The Bactericidal Action of Human Serum on Bacteroides Species

Abstract

SUMMARY. Sera obtained from 60 healthy normal subjects were tested for their inhibitory action against four clinical isolates of the Bacteroides fragilis group. All the sera inhibited clinical strains of B. vulgatus and B. ovatus, 92% of 60 sera inhibited B. thetaiotaomicron and 62% inhibited B. fragilis. Bacterial inhibition required components of uninactivated serum and was related to the serum concentrations and species of the bacteria. The viable counts of all the strains, except B. fragilis, were significantly reduced in pooled sera from patients with anaerobic systemic infections and from non-infected patients. The bactericidal activity of the sera from infected patients was more pronounced than that of the 'normal' sera, on all strains except B. fragilis. These observations may explain in part the predominance of B. fragilis in serious clinical infections involving anaerobes.

Virulence markers and antimicrobial susceptibility of bacteria of the Bacteroides fragilis group isolated from stool of children with diarrhea in São Paulo, Brazil

“…The capsular polysaccharide B. fragilis acts as a protector against neutrophil phagocytes and the complement bactericidal activity; it can produce abscesses in animals (Lindberg & Weintraub 1985). Moreover, all the tested strains showed characteristics such as β-hemolytic, hydrophilic, and human or horse serum resistant, in accordance with Rotimi and Eke (1984), Oyston and Handley (1990), and Namavar et al (1991).…”

“…The serum bactericidal activity is perhaps the most important host's resistance factor against the systemic bacterial invasion. Thus, the resistance of the B. fragilis strain against human or horse sera may explain its pathogenic potential in severe clinical infections (Rotimi & Eke 1984). Namavar et al (1991) showed that avirulent B. fagilis strains were more sensitive to serum than the virulent ones, indicating that the complement is crucial for killing of avirulent strains.…”

Espécies do grupo Bacteroides fragilis em bezerros com e sem diarréia aguda: ocorrência, fatores de virulência e caracterização molecular

“…A resistência ao soro representa também alguma associação com a cápsula e/ou com a camada lipopolissacarídica, participando em conjunto da virulência desse grupo microbiano. É sabido que a atividade do soro constitui um importante fator de resistência do hospedeiro contra a invasão sistêmica pelos microrganismos EKE, 1984). Da mesma forma, a maioria dos isolados mostraram resistência à 60 o C por 30 minutos e em alguns casos, por mais de 60 minutos, o que sem dúvida também colabora com o potencial patogênico dessas bactérias (SHARP, 1999).…”