Potential risk of botulinum neurotoxin - producing clostridia occurrence in canned fish

Abstract

Introduction: Heat treatment is indispensable in fish canning to provide an acceptable shelf life. Its optimisation reduces the risk of the presence of Clostridium botulinum spores, which could potentially cause botulism cases. This study evaluated canned fish samples for botulism neurotoxin (BoNT)-producing clostridia contamination and can bulging through microbiological contaminant growth. A new analytical approach was developed for detection of such clostridia and phenotypically similar species. Material and Methods: A total of 70 canned fish samples suspected of exhibiting bulging features were analysed. Culture methods were used to detect clostridia. The isolates obtained were evaluated on the basis of the exhibited phenotypic characteristics. Also, PCRs were used for the detection of genes determining BoNT production (non-toxic non-haemagglutinin (ntnh) genes) and the amplification of conservative 16S rDNA genes, which were Sanger sequenced. The obtained sequences were analysed using the Basic Local Alignment Search Tool. Results: Clostridium genus species were isolated from 17 (24%) bulging and organoleptically changed samples. No ntnh genes were present in these isolates; however, sequencing confirmed the presence of C. sporogenes, a species with close affinity to C. botulinum. Conclusion: To eliminate the threat of foodborne botulism, laboratory diagnostic techniques must detect species of the Clostridium genus and elucidate their ability to produce BoNTs. Although Clostridium botulinum is the most common cause of botulism, the possibility may not be ignored that non-pathogenic Clostridium species may acquire botulinum toxigenicity. The similarity between the isolated strains of C. sporogenes and C. botulinum should be incorporated in the optimisation of heat treatment to guarantee a sterilised, microbiologically safe product.