EVALUATION OF PCR AND DNA HYBRIDIZATION PROTOCOLS FOR DETECTION OF VIABLE ENTEROTOXIGENIC CLOSTRIDIUM-PERFRINGENS IN IRRADIATED BEEF

The sensitivity of DNA hybridization and polymerase chain reaction (PC R), was evaluated in irradiated cooked and raw beef samples. A membran e-based colony hybridization assay and a PCR protocol, both with speci ficity for the enterotoxin A gene of Clostridium perfringens, were com pared with viable plate counts. The results of the colony hybridizatio n procedure were in agreement with viable plate counts for defection a nd enumeration of enterotoxigenic C. perfringens. The PCR procedure co mbined a 4 h enrichment followed by a nucleic acid extraction step and assessed the amplification of 183 and 750 base pair enterotoxin gene targets. Detection of C. perfringens by PCR did not show a reliable co rrelation with viable plate counts or the colony hybridization assay. C. perfringens killed by irradiation were not detected by the plate co unt or colony hybridization methods; however, killed cells were detect ed with the PCR technique. By relying on the growth of viable cells fo r detection and/or enumeration, the colony hybridization and plate cou nt methods provided a direct correlation with the presence of viable b acteria.