Genetic Divergence of Campylobacter fetus Strains of Mammal and Reptile Origins

Campylobacter fetus is a gram-negative bacterial pathogen of both humans and animals. Two subspecies have been identified, Campylobacter fetus subsp. fetus and Campylobacter fetus subsp. venerealis, and there are two serotypes, A and B. To further investigate the genetic diversity among C. fetus strains of different origins, subspecies, and serotypes, we performed multiple genetic analyses by utilizing random amplification of polymorphic DNA (RAPD), pulsed-field gel electrophoresis (PFGE), and DNA-DNA hybridization. All 10 primers used for the RAPD analyses can distinguish C. fetus strains of reptile and mammal origin, five can differentiate between C. fetus subsp. fetus and C. fetus subsp. venerealis strains, and four showed differences between type A and type B isolates from mammals. PFGE with SmaI and SalI digestion showed varied genome patterns among different C. fetus strains, but for mammalian C. fetus isolates, genome size was well conserved (mean, 1.52 ± 0.06 Mb for SmaI and 1.52 ± 0.05 Mb for SalI). DNA-DNA hybridization demonstrated substantial genomic-homology differences between strains of mammal and reptile origin. In total, these data suggest that C. fetus subsp fetus strains of reptile and mammal origin have genetic divergence more extensive than that between the two subspecies and that between the type A and type B strains. Combining these studies with sequence data, we conclude that there has been substantial genetic divergence between Campylobacter fetus of reptile and mammal origin. Diagnostic tools have been developed to differentiate among C. fetus isolates for taxonomic and epidemiologic uses.