Influence of metronidazole, chloramphenicol, clindamycin and penicillin G on growth and neuraminidase activity of Bacteroides fragilis

The effects of subinhibitory concentrations of metronidazole, chloramphenicol, clindamycin and penicillin G on cell growth and neuraminidase activity of Bacteroides fragilis were tested in six strains from clinical specimens and two type collection strains. All showed significant inhibition of cell growth at one half the MIC after 24 h incubation. Metronidazole at one quarter the MIC was significantly inhibitory after 24 and 48 h incubation. The neuraminidase activity remained unaltered, in comparison with controls, when metronidazole and clindamycin were tested. Chloramphenicol reduced the enzyme activity at both one half and one quarter the MIC. On the other hand, penicillin G enhanced the neuraminidase activity, although the difference was not statistically significant. These in-vitro effects may simulate the behaviour of the bacteria in abscesses in vivo.