Clonal Diversity among Streptogramin A-Resistant Staphylococcus aureus Isolates Collected in French Hospitals

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Abstract
We analyzed 62 clinical isolates of streptogramin A-resistant (SGA r ) Staphylococcus aureus collected between 1981 and 2001 in 14 hospitals located in seven French cities. These isolates, including five with decreased susceptibility to glycopeptides, were distributed into 45 antibiotypes and 38 Sma I genotypes. Each of these genotypes included between 1 and 11 isolates, the Sma I patterns of which differed by no more than three bands. Although numerous clones were identified, we observed the spread of monoclonal isolates either within the same hospital or within hospitals in distinct cities and at large time intervals. Hybridization with probes directed against 10 SGA r genes ( vatA , vatB , vatC , vatD , vatE , vgaA , vgaB , vgaAv , vgbA , and vgbB ) revealed six patterns: vgaAv (21 isolates), vatA - vgbA (24 isolates), vgaAv - vatB - vgaB (14 isolates), vgaAv - vatA - vgbA (1 isolate), vgaAv - vatA - vgbA - vatB - vgaB (1 isolate), and vgaA (1 isolate). We detected at least one SGA r determinant in all of the tested isolates. vgaAv , which is part of the recently characterized transposon Tn 5406 , was found in 59.7% of the tested isolates. Of the 16 streptogramin B-susceptible isolates, 14 carried vgaAv alone and were susceptible to the mixtures of streptogramins, whereas the 2 isolates carrying vgaAv - vatB - vgaB were resistant to these mixtures. vatA - vgbA was found on plasmids of the same apparent size in 26 (42%) of the tested clinical isolates from 18 unrelated Sma I genotypes. The possible dissemination of some of the multiple clones characterized in the present study with an expected increased selective pressure of streptogramins following the recent licensing of Synercid (quinupristin-dalfopristin) must be carefully monitored.

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