Identification and differentiation of Campylobacter fetus subspecies by PCR.

The species Campylobacter (C.) fetus is divided into the subspecies venerealis and fetus, which differ in epidemiology and clinical importance. The differences between these subspecies make an accurate distinction essential. Differentiation of C. fetus by traditional microbiological methods is only based on two reactions (tolerance to glycin, Na selenite reduction), in which C. fetus ssp. venerealis reacts negatively. However, the value of both reactions is limited. We used a specific PCR-based assay for identifying and differentiating the two C. fetus subspecies, which was recently developed by HUM et al. (1997). In this assay, a 764 bp amplicon is produced using primers MG3F and MG4R for both subspecies of C. fetus. In contrast to HUM et al. (1997), this amplicon was approximately 200 bp smaller. This discrepancy can't be explained. Afterwards, the primers VenSF and VenSR are used for differentiation. The identification of the subspecies venerealis is based on the presence of a 142 bp amplicon, which is not formed with subspecies fetus. The type strains of both C. fetus subspecies were used as-positive controls. Non-specific reactions were not observed. In this PCR assay, 73 field strains were investigated (among them 24 C. fetus ssp. venerealis, 26 C. fetus ssp. fetus). In these investigations, the method has proved its diagnostic suitability. The results of the traditional microbiological differentiation of the C. fetus field strains could be confirmed by the PCR assay. In future, the traditional phenotypic characterization of C. fetus subspecies remains indispensable, but this PCR assay constitutes a valuable method for the confirmation of these results.