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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.

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Financiamiento: Este estudio no tuvo financiamiento. Los autores no poseen conflictos de interés.

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We evaluated an agar disc diffusion test for the detection of high-level (> or = 2000 mg/L) and moderately high-level resistance to gentamicin (MIC, > or = 128- < or = 1024 mg/L) and streptomycin (MIC, > or = 256- < or = 1024 micrograms/ml) with 70 clinical isolates of Enterococcus faecium. Results obtained using disks containing 120 micrograms gentamicin and 300 micrograms streptomycin were compared with MICs determined by an agar dilution method. Based on the scattergrams, the closest zone diameter correlations with MIC breakpoints were as follows: susceptible, > or = 16 mm; and resistant, < or = 10 mm, for both streptomycin and gentamicin. No major or very major errors were found with either aminoglycoside using these values. We conclude that agar disk diffusion test can be used to accurately detect high-level or moderately high-level gentamicin and streptomycin resistance in E. faecium.

Arch Argent Pediatr 2016;114(4):e237-e240 / e237Presentación de casos clínicos RESUMEN Staphylococcus aureus es uno de los principales agentes etiológicos de infecciones en niños provenientes de la comunidad y del ámbito hospitalario. La gravedad de estos cuadros se asocia a factores de virulencia, entre los que se encuentra la leucocidina de Panton-Valentine. Tanto Staphylococcus aureus resistente como sensible a la meticilina producen esta leucocidina, aunque con frecuencia variable. Presentamos a dos niños con infección grave por Staphylococcus aureus sensible a la meticilina productor de leucocidina de Panton-Valentine con complicaciones osteoarticulares y endovasculares. Es fundamental la sospecha diagnóstica, el tratamiento antibiótico adecuado y el manejo quirúrgico precoz para mejorar el abordaje de estas infecciones. Se debe mantener la vigilancia epidemiológica para detectar la frecuencia de las infecciones causadas por estas bacterias. Palabras clave: Staphylococcus aureus, leucocidina de PantonValentine, resistencia a la meticilina, enfermedad invasiva. ABSTRACTStaphylococcus aureus is a major etiologic agent of infections in children from the community and the hospital setting. The severity of these conditions is associated with virulence factors, including the Panton-Valentine leukocidin. Both methicillin resistant and sensitive Staphylococcus aureus produce this leukocidin although with varying frequency. We present two children with severe infection by sensitive Staphylococcus aureus producer of Panton-Valentine leukocidin with musculoskeletal and endovascular complications. It is essential the suspected diagnosis, appropriate antibiotic treatment and early surgical management to improve the approach of these infections. Infección grave por Staphylococcus aureus meticilino sensible productor de leucocidina de Panton-Valentine: reportes de dos casos Severe infection by methicillin sensitive Staphylococcus aureus producing Panton-Valentine leukocidin: reports of two casesEpidemiological surveillance should be mantained to detect the frequency of infections caused by these bacteria.