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Applied and Environmental Microbiology, March 2008, p. 1757-1766, Vol. 74, No. 6
0099-2240/08/$08.00+0     doi:10.1128/AEM.02740-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Human Salmonella Clinical Isolates Distinct from Those of Animal Origin

Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, California 93106,¹ Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah 84132,² Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, California 95616,³ Faculty of Veterinary Science, University of Sydney, Camden, New South Wales 2570, Australia⁴

Received 5 December 2007/ Accepted 19 January 2008

The global trend toward intensive livestock production has led to significant public health risks and industry-associated losses due to an increased incidence of disease and contamination of livestock-derived food products. A potential factor contributing to these health concerns is the prospect that selective pressure within a particular host may give rise to bacterial strain variants that exhibit enhanced fitness in the present host relative to that in the parental host from which the strain was derived. Here, we assessed 184 Salmonella enterica human and animal clinical isolates for their virulence capacities in mice and for the presence of the Salmonella virulence plasmid encoding the SpvB actin cytotoxin required for systemic survival and Pef fimbriae, implicated in adherence to the murine intestinal epithelium. All (21 of 21) serovar Typhimurium clinical isolates derived from animals were virulent in mice, whereas many (16 of 41) serovar Typhimurium isolates derived from human salmonellosis patients lacked this capacity. Additionally, many (10 of 29) serovar Typhimurium isolates derived from gastroenteritis patients did not possess the Salmonella virulence plasmid, in contrast to all animal and human bacteremia isolates tested. Lastly, among serovar Typhimurium isolates that harbored the Salmonella virulence plasmid, 6 of 31 derived from human salmonellosis patients were avirulent in mice, which is in contrast to the virulent phenotype exhibited by all the animal isolates examined. These studies suggest that Salmonella isolates derived from human salmonellosis patients are distinct from those of animal origin. The characterization of these bacterial strain variants may provide insight into their relative pathogenicities as well as into the development of treatment and prophylactic strategies for salmonellosis.

Published ahead of print on 1 February 2008.