Title: Identification and Characterization of the Streptogramin Resistance Genes, vatB and vgaB, from Enterococcus gallinarum in the United States Authors
Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: February 16, 2007
Publication Date: May 23, 2007
Citation: Jackson, C.R., Cray, P.J., Barrett, J.B., Hiott, L.M., Woodley, T.A. 2007. Identification and Characterization of the Streptogramin Resistance Genes, vatB and vgaB, from Enterococcus gallinarum in the United States. American Society for Microbiology Conference. 167/A(A-064):15. Technical Abstract: Streptogramins are combination antimicrobials which are divided into two groups: streptogramin A and B. Virginiamycin and Quinupristin-Dalfopristin (Q/D), both combination streptogramins, are used in animals and humans, respectively. There is much debate over the use of virginiamycin in animals to the contribution of Q/D resistance in humans. In a previous study of prevalence and mechanisms of streptogramin resistance in enterococci from animals and the environment, 1029/6227 (17%) Q/D resistant, non-E. faecalis enterococci were identified. The majority of Q/D isolates were E. hirae (n=349), followed by E. casseliflavus (n=271) and E. faecium (n=259). One strain from the study, Enterococcus gallinarum ARS 9402 was isolated from a chicken carcass rinse sample in 2003 and was resistant to bacitracin (>128 'g/ml), flavomycin (>32 'g/ml), lincomycin (>32 'g/ml), Q/D (8 'g/ml), tetracycline (>32 'g/ml), and tylosin (>32 'g/ml). Using PCR to detect streptogramin resistance genes (ermB, msrC, vatA, vatB, vatC, vatD, vatE, vgaA, vgaB, vgbA, and vgbB), the isolate was positive for vatB and vgaB, previously only identified in Staphylococcus aureus. The vatB sequence from E. gallinarum differed from S. aureus vatB by only one nucleotide at base 420 (A420 to T), but did not result in an amino acid change. For vgaB, three nucleotide differences between the two vgaB sequences were identified: T919 to G, G1063 to T, and C1128 to T. Two of the nucleotide changes, T919 to G and G1063 to T, resulted in two amino acid changes, Trp307 to Gly and Val355 to Phe, respectively. Using PFGE and Southern analysis, the vatB and vgaB probes hybridized to the same plasmid bands ranging in size from 12 kb to >16 kb suggesting that the genes are located on the same plasmid. To our knowledge, this is the first report of the streptogramin A resistance genes, vatB and vgaB, identified in enterococci. In addition, although combinations of streptogramin B resistance genes have been previously reported in enterococci, this data also represents the first report of a combination of more than one streptogramin A resistance gene in enterococci.