Characterization of a Variant of vga (A) Conferring Resistance to Streptogramin A and Related Compounds

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Abstract
A variant of the vga(A) gene (1,575 bp), encoding an ATP-binding cassette protein conferring resistance to streptogramin A and related antibiotics, was cloned from the chromosome of aStaphylococcus aureus clinical isolate and sequenced. The sequence of the variant was similar to that of the vga(A) gene (83.2% identity). However, the G+C content of the variant (35.6%) was higher than that of vga(A) (29%) and there was no cross hybridization between vga(A) and the variant at high stringency (≥60°C), the highest temperature at which a signal was detected being 55°C. Unlike previous reports forvga(A) and vga(B), the variant ofvga(A) may be present in multiple copies in the genome. These copies are chromosomal in some isolates and both chromosomal and plasmid-borne in others. Nucleotide sequences hybridizing at 65°C with the vga(A) variant were found in all the staphylococcal strains harboring plasmids carrying bothvga(B) and vat(B), which also encode resistance to streptogramin A.