Molecular epidemiology of Salmonella Heidelberg in an equine hospital

From 1992 to 1997, multi-drug resistant (MDR) Salmonella Heidelberg isolate s were cultured from a number of horses hospitalised in a veterinary hospit al in Victoria, Australia, To examine the relationships between the cases, 28 isolates from the hospital were compared by pulsed field gel electrophor esis (PFGE), IS200 element profiles, antimicrobial resistance patterns, pla smid profiles and phage typing. The PFGE patterns following digestion with XbaI and BlnI restriction endonucleases showed that the isolates from the v eterinary hospital originated from a common source. These isolates also had indistinguishable IS200 profiles. However, PFGE was more discriminatory th an IS200 profiles. All the veterinary hospital isolates and one independent isolate had the same antimicrobial resistance pattern and had at least one plasmid in common. Localisation of antimicrobial resistance genes indicate d that the veterinary hospital isolates had more than one plasmid carrying resistance genes and that the genes encoding sulphathiazole and trimethopri m resistance were not on these plasmids. Phage typing was ineffective as 22 of the 28 isolates were untypeable. In conclusion, the combination of diff erent methods used for epidemiological studies suggested that a single stra in of MDR S. Heidelberg was isolated from horses admitted to the hospital f or 6 years and caused salmonellosis in susceptible horses within that perio d with no apparent correlation between the antimicrobials used and retentio n of its MDR phenotype, (C) 2001 Elsevier Science B.V. All rights reserved.