Evaluation of a PCR Assay for Identification and Differentiation of Campylobacter Fetus Subspecies

Objective: To evaluate a polymerase chain reaction assay for identification of Campylobacter fetus and differentiation of the defined subspecies.

Design: Characterisation of bacterial strains by traditional phenotyping, polymerase chain reaction, a probabilistic identification scheme and macrorestriction profiling using pulsed field gel electrophoresis.

Procedure: The results of identification of 99 bacterial strains as determined by conventional phenotyping or by polymerase chain reaction were compared. Two of these were type strains of C fetus subsp fetus and C fetus subsp venerealis; the remaining strains were field isolates putatively identified as C fetus. In cases where the subspecies identity was disputed, isolates were identified by means of a probabilistic identification scheme and by macrorestriction profiling.

Results: The agreement between strain identities initially suggested by traditional phenotypic methods and the PCR assay was found to be 80.8%. The polymerase chain reaction proved to be a reliable technique for the species and subspecies identification of C fetus; equivocal results were obtained in only two instances. Initial misidentifications by conventional phenotyping methods were attributed to methodological differences used in various laboratories.

Conclusion: Our results indicate that misidentification of C fetus in routine diagnostic laboratories may be relatively common. The PCR assay evaluated gave rapid and reproducible results and is thus a valuable adjunctive method for the identification of C fetus and subsequent subspecies differentiation.