Effects of lipooligosaccharide inner core truncation on bile resistance and chick colonization by Campylobacter jejuni.

Campylobacter jejuni is the most common bacterium that causes diarrhea worldwide, and chickens are considered the main reservoir of this pathogen. This study investigated the effects of serial truncation of lipooligosaccharide (LOS), a major component of the outer membrane of C. jejuni, on its bile resistance and intestinal colonization ability in chickens. Genes encoding manno-heptose synthetases or glycosyltransferases were inactivated to generate isogenic mutants. Serial truncation of the LOS core oligosaccharide caused a stepwise increase in susceptibilities of two C. jejuni strains, NCTC 11168 and 81-176, to bile acids. Inactivation of hldE, hldD, or waaC caused severe truncation of the core oligosaccharide, which greatly increased the susceptibility to bile acids. Both wild-type strains grew normally in chicken intestinal extracts, whereas the mutants with severe oligosaccharide truncation were not detected 12 h after inoculation. These mutants attained viable bacterial counts in the bile acid-free extracts 24 h after inoculation. The wild-type strain 11-164 was present in the cecal contents at >10(7) CFU/g on 5 days after challenge infection and after this time period, whereas its hldD mutant was present at <10(3) CFU/g throughout the experimental period. Trans-complementation of the hldD mutant with the wild-type hldD allele completely restored the in vivo colonization level to that of the wild-type strain. Mutants with a shorter LOS had higher hydrophobicities. Thus, the length of the LOS core oligosaccharide affected the surface hydrophobicity and bile resistance of C. jejuni as well as its ability to colonize chicken intestines.