In Vitro Activity of Cefpirome against Streptococcus pneumoniae Strains with Decreased Susceptibility to Cefotaxime

Abstract

During 1995, the French National Reference Centre for Pneumococci received 4965 strains of S. pneumoniae. CTX MICs (mg/mL) against these strains were: #0.25 mg/mL, n 5 3049; 0.5 mg/mL, n 5 497; 1 mg/mL, n 5 1378; $2 mg/mL, n 5 41. One hundred twenty strains were included in this study: 41 strains with CTX MICs .1 mg/mL (CTX-resistant strains, according to National Committee for Clinical Laboratory Standards breakpoint); 53 strains and 26 strains with CTX MICs equal to 1 and 0.5 mg/L, or intermediately resistant and susceptible, respectively. MICs were determined by agar dilution method in Mueller-Hinton medium supplemented with 5% horse blood. The antimicrobials were supplied as powders of known potency by the manufacturers. Strains were inoculated in brain-heart infusion broth supplemented with 10% ascitic fluid and shaken for 3 h in a water bath at 37°C. An inoculum of 10–10 CFU per spot was applied to the surface of Mueller-Hinton agar plates containing serial twofold dilutions of each drug with a Steers multipoint inoculator. The plates were incubated in 5% CO2-air at 37°C for 18 h, and the MIC was defined as the lowest concentration of antibiotic that completely prevented visible growth of the inoculum. Staphylococcus aureus ATCC 25923 was used as a control strain.