Prevalence of streptogramin resistance in enterococci from animals: Identification of vatD from animal sources in the United States

Authors: Jackson, Charlene; Cray, Paula; Barrett, John; Hiott, Lari; Woodley, Tiffanie

Submitted to: International Journal of Antimicrobial Agents
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2007
Publication Date: 7/1/2007
Citation: Jackson, C.R., Cray, P.J., Barrett, J.B., Hiott, L.M., Woodley, T.A. 2007. Prevalence of streptogramin resistance in enterococci from animals: Identification of vatD from animal sources in the United States. International Journal of Antimicrobial Agents. 30(1):60-66.

Interpretive Summary: Streptogramin antimicrobials (Quinupristin/Dalfopristin; Q/D) are used in human medicine to treat vancomycin-resistant Enterococcus faecium bacteremia. Previous reports suggest that streptogramin resistance among enterococci is common 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 was 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. A total of 6227 enterococci were collected and 1029/6227 (17%) Q/D resistant, non-E. faecalis enterococci were identified. Using PCR to detect genes responsible for macrolide and streptogramin resistance, 56% were positive for ermB, 3% for msrC, 2% for vatE, and 0.3% for vatD; 39% of the isolates were negative for all genes tested. These data indicate that Q/D resistance among enterococci from animals remains low even with the long use of virginiamycin and suggests that use in animal production does not contribute to the observed development of resistant bacteria recovered from humans. This information will be useful for policy makers and researchers when studying the effects of antimicrobials used in animals on resistance.

Technical Abstract: There is considerable debate over the use of virginiamycin in animals to the contribution of Quinupristin/Dalfopristin (Q/D) resistance in humans as both are of the streptogramin class of antimicrobials. In this study, the prevalence and mechanisms of streptogramin resistance in enterococci from animals and the environment was investigated. From 2000-2004, enterococci were isolated from poultry carcass rinsates, fruits, vegetables, retail meats, and environmental samples or from on-farm swine and cattle fecal samples. Enterococcus isolates were identified to species and then tested for antimicrobial susceptibility. Q/D resistant isolates (MIC >4) were subjected to PCR using primers to streptogramin resistance genes (ermB, msrC, vatD, and vatE). From the analysis, 1029/6227 (17%) Q/D resistant, non-E. faecalis enterococci were identified. The majority of Q/D resistant isolates were E. hirae (n=349; 34%), followed by E. casseliflavus (n=271; 26%) and E. faecium (n=259; 25%). Using PCR, 56% (n=571) were positive for ermB, 3% (n=34) for msrC, 2% (n=20) for vatE, and 0.3% (n=3) for vatD; 39% (n=401) of the isolates were negative for all four genes. The vatD positive samples were E. faecium (n=2) from chicken carcass rinsates, and one E. hirae from a swine fecal sample. The nucleotide sequence of vatD from the three isolates was 100% homologous to published vatD sequences. These data indicate that Q/D resistance among enterococci from animals remains low even with the long history of virginiamycin use. The low prevalence of vatD suggests that the gene has not been widely disseminated among isolates recovered from a number of animals and environmental sources. To date, this is the first report of vatD from enterococci from animals in the US.