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Infection and Immunity, September 1999, p. 4367-4375, Vol. 67, No. 9
Microbiological Research Unit, Department of
Microbiology and Infectious Diseases, Royal Children's Hospital, and
Department of Microbiology and Immunology, University of Melbourne,
Parkville, Victoria 3052, Australia
Received 3 March 1999/Returned for modification 6 May 1999/Accepted 9 June 1999
Yersinia enterocolitica strains of biotype 1A are
increasingly being recognized as etiological agents of gastroenteritis. However, the mechanisms by which these bacteria cause disease differ
from those of highly invasive, virulence plasmid-bearing Y. enterocolitica strains and are poorly understood. We have
investigated several biotype 1A strains of diverse origin for their
ability to resist killing by professional phagocytes. All strains were rapidly killed by polymorphonuclear leukocytes but persisted within macrophages (activated with gamma interferon) to a significantly greater extent (survival = 40.5% ± 17.4%) than did
Escherichia coli HB101 (9.3% ± 0.7%; P = 0.0001). Strains isolated from symptomatic patients were
significantly more resistant to killing by macrophages (survival = 48.9% ± 19.5%) than were strains obtained from food or the
environment (survival = 32.1% ± 10.3%; P = 0.04). Some strains which had been ingested by macrophages or HEp-2
epithelial cells showed a tendency to reemerge into the tissue culture
medium over a period lasting several hours. This phenomenon, which we termed "escape," was observed in 14 of 15 strains of clinical origin but in only 3 of 12 nonclinical isolates (P = 0.001). The capacity of bacteria to escape from cells was not directly
related to their invasive ability. To determine if escape was due to
host cell lysis, we used a variety of techniques, including lactate dehydrogenase release, trypan blue exclusion, and examination of
infected cells by light and electron microscopy, to measure cell
viability and lysis. These studies established that biotype 1A Y. enterocolitica strains were able to escape from macrophages or
epithelial cells without causing detectable cytolysis, suggesting that
escape was achieved by a process resembling exocytosis. The observations that biotype 1A Y. enterocolitica strains of
clinical origin are significantly more resistant to killing by
macrophages and significantly more likely to escape from host cells
than are strains of nonclinical origin suggest that these properties
may account for the virulence of these bacteria.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Characterization of the Interaction between Yersinia
enterocolitica Biotype 1A and Phagocytes and Epithelial Cells
In Vitro
*
Corresponding author. Mailing address: Department of
Microbiology and Infectious Diseases, Royal Children's Hospital,
Parkville, Victoria 3052, Australia. Phone: (61-3) 9345-5741. Fax:
(61-3) 9345-5764. E-mail:
rbrowne{at}cryptic.rch.unimelb.edu.au.
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