Escherichia coli K5 capsule expression enhances colonization of the large intestine in the gnotobiotic rat

Abstract

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.

Transcriptional regulation through RfaH contributes to intestinal colonization byEscherichia coli

“…To get more insight in the mechanism of the RfaHdependent effect on colonization, capsular or LPS deep-rough mutants as well as double mutants were used in additional mixed infections. In contrast to former observations [34], we could detect no positive role of group II capsules (K5 in case of strain Nissle1917 and K1 in strain IHE3034) in colonization. On the other hand, deep-rough mutants (waaG) of the same strains are highly impaired in their intestinal colonization compared to their wild type strains (Fig.…”

“…Recently a deep-rough mutant of the commensal E. coli K-12 strain MG1655 was shown to be reduced in its ability to colonize the mouse intestinal tract due to increased tendency to clump in the intestinal mucus [27]. Similarly, capsular polysaccharides have been proposed to contribute to intestinal colonization by several Gram-negative pathogens including E. coli [33,34]. In Vibrio cholerae O139 both LPS and capsular polysaccharide play an important role in the colonization process [35].…”

Klebsiella pneumoniae Capsule Expression Is Necessary for Colonization of Large Intestines of Streptomycin-Treated Mice

“…In spite of the fact that the majority of K. pneumoniae clinical isolates produce a very characteristic, heavy polysaccharide capsule (K antigen) covering the entire bacterial surface, very few studies have been performed to assess the role of this component during colonization of mucosal surfaces. The importance of Escherichia coli K5 capsule expression was demonstrated in gnotobiotic rats (11), whereas the K. pneumoniae capsule was found to play no role in colonization of the gut of germfree chickens (2).…”

Functional genotypes are associated with commensal Escherichia coli strain abundance within‐host individuals and populations

“…Extensive research into pathogenic strains has led to the isolation and characterization of numerous functional genes, initially described for their association with virulence (for example see Johnson et al 2002;Spurbeck et al 2011Spurbeck et al , 2012. These genes belong to the variable portion of the E. coli genome (Touchon et al 2009) and encode a range of different classes of proteins that have been associated with strain colonization success and persistence (Wold et al 1992;Herias et al 1997;Nowrouzian et al 2001Nowrouzian et al , 2006Johnson et al 2008a;Schierack et al 2008;Lasaro et al 2009;Diard et al 2010). Thus, these genes are good candidates for functional gene effects on strain abundance.…”