Submitted to: Interscience Conference on Antimicrobial Agents & Chemotherapy Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/5/2004
Publication Date: 10/10/2004
Citation: Zhao, S., Cray, P.J., Friedman, S., Mcdermott, P.F., Qaiyumi, S., Foley, S.L., Hubert, S.K., Ayers, S., English, L., Dargatz, D. 2004. Characterization of salmonella typhimurium from diagnostic samples and food animal carcasses. Interscience Conference on Antimicrobial Agents & Chemotherapy Proceedings. Abstract. C2-1994. P. 131
Technical Abstract: Background: 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. Methods: 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. Results: 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 of turkey origin (n=38) exhibited the highest rates of resistance, with 92% of isolates resistant to least one antimicrobial, and 60% resistant to greater than or equal to 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. Conclusions: Results indicate that integron-mediated antibiotic resistance is common among S. Typhimurium isolates, and that multi-drug resistant clones are widespread among diagnostic and slaughter/processing samples.