Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/8/2006
Publication Date: 6/1/2007
Citation: Dunowska, M., Morley, P.S., Traub-Dargatz, J.L., David, M.A., Patterson, G., Frye, J.G., Hyatt, D.R., Dargatz, D.A. 2007. Comparison of salmonella enterica serotype infantis isolates from a veterinary teaching hospital. Journal of Applied Microbiology. 102(6):1527-1536. Interpretive Summary: Outbreaks of S. Infantis caused the closing of a veterinary hospital in 1996 and 2001. A study was done to compare 1996 outbreak isolates of S. Infantis and isolates from subsequent years to determine if these two outbreaks were caused by the same clone of S. Infantis. Fifty-six isolates were compared based on antimicrobial drug susceptibility pattern, pulsed field gel electrophoresis [PFGE] pattern and presence of integrons. There were 12 resistance profiles observed. A high percentage of isolates (80.3%) was resistant to at least 1 antimicrobial compound, with 67.8% showing resistance to > 5. All but one hospital isolate were closely related with more than 88% similarity by PFGE. Some isolates from various animal and environmental sources were indistinguishable by PFGE. The results of this study suggest that at least some of the infections were due to the spread of a clone and thus nosocomial in nature.
Technical Abstract: Objective: To compare Salmonella enterica serotype Infantis isolates obtained from patients or the environment of a veterinary teaching hospital over a period of 9 years. Design: Retrospective study. Sample Population: 56 S. Infantis isolates obtained from a veterinary teaching hospital from 1996 to 2004. Procedure: S. Infantis isolates were compared based on their phenotypic (antimicrobial drug susceptibility pattern) and genotypic (pulsed field gel electrophoresis [PFGE] pattern and presence of integrons) characteristics. Results: There were 12 resistance profiles observed among 56 isolates. On occasion, isolates indistinguishable by PFGE showed different susceptibility patterns. A high percentage of isolates (80.3 %) were resistant to at least 1 antimicrobial drug (AMD), with 67.8 % showing resistance to >5 AMD. All but one isolate were closely related with more than 88% similarity based on PFGE patterns. The majority (77.8 %) of isolates tested positive for type 1 integrons. Conclusion and Clinical Relevance: The results of this study cannot determine whether the 1996 outbreak was a result of spread of a single S. Infantis clone, or a result of multiple introductions of several different clones. However, our results strongly suggest that some of the infections were due to a clonal spread and likely nosocomial in nature.