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Infection and Immunity, November 1999, p. 5651-5657, Vol. 67, No. 11
Program in Infectious Diseases and Immunity,
School of Public Health, University of California at Berkeley,
Berkeley, California,1 and Department of
Medicine, Division of Infectious Diseases, University of Colorado
Health Sciences Center, Denver, Colorado2
Received 17 May 1999/Returned for modification 5 August
1999/Accepted 9 August 1999
Salmonella enterica serotype Enteritidis (S. enteritidis) is a major food-borne pathogen, and its incidence
among all Salmonella serotypes has increased dramatically
in the last two decades. To study the virulence characteristics of
clinical isolates of S. enteritidis, we determined the 50%
lethal doses (LD50) in mice of isolates of two major phage
types (4 and 8). Isolates of both phage types showed a wide range of
LD50 after oral inoculation, varying from under
102 organisms to over 108 organisms. No
significant difference in LD50 was observed between the
phage types. These observations indicated that clinical isolates of
S. enteritidis are highly heterogeneous in their ability to cause death in mice. We compared the LD50s of these
isolates to the results observed from in vitro pathogenicity assays. We
also analyzed these isolates for recognized Salmonella
virulence loci (spv, sodCI, sopE,
and sef). The in vitro phenotypes of the isolates showed no
obvious correlation with their LD50 in any given assay, and
the virulence genes tested were present in all isolates. However, the
isolate with the lowest LD50 (isolate 97A 2472) was
resistant to acidified sodium nitrite (ASN). Moreover, the most
acid-susceptible, macrophage-susceptible, and ASN-susceptible isolates
were attenuated for virulence in mice. These results, based on
extensive analysis of clinical isolates of S. enteritidis,
demonstrate the complex nature of Salmonella pathogenesis
in mice. Our results also indicate the limitation of in vitro assays in
predicting in vivo virulence.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Analysis of Virulence of Clinical Isolates of
Salmonella enteritidis In Vivo and In Vitro
*
Corresponding author. Mailing address: 140 Warren Hall,
School of Public Health, University of California at Berkeley,
Berkeley, CA 94720. Phone: (510) 642-9200. Fax: (510) 642-6350. E-mail: lwriley{at}uclink4.berkeley.edu.
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