COMPARATIVE VIRULENCE OF BLOOD AND STOOL ISOLATES OF SHIGELLA-SONNEI

Shigellemia is rare in developed countries and might result from the e mergence of unusually virulent strains. We compared systemic invasiven ess markers of isolates from the blood of 3 temporally clustered patie nts with Shigella sonnei bacteremia in Boston with those of 11 unrelat ed contemporaneous strains from stools of people in New England. We fo und no difference between the two groups in O-chain length by sodium d odecyl sulfate-polyacrylamide gel electrophoresis, mouse 50% lethal do se, in vivo response to iron, and susceptibility to serum, which varie d from moderately susceptible to ultrasusceptible. Mean intraperitonea l 50% lethal doses of smooth form I colonies for mice were equally low (10(5.8) CFU) in both groups, and the 50% lethal doses were lowered e qually further in the two groups by predosing with iron to levels usef ul in mouse model sepsis studies. S. sonnei bacteremia may reflect com promised host defenses, not bacterial virulence.