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Penicillin resistance and aminoglycoside-penicillin synergy in enterococci
H A Lopardo1, M E Venuta, E A Rubeglio
1Laboratorio de Microbiología, Hospital de Pediatría, Prof. Dr. J.P. Garrahan, Buenos Aires, Argentina.
Abstract:
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.
Insights
Penicillin resistance in Enterococcus spp. is linked to aminoglycoside resistance. Combining penicillin with aminoglycosides shows synergy against resistant strains when penicillin levels meet or exceed the minimum inhibitory concentration.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Enterococcus species are significant causes of nosocomial infections.
- Antimicrobial resistance in Enterococcus poses a therapeutic challenge.
- Understanding resistance mechanisms and synergistic treatment options is crucial.
Purpose of the Study:
- To assess antimicrobial susceptibility of clinical Enterococcus isolates.
- To investigate the relationship between penicillin and aminoglycoside resistance.
- To evaluate the synergistic potential of penicillin and aminoglycosides.
Main Methods:
- Agar dilution method for susceptibility testing of 130 clinical Enterococcus isolates.
- Testing against penicillin, vancomycin, imipenem, streptomycin, kanamycin, and gentamicin.
- Time-killing curves to assess antibiotic synergy in selected resistant strains.
Main Results:
- Penicillin resistance was observed in Enterococcus faecium and Enterococcus raffinosus.
- 39% of penicillin-resistant strains showed low-level resistance to gentamicin, kanamycin, or streptomycin.
- Synergistic activity of penicillin and aminoglycosides was demonstrated when penicillin concentrations were at or above the MIC.
Conclusions:
- Penicillin resistance in Enterococcus is associated with aminoglycoside resistance.
- Combination therapy with penicillin and aminoglycosides can be synergistic against resistant Enterococcus strains.
- Effective synergy requires penicillin concentrations to meet or exceed the minimum inhibitory concentration.