The role of fimbriae and flagella in the colonization, invasion and persistence of Escherichia coli O78 : K80 in the day-old-chick model

To understand the role of flagella and fimbriae of Escherichia coli O78:K80 in avian colibacillosis, day-old chicks were dosed orally with defined afi mbriate and or aflagellate mutants and colonization, invasion and persisten ce compared with that of the wild-type. In an invasion model, chicks were d osed with 1 x 10(5) c.f.u. of a single strain and mutants defective for typ e 1 fimbriae, curli fimbriae or flagella colonized livers by 24 h although the numbers of bacteria present were significantly less than the wild-type, Mutants colonized between 50 and 75 % of spleens whereas the wild-type col onized 100 % of spleens. Additionally, the numbers of mutant bacteria in co lonized spleens were significantly less than the wild-type. Surprisingly, m utants defective for the elaboration of more than one appendage were no mor e attenuated than single mutants. In a persistence model, chicks were dosed with 1 x 10(2) c.f.u. of a single strain and mutants defective for type 1 or curli or flagella or any combination thereof persisted as assessed by cl oacal swabbing for 5 weeks of the experiment less well than the wild-type. In an additional persistence model, chicks were dosed with 5 x 10(2) c.f.u. of each of wild-type and one mutant together. All mutants were significant ly less persistent than the wild-type (P < 0.001) and one mutant which lack ed type 1, curli and flagella, was eliminated within 2 weeks. Analysis of t he trends of elimination indicated that flagella contributed to persistence more than curli, which contributed more than type 1 fimbriae. Here was evi dence for a major role in colonization, invasion and persistence played by type 1, curli and flagella.