Susceptibility of Brazilian staphylococcal strains to glycopeptides evaluated by different testing methods

Abstract

Reports of staphylococci with reduced susceptibility to glycopeptides are cause for concern. This study evaluated the susceptibility of 84 staphylococci clinical isolates to glycopeptides by the disk diffusion, agar dilution, E-test, and BHIA screening methods. Vancomycin agar dilution showed all strains presented minimum inhibitory concentration (MIC) ranging from 0.5 to 2 microg/ml, and the E-test showed similar results. Teicoplanin agar dilution test showed MICs ranging from < or = 0.5 to 2 microg/ml for Staphylococcus aureus and MICs ranging from <0.25 to 32 microg/ml for coagulase-negative Staphylococcus (CNS). Ten CNS isolates presented MICs ranging from 8 to 32 microg/ml for agar dilution and/or E-test. All the staphylococci were susceptible to vancomycin by the disk diffusion test (DDT), but two CNS isolates presented intermediate resistance to teicoplanin by the DDT and MICs of susceptibility, with two other CNS strains, teicoplanin-susceptible by the DDT, presented MICs of intermediate resistance. On the vancomycin-containing agar, 20 CNS isolates were able to grow, but no S. aureus strain. All these isolates showed MICs to teicoplanin (4-32 microg/ml) higher than those isolates that did not grow on the agar screen plate. PFGE of chromosomal SmaI digests showed a wide diversity of these CNS strains, without any predominance of a single PFGE pattern.