Klebsiella pneumoniae capsule expression is necessary for colonization of large intestines of streptomycin-treated mice

Abstract

The role of the Klebsiella pneumoniae capsular polysaccharide (K antigen) during colonization of the mouse large intestine was assessed with wild-type K. pneumoniae LM21 and its isogenic capsule-defective mutant. When bacterial strains were fed alone to mice, the capsulated bacteria persisted in the intestinal tract at levels of 10(8) CFU/g of feces while the capsule-defective strain colonized at low levels, 10(4) CFU/g of feces. In mixed-infection experiments, the mutant was rapidly outcompeted by the wild type. In situ hybridization on colonic sections revealed that bacterial cells of both strains were evenly distributed in the mucus layer at day 1 after infection, while at day 20 the wild type remained dispersed and the capsule-defective strain was seen in clusters in the mucus layer. These results suggest that capsular polysaccharide plays an important role in the gut colonization ability of K. pneumoniae.

FIG. 1

Colonization by wild-type K. pneumoniae LM21 (■) and its capsule-defective mutant, K. pneumoniae LM21(cps) (▴), of the intestines of streptomycin-treated mice. The strains were fed separately to each of three streptomycin-treated mice. Symbols for day 0 represent the sizes of the inocula. At the indicated times, fecal samples were plated as described in the text. The detection limit is marked by a broken line. Bars represent standard errors of the means.

FIG. 2

Co-colonization by wild-type K. pneumoniae LM21 (■) and its capsule-defective mutant, K. pneumoniae LM21(cps) (▴), of the intestines of streptomycin-treated mice. (A) The strains were fed simultaneously at 10⁸ CFU to streptomycin-treated mice. (B) The strains were fed simultaneously at 10⁵ CFU to streptomycin-treated mice. Symbols for day 0 represent the sizes of the inocula. At the indicated times, fecal samples were plated as described in the text. Bars represent standard errors of the means.

FIG. 3

Colonic sections of mice fed wild-type K. pneumoniae LM21 (A) and the K. pneumoniae LM21(cps) capsule-defective mutant (B) on day 1 after onset of infection. (Left) Phase-contrast picture of the corresponding area of in situ hybridization. (Right) In situ hybridization with fluorescence-labeled oligonucleotide probes. K. pneumoniae bacteria appear red, while other eubacteria appear green. The colonic epithelium (Ep) is fluorescent because of the autofluorescence of the eucaryotic tissue. Bars, 10 μm.

FIG. 4

Colonic sections of mice fed wild-type K. pneumoniae LM21 (A) and the K. pneumoniae LM21(cps) capsule-defective mutant (B) on day 20 after infection. (Left) Phase-contrast picture of the corresponding area of in situ hybridization. (Right) In situ hybridization with fluorescence-labeled oligonucleotide probes. K. pneumoniae bacteria appear red, while other eubacteria appear green. The colonic epithelium (Ep) is fluorescent because of the autofluorescence of the eucaryotic tissue. Bars, 10 μm.