Inhibition of phagocytosis of E. coli by B. fragilis group--an in vitro study.

Bacteriodes fragilis group can inhibit the phagocytosis and killing of co-existing aerobes. Forty six strains of B.fragilis group are tested for their ability to resist phagocytosis and inhibit the killing of indicator organism, E. coli by denoting the viable count. Among the species of B. fragilis group, the inhibitory index of the phagocytic system was the highest with B. fragilis followed by B. thetaiotamicron. None of the strains of B. fragilis group were phagocytosed or killed in this system. This property of resisting the phagocytosis and killing of E. coli by B. fragilis group might be the contributing factor towards their prevalence in mixed infections.

Enzyme linked immunosorbent assay & indirect fluorescence assay for rapid diagnosis of Bacteroides fragilis infections.

Antibodies for B. fragilis (NCTC 9343) were detected in sera of 121 patients and 37 controls using four methods viz., enzyme linked immunosorbent assay (ELISA), indirect fluorescence test (JFA), countercurrent immunoelectrophoresis (CIE) and indirect haemagglutination test (IHA). Of 121 patients, 57 were culture positive for B. fragilis, 38 positive for anaerobes other than B. fragilis and 26 were negative for anaerobes. In the B. fragilis culture positive group, antibodies to B. fragilis were positive in 82.5, 84.2, 85.90 and 91.2 per cent patients by CIE, ELISA, IHA and IFA respectively. In B. fragilis positive patients IFA was more sensitive than IHA, which for other groups IHA was found to be more sensitive than IFA. When all groups were taken together IHA was found more sensitive than IFA. ELISA and IFA tests are recommended for rapid serological diagnosis of B. fragilis infections, where facilities for these tests are not available, CIE and IHA could be done. Cross reactivity with other Gram negative anaerobic and aerobic bacteria should be kept in mind since seropositivity varied for B. fragilis (82-91%). In infections with microbes other than B. fragilis seropositivity varied between 23.7 to 63.2 per cent and in patients having cultures sterile or positive for other organisms seropositivity was 30.8 to 42.3 per cent. This nonspecificity could be due to other antigens that cross react between B. fragilis and other anaerobes and aerobes or the use of an antigen lacking high purity.

Detection of Bacteroides infection by counter immunoelectrophoresis test.

The counterimmunoelectrophoresis (CIE) test using sonicated antigens of Bacteroides fragilis NCTC 2553 and a B. asaccharolyticus strain, standardised in the laboratory yielded a negative result in the 50 normal sera tested, while it was positive in 24 of 34 (71%) patients with infection due to black pigmented bacteroides and in 10 of 15 (67%) with B. fragilis infection. The microagglutination test (MAT) done in parallel showed a positivity of only 44 and 40 per cent respectively. The CIE test done with B. asaccharolyticus antigen was negative in 87 per cent of patients with infection due to B. fragilis whereas MAT showed cross reactivity to a greater extent.

Factores de patogenia de Bacteroides fragilis / Factors of Bacteroides fragilis pathogenicity

El colon humano contiene una flora microbiana compleja y numerosa. Aunque existen por lo menos 400 especies distintas de bacterias, normalmente 70% de aislamientos corresponde sólo a cuatro géneros: dos anaerobios y dos aerobios uno de éstos es bacteroides, con 30% del total, y las especies más numerosas (10*9 -10*10 microrganismos/g de peso seco de heces) de éste son: B. vulgatus, B. distasonis, B. thetaiotaomicron y, en menor cantidad, B. ovatus y B. fragilis (0.5% del total). Es indudable que Bacteroides desempeña un papel importante en el ecosistema del colon. Asimismo algunas especies com B. fragilis y, en menor grado, otras del mismo género, como B. distasonis, B. thetaiotaomicron y B. ovatus pueden causar, en especial, septicemias y abscesos cerebrales, pulmonares o abdominales