Characterization of the mechanisms of fluoroquinolone resistance in vancomycin-resistant enterococci of different origins.

The mutations in gyrA and parC genes were analyzed in 22 vancomycin-resistant enterococci of different origins and species, which had varying susceptibility to ciprofloxacin (minimum inhibitory concentration, MIC: 0.5- >256 mg/l). All vanA or vanb2-containing strains with ciprofloxacin MIC of >32 mg/l presented amino acid changes in GyrA protein (S83I, S83Y, S83R or S83I-E87G) with/without changes in ParC protein (S80I or S80R or S80l). Strains with lower ciprofloxacin MICs presented the GyrA and parC wild type. One vanA-containing Enterococcus durans strain with a ciprofloxacin MIC of 64 mg/l presented the S83I and S80I changes in GyrA and ParC proteins, respectively. Two vanB2 Enterococcus faecium strains were typed by multi-locus-sequencetyping and both were ascribed to the CC17 clonal complex with two sequence-types (ST78 and ST17-like). All seven vancomycin-resistant and ciprofloxacin-resistant E. faecium strains showed ampicillin resistance (MIC 32-256 mg/l), identifying the following amino acid changes in PBP5 protein: Q461K, V462K, H470Q, M485A, N496K, A499T, E525D, N546T, A558T, G582S, K632Q, P642L, E629V and P667S, together with a serine insertion at position 466´. The 12 Enterococcus gallinarum and Enterococcus casseliflavus isolates included in the study exhibited an MIC for ciprofloxacin in the range 0.5-16 mg/l and no amino acid changes were identified in GyrA or ParC proteins. Specific mutations in gyrA and parC genes are associated with fluoroquinolone resistance in E. faecium and E. durans of different origins. © E.S.I.F.T. srl - Firenze