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TITLE:  Characterization of Salmonella Typhimurium of animal origin obtained from the National Antimicrobial Resistance Monitoring System
AUTHORS:  Zhao S;Fedorka-Cray PJ;Friedman S;McDermott PF;Walker RD;Qaiyumi S;Foley SL;Hubert SK;Ayers S;English L;Dargatz DA;Salamone B;White DG;
YEAR:  2005
JOURNAL ABBREV:  Foodborne Pathog Dis
JOURNAL FULL:  Foodborne pathogens and disease
END PAGE:  181
KEYWORDS:  Ampicillin;Animals;Anti-Bacterial Agents;Bacteriophage Typing;Chloramphenicol;Denmark;drug effects;Drug Resistance,Bacterial;Drug Resistance,Multiple,Bacterial;drug therapy;Electrophoresis,Gel,Pulsed-Field;Food;Food Microbiology;Genetic Variation;genetics;Humans;Integrons;Microbial Sensitivity Tests;microbiology;Nalidixic Acid;pharmacology;Research;Salmonella;Salmonella Infections;Salmonella Infections,Animal;Salmonella typhimurium;Streptomycin;Tetracycline;Turkeys;United States;veterinary;Veterinary Medicine;
ABSTRACT:  Salmonella Typhimurium remains one of the most common causes of salmonellosis in animals and humans in the United States. The emergence of multi-drug resistant Salmonella reduces the therapeutic options in cases of invasive infections, and has been shown to be associated with an increased burden of illness. In this study, 588 S. Typhimurium (including var. Copenhagen) isolates obtained from either animal diagnostic specimens (n = 199) or food animals after slaughter/processing (n = 389) were examined for antimicrobial susceptibility, presence of class-1 integrons, and characterized using pulsed-field gel electrophoresis and phage typing. Seventy-six percent (448/588) of isolates were resistant to at least one antimicrobial. Salmonella isolates displayed resistance most often to streptomycin (63%), tetracycline (61%), ampicillin (61%), and to a lesser extent, chloramphenicol (36%), ceftiofur (15%), gentamicin (9%), and nalidixic acid (4%), with more resistance observed among diagnostic isolates. Salmonella recovered from turkeys (n = 38) exhibited the highest rates of resistance, with 92% of isolates resistant to least one antimicrobial, and 58% resistant to > or =10 antimicrobials. Class 1 integrons were present in 51% of all isolates. Five integron associated resistance genes (aadA, aadB, pse-1, oxa-2 and dhfr) were identified. A total of 311 PFGE patterns were generated using XbaI, indicating a genetically diverse population. The largest PFGE cluster contained 146 isolates, including DT104 isolates obtained from all seven animal species. Results demonstrated a varied spectrum of antimicrobial resistance, including several multidrug resistant clonal groups, among S. Typhimurium and S. Typhimurium var. Copenhagen isolates recovered from both diagnostic and slaughter/processing samples
AFFILIATIONS:  Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food & Drug Administration, 8401 Muirkirk Road, Laurel, MD 20708, USA. szhao@cvm.fda.gov