Resumo

Six glycopeptide resistance phenotypes have been described. VanA (high-level-resistance to vancomycin and teicoplanin), VanB (variable resistance to vancomycin and susceptibility to teicoplanin), VanD (moderate resistance to vancomycin and teicoplanin) and VanC, VanE, VanG (low-level-resistance to vancomycin and susceptibility to teicoplanin). A study investigating the presence of vanA in Enterococcus isolates from surveillance cultures of rectal swab showed seven isolates displaying phenotypic characteristics incongruent with the vanA genotype by disc diffusion method. This study aimed to characterize those isolates in respect to the presence of other van genes and to determine the minimum inhibitory concentration (MIC) for different antimicrobials. Isolates identification and MIC determinations were performed by automated system (Phoenix-100, Biomerieux). The MICs for vancomycin and teicoplanin were determined by E-test and microdilution, respectively, according to CLSI (2010). Specific PCR for vanA, vanB, VanC and VanD were performed according the literature. The results showed 100% of resistance to ampicillin (MIC> 32¦Ìg/mL), penicillin (MIC> 16 ¦Ìg/mL), erythromycin (MIC> 4 ¦Ìg/mL), norfloxacin (MIC> 8¦Ìg/mL), gatifloxacin (MIC> 4¦Ìg/mL), moxifloxacin (MIC> 4 ¦Ìg/mL) and high-level streptomycin (MIC> 1000 ¦Ìg/mL). On the other hand, 100% of the isolates were susceptible to daptomycin (MIC¡Ü 1 ¦Ìg/mL) tetracycline (MIC¡Ü 2 ¦Ìg/mL), linezolid (MIC¡Ü 4 ¦Ìg/mL) and high-level gentamicin (MIC ¡Ü 500 ¦Ìg/mL). For glycopeptides, all the isolates showed high-level-resistance to vancomycin (MIC¡Ý 256¦Ìg/mL) and six isolates showed susceptibility to teicoplanin (MIC 8¦Ìg/mL), suggesting a VanD-like phenotype. One isolate displayed MIC value of 32 ¦Ìg/mL for teicoplanin and confirmed to belong to the VanA phenotype. PCR results only detected the vanA gene in all the isolates analysed. We can conclude the six isolates described here display an unexpected VanD-like phenotype associated to the vanA genotype, as already noted by other authors in Brazil and other countries. Since this discrepancy between phenotype and genotype may be resulted of mutations in regulatory genes or rearrangement of the vanA cluster, it seems that these events are being more frequent and worldwide disseminated. Further studies investigating the presence of gene mutations in the isolates will be carried out.