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Infect Immun, May 1998, p. 2310-2318, Vol. 66, No. 5
Department of Microbiology and Immunology,
Uniformed Services University of the Health Sciences, Bethesda,
Maryland 20814-4799,1 and
Institute of
Human Virology, Baltimore, Maryland 212012
Received 13 November 1997/Returned for modification 15 December
1997/Accepted 5 February 1998
Salmonella enterica serovar Typhi (hereafter referred
to as S. typhi) is a host-restricted pathogen that adheres
to and invades the distal ileum and subsequently disseminates to cause
typhoid fever in humans. However, S. typhi appears to be
avirulent in small animals. In contrast, other pathogenic salmonellae,
such as S. enterica serovars Typhimurium and Dublin
(S. typhimurium and S. dublin, respectively),
typically cause localized gastroenteritis in humans but have been used
as models for typhoid fever because these organisms cause a disease in
susceptible rodents that resembles human typhoid. In vivo, S. typhi has been demonstrated to attach to and invade murine M
cells but is rapidly cleared from the Peyer's patches without
destruction of the M cells. In contrast, invasion of M cells by
S. typhimurium is accompanied by destruction of these M
cells and subsequently sloughing of the epithelium. These data have
furthered our view that the early steps in the pathogenesis of
typhoidal and nontyphoidal Salmonella serovars are
distinct. To extend this concept, we have utilized an in vitro model to evaluate three parameters of initial host-pathogen interactions: adherence of three Salmonella serovars to human and murine
small intestinal epithelial cell (IEC) lines, the capacity of these salmonellae to invade IECs, and the ability of the bacteria to induce
interleukin-6 (IL-6) in these cell lines as a measure of host cell
activation and the host acute-phase response. The results demonstrate
that S. typhi adheres to and invades human small IECs better than either S. typhimurium or S. dublin.
Interestingly, invA and invE null mutants of
S. typhi are able neither to adhere to nor to invade IECs,
unlike S. typhimurium invA and invE mutants, which adhere to but cannot invade IECs. S. typhi also
induces significantly greater quantities of IL-6 in human small IEC
lines than either of the other two Salmonella serovars.
These findings suggest that differential host cytokine responses to
bacterial pathogens may play an important role in the pathological
sequelae that follow infection. Importantly, S. typhimurium
did not induce IL-6 in murine IECs. Since S. typhimurium
infection in mice is often used as a model of typhoid fever, these
findings suggest that, at least in this case, the mouse model does not
reflect the human disease. Taken together, our studies indicate that
(i) marked differences occur in the initial steps of S. typhi, S. typhimurium, and S. dublin
pathogenesis, and (ii) conclusions about S. typhi
pathogenesis that have been drawn from the mouse model of typhoid fever
should be interpreted conservatively.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Differential Early Interactions between
Salmonella enterica Serovar Typhi and Two Other Pathogenic
Salmonella Serovars with Intestinal Epithelial
Cells
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Uniformed Services University of the
Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-5799. Phone: (301) 295-3413. Fax: (301) 295-1545. E-mail:
metcalf{at}usuhsb.usuhs.mil.
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