PCR detection of psychrophilic Clostridium spp. causing 'blown pack' spoilage of vacuum-packed chilled meats.

Abstract

To develop a practical molecular procedure that directly, without isolation, and specifically detects the presence of clostridia which cause 'blown pack' spoilage of vacuum-packed meat. Primer sets and PCR amplification procedures were developed that detect the presence of 16S rDNA gene and/or 16S-23S rDNA internal transcribed spacer fragments of 'blown pack' causing clostridia in meat. The specificity of the developed procedures was evaluated with DNA obtained from close phylogenetic neighbours of 'blown pack' causing clostridia, food clostridia and common meat spoilage microorganisms. The sensitivity of detection was assessed in non-enriched and low-temperature-enriched beef mince inoculated with serially diluted pure cultures of Clostridium estertheticum DSMZ 8809T and Cl. gasigenes DB1AT. The efficacy of detection procedures was evaluated for naturally contaminated vacuum-packed meat samples. Three primer sets, 16SE, 16SDB and EISR, produced amplicons of the expected size with DNA templates from target clostridia, but failed to yield PCR products with DNAs from any other microorganisms tested. With 16SE and 16SDB primers, minimum levels of detection were 104 CFU g(-1) for non-enriched, and 102 CFU g(-1) for enriched meat samples. Based on the established specificity of these primers, as well as DNA sequencing of amplicons, Cl. gasigenes was confirmed as the causative agent of 'blown pack' spoilage in two packs, and Cl. estertheticum as the causative agent in the third. The developed method can be used for rapid detection of 'blown pack' causing clostridia in commercial blown packs, or following low temperature enrichment, for detection of these microorganisms in meat containing as few as 100 clostridial cells per gram. The paper reports practical procedures that can be used for rapid confirmation of the causative agents of clostridial 'blown pack' spoilage in commercial spoiled packs, or for detection of psychrophilic clostridia in epidemiological trace back of 'blown pack' spoilage incidents in meat processing plants.