Epidemiology, relative invasive ability, molecular characterization, and competitive performance of Campylobacter jejuni strains in the chicken gut

Abstract

One hundred forty-one Campylobacter jejuni isolates from humans with diarrhea and 100 isolates from retailed poultry meat were differentiated by flaA typing. The bacteria were isolated in a specific geographical area (Dunedin) in New Zealand over a common time period. Twenty nine flaA types were detected, one of which (flaA restriction fragment length polymorphism type 15 [flaA-15]) predominated among isolates from humans ( approximately 30% of isolates). This strain was of low prevalence (5% of isolates) among poultry isolates. flaA-15 strains were five to six times more invasive of HEp2 cells in an in vitro assay than a flaA type (flaA-3) that was commonly encountered on poultry meat (23% of isolates) but was seldom associated with human illness (5%). Competitive-exclusion experiments with chickens, utilizing real-time quantitative PCR to measure the population sizes of specific strains representing flaA-15 (T1016) and flaA-3 (Pstau) in digesta, were carried out. These experiments showed that T1016 always outcompeted Pstau in the chicken intestine. Genomic comparisons of T1016 and Pstau were made using DNA microarrays representing the genome of C. jejuni NCTC 11168. These comparisons revealed differences between the strains in the gene content of the Cj1417c-to-Cj1442c region of the genome, which is associated with the formation of capsular polysaccharide. The strains differed in Penner type (T1016, O42; Pstau, O53). It was concluded that poultry meat was at least one source of human infection with C. jejuni, that some Campylobacter strains detected in poultry meat are of higher virulence for humans than others, and that bacterial attributes affecting strain virulence and commensal colonization ability may be linked.

FIG. 1.

Comparison of flaA types detected among clinical isolates obtained in 1996 and 1997 (a), poultry meat isolates obtained in 1998 (b), or clinical isolates obtained in 1998 (c). The prevalence of each strain is shown as wedges of pie graphs.

FIG. 2.

Hydropathic profiles of T1016 and Pstau FlaA proteins (Kyte-Doolittle calculation over a window length of 19).

FIG. 3.

Alignment of predicted amino acid sequences of FlaA proteins. Campylobacter strains are listed on the left. The asterisk indicates identity, whereas the colon and period indicate amino acid similarities. Boldface letters show conserved residues in Pstau and T1016 that have been shown to be glycosylated in 81-176 and VC167. Underlined letters indicate residues that may be modified given the hydrophobic nature of surrounding residues and/or conserved localization with a S/T residue that has been shown to be modified in 81-176 or VC167. Red letters indicate hydrophobic residues, whereas lilac and blue indicate residues that are negatively and positively charged, respectively. Numbers at right facilitate amino acid positioning.