
Fever may be present. Intestinal ulcers may develop. Secondary complications can occur, including arthritis, conjunctivitis, intussusception, parotitis, and HUS.
Stool samples show pus cells and RBCs. Culture on Mac Conkey’s agar shows non-lactose-fermenting colonies.
No H2S is produced, so there is no blackening of:
Biochemical tests help differentiate the strains. Mannitol is fermented by all strains except Shigella dysenteriae. Shigella sonnei ferments sucrose and lactose late.
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