EPIDEMIOLOGY, ECOLOGY, AND MOLECULAR GENETICS OF ANTIMICROBIAL RESISTANCE IN PATHOGENIC AND COMMENSAL BACTERIA FROM FOOD ANIMALS
Location: Bacterial Epidemiology and Antimicrobial Resistance
Title: First report of vatB and vgaB from Enterococcus gallinarum in the USA
Submitted to: International Journal of Antimicrobial Agents
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2007
Publication Date: February 1, 2008
Citation: Jackson, C.R., Cray, P.J., Barrett, J.B., Hiott, L.M., Woodley, T.A. 2008. First report of vatB and vgaB from Enterococcus gallinarum in the USA.International Journal of Antimicrobial Agents. 31(2):175-187.
Interpretive Summary: The streptogramin antimicrobial Quinupristin/Dalfopristin (Q/D) is only used in human medicine to treat vancomycin-resistant Enterococcus faecium bacteremia. Conversely, virginiamycin is a streptogramin antimicrobial which is used in veterinary medicine only. Previous reports suggest that streptogramin resistance among enterococci is common in both humans and animals and streptogramin resistance can be attributed to the use of virginiamycin in animals. In this study, prevalence and mechanisms of streptogramin resistance in enterococci from animals and the environment were investigated. From 2000-2004, enterococci were isolated from poultry carcass rinsates, fruits, vegetables, retail meats, and environmental rinsates or from swine and cattle fecal samples collected on-farm. Enterococcus isolates were identified to species and then analyzed for antimicrobial susceptibility. One strain, Enterococcus gallinarum ARS 9402, isolated from chickens, was resistant to bacitracin, flavomycin, lincomycin, Q/D, tetracycline, and tylosin. Using PCR specific for streptogramin resistance genes, the isolate was positive for vatB and vgaB which were previously only identified in Staphylococcus aureus. Other tests of analysis suggests that the genes may be linked. This information will be useful for policy makers and researchers when studying the effects of antimicrobials used in animals on resistance.
There is much debate surrounding the contribution agricultural use of antimicrobials has on human health. One debate concerns the use of virginiamycin in animals and Quinupristin/Dalfopristin (Q/D) resistance in humans. In a study of prevalence of streptogramin resistance in enterococci, an Enterococcus gallinarum strain was isolated from chickens and was resistant to bacitracin (>128 ug/ml), flavomycin (>32 ug/ml), lincomycin (>32 ug/ml), Q/D (8 ug/ml), tetracycline (>32 ug/ml), and tylosin (>32 ug/ml). Using PCR to streptogramin resistance genes, the isolate was positive for vatB and vgaB, previously only identified in Staphylococcus aureus. The E. gallinarum vatB sequence differed from S. aureus vatB by one nucleotide at base 420 (A420 to T), but did not result in an amino acid change. For vgaB, three nucleotide differences 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, vatB and vgaB probes hybridized to identical SmaI fragments between 54.7-78.2-kb suggesting that the genes may be linked. To our knowledge, this is the first report of vatB and vgaB identified in enterococci.