Population genetics of human and animal enteric Campylobacter strains.

A total of 125 strains of Campylobacter jejuni and Campylobacter coli from human and animal hosts were analyzed by multilocus enzyme electrophoresis. Ten genetic loci were characterized by the electrophoretic mobilities of their products, and all were found to be polymorphic. The nine loci considered for genetic analysis had an average allele number of 6.9 and a mean genetic diversity of 0.634. The strains were grouped into 64 electrophoretic types (ETs) forming two principal clusters; the first cluster consisted of 50 ETs represented by 104 isolates of C.jejuni, and the second included 14 ETs represented by 21 isolates of C. coli. The genetic distance between the two species was 0.939. The data support the conclusions that (i) campylobacteriosis caused by C. jejuni and C. coli is a zoonosis, (ii) human and animal strains do not constitute subpopulations, and (iii) every animal strain may be considered a potential human pathogen. The frequency of intraspecies gene transfer seems to be moderately high whereas interspecies gene transfer is very rare at best, which suggests the existence of a biological barrier between C. jejuni and C. coli.