The effect of a combination of ampicillin and sulbactam against clinical isolates of anaerobic bacteria

Abstract The antimicrobial susceptibility of 196 recent clinical isolates of anaerobic bacteria to ampicillin alone, ampicillin plus 1 μg/ml sulbactam, ampicillin plus 5 μg/ml sulbactam, and cefoxitin was studied by means of agar dilution tests. The ampicillin/sulbactam combination was most effective against species of the Bacteroides fragilis group, the minimum inhibitory concentration (MIC) 90 of ampicillin plus 5 μg/ml sulbactam for B. fragilis being 1 μg/ml, compared with 256 μg/ml of amoicillin, 4 μg/ml of ampicillin plus 1 μg/ml sulbactam, and 8 μg/ml of cefoxitin. No significant difference between ampicillin alone and in combination with sulbactam was observed against Gram-positive anaerobic rods or cocci.