A New Evolutionary Variant of the Streptogramin A Resistance Protein, Vga(A) LC , from Staphylococcus haemolyticus with Shifted Substrate Specificity towards Lincosamides

Abstract

ABSTRACT We found a new variant of the streptogramin A resistance gene, vga (A) LC , in clinical isolates of Staphylococcus haemolyticus resistant to lincomycin and clindamycin but susceptible to erythromycin and in which no relevant lincosamide resistance gene was detected. The gene vga (A) LC , differing from the gene vga (A) at the protein level by seven amino acid substitutions, was present exclusively in S. haemolyticus strains resistant to both lincosamides and streptogramin A (LS A phenotype). Antibiotic resistance profiles of the ATP-binding cassette (ABC) proteins Vga(A) LC and Vga(A) in the antibiotic-susceptible host S. aureus RN4220 were compared. It was shown that Vga(A) LC conferred resistance to both lincosamides and streptogramin A, while Vga(A) conferred significant resistance to streptogramin A only. Detailed analysis of the seven amino acid substitutions, distinguishing the two related ABC proteins with different substrate specificities, identified the substrate-recognizing site: four clustered substitutions (L212S, G219V, A220T, and G226S) in the spacer between the two ATP-binding cassettes altered the substrate specificity and constituted the lincosamide-streptogramin A resistance phenotype. A transport experiment with radiolabeled lincomycin demonstrated that the mechanism of lincosamide resistance in S. haemolyticus was identical to that of the reported macrolide-streptogramin B resistance conferred by Msr(A).