Genetic diversity and relationships of Campylobacter species and subspecies

The existence of tremendous genetic diversity within Campylobacter species has been well documented. To analyse the population structure of Campylobacter and determine whether or not a clonal population structure could be detected, genetic diversity was assessed within the genus Campylobacter by multilocus enzyme electrophoresis of 156 isolates representing 11 species and subspecies from disparate sources. Analyses of electrophoretic mobility of 11 enzymes revealed 109 electrophoretic types (ETs) and 118 ETs when nulls were counted as an allele. Cluster analysis placed most ETs into groups that correlated with species. With nulls counted as alleles, 19 ETs were identified among 33 isolates of Campylobacter lari, 31 ETs among 34 isolates of Campylobacter coli and 43 ETs among 59 isolates of Campylobacter jejuni subsp. jejuni. Nine C. jejuni subsp. jejuni isolates, confirmed as this species by DNA-DNA hybridization, were hippuricase-negative. Reported linkage analyses were done with nulls ignored. Scores for mean genetic diversity (H) were high for the total population (mean H = 0.802). Allelic mismatch-frequency distributions and allelic tracing pointed to possible genetic exchange between subpopulations. C. lari appears to be a panmictic species. Some pairs of species shared multiple alleles of certain loci, possibly indicating genetic exchange between species. Of the species tested, C. jejuni appeared to be the most active in sharing alleles. However, there was evidence of variable involvement in recombination by the different loci. Linkage analysis of loci in C. jejuni and C. coli revealed a clonal framework, with some loci tightly linked to each other. The loci appeared to occur in linkage groups or islands. Campylobacter may have a clonal framework with other portions of the genome involved in frequent recombination. Population genetic structure among Campylobacter is inconclusive and it remains to be seen if pathogenic types can be identified.