Resistance of Vibrio vulnificus to serum bactericidal and opsonizing factors: relation to virulence in suckling mice and humans.

Vibrio vulnificus causes soft-tissue infections, gastrointestinal disease, and severe sepsis in humans. Bacterial and host factors in virulence have remained poorly defined. We found that blood culture isolates of V. vulnificus were completely resistant to the bactericidal effects of 10% normal human serum, in contrast to soft-tissue and environmental isolates that showed a mean 2.6 log10 decline during 120 min of incubation. Following opsonization by 10% normal human serum, mean uptake of blood isolates by normal human polymorphonuclear leukocytes during 20 min of incubation in vitro was 45.8% compared with 83.2% for isolates from other sites. Blood isolates were lethal for suckling mice (mean LD50, 1.3 X 10(6)) in contrast with isolates from other sites, which were less virulent (mean LD50, 1 X 10(9)); lethality correlated well with bacteremia at 6 hr. These studies show a close correlation between bacterial virulence for humans and suckling mice and suggest that resistance to the bactericidal and opsonizing effects of normal human serum may be important factors governing that virulence.