The synergistic effect of cefotaxime and desacetylcefotaxime against clinical isolates of anaerobic bacteria.

The synergistic interaction of cefotaxime and desacetylcefotaxime against 187 clinically significant anaerobic organisms was investigated. Fusobacterium nucleatum, Actinomyces odontolyticus, propionibacteria, lactobacilli, peptostreptococci, Streptococcus intermedius and Veillonella were sensitive to cefotaxime. Both Eubacterium lentum and Streptococcus morbillorum were resistant. The susceptibility of the clostridia varied from 0.125 to greater than 256 mg/L; only 20% of species demonstrated synergy between cefotaxime and desacetylcefotaxime. The minimum inhibitory concentration (MIC) of cefotaxime against members of the genus Bacteroides ranged from 0.0625 to greater than 256 mg/L. The MIC50 of cefotaxime to Bacteroides fragilis and B. vulgatus was lowered from 6 and 4 mg/L, respectively, to 2 and 1 mg/L, respectively, when 4 mg/L desacetylcefotaxime was added to the medium. Full or partial synergy was demonstrated by 50.7% of the Bacteroides species tested. While cefotaxime and desacetylcefotaxime act synergistically against many members of the genus Bacteroides, the MIC of at least 10% of strains is not affected by this combination.