ESCHERICHIA-COLI K5 CAPSULE EXPRESSION ENHANCES COLONIZATION OF THE LARGE-INTESTINE IN THE GNOTOBIOTIC RAT

The role of capsule expression in the capacity of Escherichia coli to colonize in the large intestinal environment was studied in a gnotobio tic rat model, The rats were given perorally a mixture of two mutant s trains differing in K5 expression, After 2 weeks, the rats were sacrif iced, and subsequently intestinal contents, intestinal mucosae, and me senteric lymph nodes were homogenized and bacterial numbers were quant ified, Two E. coli mutant pairs were used, the first pair (972-998) la cking 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] fo r the second pair, respectively), The results were confirmed by serolo gy showing a K5 phenotype for practically all isolates, The bacterial population associated with the mucosa was similar to that in the lumin al 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 expre ssion of P fimbriae remained high whereas only a minority of the isola tes expressed type 1 fimbriae, The results suggest that capsule expres sion and P fimbriae enhance intestinal colonization by E. coli and tha t these virulence factors, by increasing bacterial densities in the in testine, secondarily increase translocation.