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U.S. Department of Health and Human Services

Animal & Veterinary

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FDA Veterinarian Newsletter November/December 1999 Volume XIV, No VI

The National Antimicrobial Resistance Monitoring System (NARMS) was the source of data for several posters at the American Society for Microbiology’s (ASM) annual meeting on infectious diseases. The 39th Interscience Conference on Antimicrobial Agents and Chemotherapy took place in San Francisco September 26-29. Dr. Linda Tollefson, Director of the Office of Surveillance and Compliance; Dr. Katherine Hollinger, an epidemiologist; Dr. Roger Jones, a toxicologist; and Dr. Linda Silvers, a veterinary medical officer, participated from CVM.

NARMS is a system developed by CVM that monitors bacterial isolates from humans who have become ill from enteric pathogens, and from food animals. Data are submitted by the Centers for Disease Control and Prevention and the U.S. Department of Agriculture under the program. Through this monitoring, public health officials can identify changes in bacteria that can indicate a change in resistance.

"Antibiotic resistance in Salmonella enterica serotypes heidelberg, kentucky, and thompson isolated from human and broiler chicken sources" was the subject of a poster by FDA/CVM, CDC/NCID and USDA/ARS. Human Salmonella serotypes were separated into two groups, those most frequently isolated from broilers and all others. Comparison between the two human groups showed differences in the prevalence of resistance for chloramphenicol, gentamicin, kanamycin and streptomycin. The largest difference among the human groups was observed for gentamicin where 13.0% of the broiler-associated group and 1.8% of the non-broiler-associated group were resistant (p<.001). Thus, the greater proportion of gentamicin resistance in persons ill with salmonellosis and submitting isolates to NARMS occurred in serotypes that were the most common serotypes isolated from broilers.

"Aminoglycoside resistance in Salmonella serotype typhimurium (STm) in the United States and Denmark: an association between resistance and aminoglycoside use in food animals" was a joint poster presentation between FDA/CVM, CDC/NCID, and DANMAP, a susceptibility monitoring program managed by the Danish Veterinary Laboratory and the Danish human diagnostic laboratory. Aminoglycoside resistance was found to be less prevalent among STm in Denmark than in the U.S. In both countries, the prevalence of aminoglycoside resistance corresponded to the availability of this class of antimicrobial agents for food animals.

"Isolation of quinupristin-dalfopristin (Synercid) resistant Enterococcus faecium from human stool specimens and retail chicken products in the United States" was the title of a poster by investigators from CDC/NCID, University of Maryland at Baltimore, and the Oregon and Georgia Health Departments. Synercid is a newly developed streptogramin antimicrobial agent for the treatment of vancomycin-resistant E. faecium infections in humans. A related streptogramin, virginiamycin, is used as a growth promoter in food animals. The investigators isolated quinupristin-dalfopristin resistant E. faecium from human stools and a high proportion of chickens from grocery stores in the U.S. Enterococci were isolated from 132 (88%) chickens. Isolates from 64 were further tested; 36 (56%) were E. faecium and 35 (97%) of these were quinupristin-dalfopristin resistant.

CDC/NCID, several state health departments, and DANMAP investigators presented "Presence of high-level gentamicin-resistant enterococci in humans and retail chicken products in the U.S. but not Denmark". High-level gentamicin resistance enterococci were isolated from 44% of chickens tested in the U.S. but none in Denmark. This high prevalence in the U.S. may be associated with the use of gentamicin in the U.S. chicken industry. High-level gentamicin resistant enterococci were also more common in human stools in the U.S. than in Denmark, possibly due to ingestion of chicken containing gentamicin-resistant enterococci.