A new evolutionary variant of the streptogramin A resistance protein, Vga(A)LC, from Staphylococcus haemolyticus with shifted substrate specificity towards lincosamides

Antimicrob Agents Chemother. 2006 Dec;50(12):4070-6. doi: 10.1128/AAC.00799-06. Epub 2006 Oct 2.

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).

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Bacterial Proteins / physiology*
  • Base Sequence
  • DNA, Bacterial / genetics
  • DNA, Bacterial / isolation & purification
  • Drug Resistance, Multiple, Bacterial
  • Evolution, Molecular*
  • Genes, Bacterial
  • Genetic Variation*
  • Humans
  • Lincosamides
  • Macrolides / pharmacology*
  • Microbial Sensitivity Tests
  • Sequence Analysis, DNA
  • Staphylococcus aureus / drug effects
  • Staphylococcus aureus / genetics
  • Staphylococcus haemolyticus / drug effects*
  • Staphylococcus haemolyticus / genetics
  • Staphylococcus haemolyticus / isolation & purification
  • Streptogramin A / pharmacology*
  • Substrate Specificity

Substances

  • Bacterial Proteins
  • DNA, Bacterial
  • Lincosamides
  • Macrolides
  • Streptogramin A