ARS | Publication request: Antimicrobial resistance of enterococci from animals

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: November 14, 2006
Publication Date: November 14, 2006
Citation: Jackson, C.R. 2006. Antimicrobial resistance of enterococci from animals. Florida A&M University. November 14, 2006. Tallahassee, Fl.

Technical Abstract: There is increasing concern over antimicrobial resistance in bacteria of animal and human origin including the possibility of transfer of resistance genes between animal to human bacteria, particularly, those that may be pathogenic. The reported increases in resistance are thought to result from antimicrobial use in animals and use of antimicrobials for growth promotion in animals is considered to impact human health. Subsequent development of cross-resistance to therapeutic antimicrobial agents used in treatment of human infections is thought to occur when commensal bacteria transfer their resistance genes. An example of cross-resistance and treatment concerns is evident in vancomycin-resistance and streptogramin-resistance in enterococci. Recently, Synercid [Quinupristin-Dalfopristin (Q/D)], a combination streptogramin A and B antimicrobial, was approved for the treatment of vancomycin resistant Enterococcus faecium (VREF). Virginiamycin, an analog of Synercid, has been used in animal production for over two decades, it is possible that Q/D resistant E. faecium have already emerged in the animal population which could be disseminated among humans and impact treatment. 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% homogolous to published vatD sequences. These data indicate that Q/D resistance among enterococci from animals remain 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 U.S.