Utilization of both phenotypic and molecular analyses to investigate an outbreak of multidrug-resistant Salmonella anatum in horses.
Phenotypic and molecular techniques, including antimicrobial susceptibility testing, plasmid analysis, and pulsed-field gel electrophoresis (PFGE) were used to characterize 15 isolates of multidrug-resistant (MDR) Salmonella anatum cultured during a 16 mo period from horses and a veterinary clinic environment. The isolates were resistant to multiple antimicrobial agents and could be placed into 4 groups based on their antimicrobial resistance patterns. The isolates contained multiple plasmids ranging in size from 2 to > 100 kb that could be grouped into 3 different plasmid profile patterns; these patterns did not correlate with the antimicrobial resistance groupings. Furthermore, antimicrobial resistance was conjugatively transferable. Digestion of genomic DNA from the 15 isolates with 3 different restriction endonucleases, SfiI, SpeI, and XbaI followed by PFGE revealed a highly conserved restriction endonuclease digestion pattern. In contrast, diverse banding patterns were observed with S. anatum obtained from other sources. These observations suggest that the MDR S. anatum isolates represent a common outbreak strain even though they possess different, albeit similar, antibiograms and plasmid profiles. The study showed that PFGE is a useful epidemiological tool for discriminating between unrelated and outbreak-related strains of S. anatum. In conclusion, epidemiological studies of outbreaks caused by MDR isolates of S. anatum should consist of both genotypic and phenotypic methods of analysis.
Hartmann
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Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison 53706, USA.
West
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D000818:Animals; D004262:DNA Restriction Enzymes; D004269:DNA, Bacterial / Q000032:analysis* / Q000235:genetics; D004196:Disease Outbreaks / Q000662:veterinary*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field / Q000379:methods / Q000662:veterinary; D005838:Genotype; D006734:Horse Diseases / Q000175:diagnosis / Q000453:epidemiology* / Q000382:microbiology; D006736:Horses; D010641:Phenotype; D010957:Plasmids; D012475:Salmonella / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D012481:Salmonella Infections, Animal / Q000175:diagnosis / Q000453:epidemiology* / Q000382:microbiology
D004269:DNA, Bacterial; D004262:DNA Restriction Enzymes