N-formimidoyl-thienamycin activity against anaerobes: effect of the inoculum, pH and culture media

Abstract
The effect of three different culture media, three medium pH values and three inoculum densities on in-vitro activity of thienamycin against 100 isolates of anaerobes was tested. All media gave similar results for 50 Bacteroides spp. (25 β-lactamase producers), 25 clostridia and 14 Peptococcus spp. MICs for 12 Peptostreptococcus spp. were three times higher in brain-heart agar than in Brucella or Wilkins-Chalgren Agar. Medium pH 6–8, and inoculum density between 103–107 did not affect MIC significantly. All Bacteroides strains were inhibited at 0·125 mg/l and β-lactamase production had no effect. All Clostridia strains and Peptococcus spp. were inhibited at 0·125 mg/l, while the Peptostreptococcus spp. needed 1 mg/l.

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