The in-vitro activity of metronidazole against Enterobacteriaceae alone and in mixed cultures with Bacteroides fragilis.

The in-vitro antimicrobial action of therapeutic concentrations of metronidazole against Bacteroides fragilis and six different strains of Enterobacteriaceae in pure and mixed cultures have been studied. Under anaerobic conditions, metronidazole suppressed the growth of pure cultures of the Enterobacteriaceae. A reduction in the viable counts from 10(9) cfu/ml, in the 24 h controls, to 10(8), 10(7) and 10(5) cfu/ml in the presence of 10, 50 and 100 mg/l of metronidazole respectively, was observed. These concentrations of drug produced a marked bactericidal effect against B. fragilis, as expected. The antimicrobial activity of metronidazole on mixed cultures of B. fragilis and each one of the Enterobacteriaceae studied was greater against both micro-organisms than the corresponding effect on their respective pure cultures, under the same experimental conditions.