Abstract
A multilocus sequence typing (MLST) scheme that uses the same loci as a previously described system for Campylobacter jejuni was developed for Campylobacter coli. The C. coli-specific primers were validated with 53 isolates from humans, chickens, and pigs, together with 15 Penner serotype reference isolates. The nucleotide sequence of the flaA short variable region (SVR) was determined for each isolate. These sequence data were compared to equivalent information for 17 C. jejuni isolates representing the known genetic diversity of this species. C. coli and C. jejuni share approximately 86.5% identity at the nucleotide sequence level within the MLST loci. There is evidence of genetic exchange of the housekeeping genes between the two species, but at a very low rate; only one sequence type from each species showed evidence of imported DNA. The flaA gene was more variable and has been exchanged many times between the two species, making it an unreliable marker for species identification but useful for distinguishing closely related strains. All but 3 of 21 human C. coli clinical isolates were distinct, according to the combined MLST and SVR sequences. The use of a common MLST scheme allows direct comparisons of the population biology and molecular epidemiology of these two closely related human pathogens.