Survey of Antimicrobial Resistant Enterococci in Animals

Over the last 10 years much has been learned about the epidemiology of antibiotic resistance in human isolates of enterococci. One of the most formidable treatment problems that has emerged over the last few years has been vancomycin-resistant Enterococcus faecium (VREF). Most of these isolates are resistant to multiple antibiotic agents. In Michigan hospitals VREF has emerged as a significant problem. Data from the Michigan Department of Public Health (MDPH) Sentinel Surveillance Hospital System indicated resistance rates of 45% to vancomycin in E. faecium in the fourth quarter of 1997. The epidemiology for dissemination of resistance genes in enterococcus is complex. Little is known about reservoirs for resistant strains and risk factors outside of the hospital setting. The incidence of resistant enterococci in food animals and the role of these animals as a source of resistant strains or 'new' resistance genes that can be acquired by humans is not defined.
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The overall purpose of this research project is to gain a better understanding of the prevalence and spread of antibiotic resistant enterococci in food animals. These studies will lead to better prevention and control methods. Our specific aims are as follows: <Ol> <LI> To establish information on state-wide (Michigan) prevalence rates for antibiotic resistant enterococci in food animals to evaluate their potential roles as reservoirs for drug resistant bacteria that could affect humans. This aim will be accomplished by collecting surveillance cultures from animals on farms throughout Michigan including poultry flocks, beef and dairy cattle and pig herds, to identify resistant enterococci; <LI> To characterize the molecular epidemiology of the resistant enterococci identified to better understand the genetic mechanism by which antibiotic resistance is spread between enterococcal strains. This aim will be accomplished by, a) evaluating relatedness of strains by pulse field gel electrophoresis (PFGE), b) conducting hybridization studies and PCR studies to evaluate isolates for the presence, prevalence, and location of known resistance genes and to identify and characterize new genes, and c) comparing resistance genes of E. faecium animal isolates with already characterized human isolates from the same geographic areas in Michigan; <LI> To collect information on risk factors for the development of antibiotic resistant enterococci in animals including source of isolates, antibiotic use and geographic and temporal clustering. </ol> Three years will be required to complete the work proposed in this application. A better understanding of risk factors and molecular epidemiology for dissemination of antibiotic resistance in enterococcus from food animals is essential in the design of control and prevention strategies for human acquisition.