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Infect. Immun., 02 1997, 531-536, Vol 65, No. 2
MV Herias, T Midtvedt, LA Hanson and AE Wold
The role of capsule expression in the capacity of Escherichia coli to
colonize in the large intestinal environment was studied in a gnotobiotic
rat model. The rats were given perorally a mixture of two mutant strains
differing in K5 expression. After 2 weeks, the rats were sacrificed, and
subsequently intestinal contents, intestinal mucosae, and mesenteric lymph
nodes were homogenized and bacterial numbers were quantified. Two E. coli
mutant pairs were used, the first pair (972- 998) lacking the O-specific
side chain and the second pair (973-997) carrying the O75
lipopolysaccharide. The K5+ mutants established themselves at a higher
level than the K5- mutants (10(9) versus 10(6) CFU/g [P < 0.001] for the
first pair and 10(9) versus 10(8) CFU/g [P < 0.01] for the second pair,
respectively). The results were confirmed by serology showing a K5+
phenotype for practically all isolates. The bacterial population associated
with the mucosa was similar to that in the luminal contents with respect to
the proportions of the respective mutants, and translocation occurred in
numbers proportional to the intestinal population densities of the
respective mutants. All mutants were able to express type 1 as well as P
fimbriae. After colonization, the expression of P fimbriae remained high
whereas only a minority of the isolates expressed type 1 fimbriae. The
results suggest that capsule expression and P fimbriae enhance intestinal
colonization by E. coli and that these virulence factors, by increasing
bacterial densities in the intestine, secondarily increase translocation.
Copyright © 1997, American Society for Microbiology
Escherichia coli K5 capsule expression enhances colonization of the large intestine in the gnotobiotic rat
Department of Clinical Immunology, University of Goteborg, Sweden. veronica.herias@immuno.gu.se
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