Penicillin resistance and aminoglycoside-penicillin synergy in enterococci.
Susceptibility to penicillin, vancomycin, imipenem, streptomycin, kanamycin and gentamicin was tested in 130 clinical isolates of Enterococcus spp. by an agar dilution method. Penicillin resistance (MIC > 8 mg/l) was only observed among strains of Enterococcus faecium and Enterococcus raffinosus. Thirty-nine percent of the penicillin-resistant enterococci showed low-level resistance to at least one of the three aminoglycosides tested (gentamicin, kanamycin and streptomycin). Six Enterococcus strains (5 E. faecium and 1 E. raffinosus) with low-level resistance to gentamicin and different MICs for penicillin were tested for antibiotic synergy using time-killing curves. When penicillin concentrations equal to or higher than the MICs were used, synergism was established, even when highly penicillin-resistant strains (MIC > 200 mg/l) were tested. No synergy was observed when penicillin concentrations were below the MICs.
Lopardo
H A
HA
Laboratorio de Microbiología, Hospital de Pediatría, Prof. Dr. J.P. Garrahan, Buenos Aires, Argentina.
Venuta
M E
ME
Rubeglio
E A
EA
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004357:Drug Synergism; D016983:Enterococcus / Q000145:classification / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010403:Penicillin Resistance; D010406:Penicillins / Q000494:pharmacology*; D013045:Species Specificity; D014640:Vancomycin / Q000494:pharmacology
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D010406:Penicillins; D014640:Vancomycin