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Applied and Environmental Microbiology, December 2006, p. 7575-7585, Vol. 72, No. 12
0099-2240/06/$08.00+0 doi:10.1128/AEM.01174-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Multilocus Sequence Typing Supports the Hypothesis that Cow- and Human-Associated Salmonella Isolates Represent Distinct and Overlapping Populations
,
S. D. Alcaine,1
Y. Soyer,1
L. D. Warnick,2
W.-L. Su,1
S. Sukhnanand,1
J. Richards,1
E. D. Fortes,1
P. McDonough,2
T. P. Root,3
N. B. Dumas,3
Y. Gröhn,2 and
M. Wiedmann1*
Department of Food Science,1 Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, New York 14853,2 Wadsworth Center, New York State Department of Health, Albany, New York3
Received 21 May 2006/ Accepted 25 September 2006
A collection of 179 human and 156 bovine clinical Salmonella isolates obtained from across New York state over the course of 1 year was characterized using serotyping and a multilocus sequence typing (MLST) scheme based on the sequencing of three genes (fimA, manB, and mdh). The 335 isolates were differentiated into 52 serotypes and 72 sequence types (STs). Analyses of bovine isolates collected on different farms over time indicated that specific subtypes can persist over time on a given farm; in particular, a number of farms showed evidence for the persistence of a specific Salmonella enterica serotype Newport sequence type. Serotypes and STs were not randomly distributed among human and bovine isolates, and selected serotypes and STs were associated exclusively with either human or bovine sources. A number of common STs were geographically widespread. For example, ST6, which includes isolates representing serotype Typhimurium as well as the emerging serotype 4,5,12:i:-, was found among human and bovine isolates in a number of counties in New York state. Phylogenetic analyses supported the possibility that serotype 4,5,12:i:- is closely related to Salmonella serotype Typhimurium. Salmonella serotype Newport was found to represent two distinct evolutionary lineages that differ in their frequencies among human and bovine isolates. A number of Salmonella isolates carried two copies of manB (33 isolates) or showed small deletion events in fimA (nine isolates); these duplication and deletion events may provide mechanisms for the rapid diversification of Salmonella surface molecules. We conclude that the combined use of an economical three-gene MLST scheme and serotyping can provide considerable new insights into the evolution and transmission of Salmonella.
* Corresponding author. Mailing address: Department of Food Science, 412 Stocking Hall, Cornell University, Ithaca, NY 14853. Phone: (607) 254-2838. Fax: (607) 254-4868. E-mail: mw16{at}cornell.edu.
Published ahead of print on 6 October 2006.
Supplemental material for this article may be found at http://aem.asm.org/.
Applied and Environmental Microbiology, December 2006, p. 7575-7585, Vol. 72, No. 12
0099-2240/06/$08.00+0 doi:10.1128/AEM.01174-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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