Psychrotrophic Clostridium Research Articles

Influence of culture media on the recovery of psychrotrophic Clostridium spp. associated with the spoilage of vacuum-packed chilled meats

This study was undertaken to determine the influence of culture media on the quantitative recovery of vegetative cells and spores of psychrotrophic Clostridium spp. associated with the spoilage of chilled meats. For recovery of vegetative cells and spores (presumptive counts), 24 h or 48 h broth cultures in Peptone Yeast Extract Glucose Starch (PYGS) broth were used; for spore counts, concentrated spore suspensions derived from 35-day cultures were used. For presumptive counts, seven non-selective and eight selective media were tested. Recovery of psychrotrophic clostridia with optimum growth temperatures between 15°C and 20°C was best with non-selective media, such as Peptone Yeast Extract Glucose Starch (PYGS) agar with lysozyme; recovery of clostridia with growth optima between 25°C and 30°C was best with selective media, such as Shahidi Ferguson Perfringens (SFP) agar. For organisms with the lower optimum growth temperature (heat-sensitive group) spore recovery after heat treatment (80°C for 10 min) was best if a 2 M (pH 10) thioglycollate treatment (10 min at 45°C) was used, followed by plating onto a lysozyme- or egg-yolk-containing medium. For organisms with the higher optimum growth temperature (heat-resistant group), spore recovery was best on Glucose Starch agar without added lysozyme. The diversity among psychrotrophic Clostridium spp. associated with chilled meat spoilage precludes the identification of a single `best' recovery medium or technique. Consequently, a variety of complementary selective techniques and media must be used if comprehensive recovery is to be assured.

Prevalence of cold‐tolerant clostridia associated with vacuum‐packed beef and lamb stored at abusive and chill temperatures

A survey was conducted for the presence of cold‐tolerant (i.e. capable of growing at less than 5°C) Clostridium spp. in fresh vacuum‐packed beef and lamb obtained from nine export meat plants. Prevalence was determined before and after storage at abusive (15°C) and non‐abusive (‐1.5°C) temperatures, and instances of pack failure by “blowing” were recorded. Overall, only three samples (6.7%) were positive for the presence of this group of micro‐organisms on initial testing. After storage at 15°C for 8 weeks, cold‐tolerant clostridia were found in 51.1% of samples, all of which had “blown”. After storage at ‐1.5°C for 12 weeks, only 2 samples (4.4%) accumulated significant amounts of gas, and both contained cold‐tolerant clostridia. With vacuum‐packed product stored at 15°C, approximately 29% of the clostridial strains isolated at 15°C were cold‐tolerant species capable of growing at less than 5°C. However, none of them were able to grow at ‐1.5°C. Only psychrophilic and psychrotrophic clostridia were isolated from fresh samples and those stored at ‐1.5°C.

Psychrotrophic Clostridium spp. associated with ‘blown pack’ spoilage of chilled vacuum-packed red meats and dog rolls in gas-impermeable plastic casings

‘Blown pack’ spoilage of vacuum-packed chilled beef, lamb and venison, and of a cooked meat product, chilled dog rolls packed in an oxygen-impermeable plastic casing, was characterised by sensory, chemical and microbiological analysis. Investigation of the probable causative agents led to the isolation of eight strains of psychrotrophic clostridia. Three strains have been provisionally identified as C. difficile, C. beijerinckii and C. lituseburense; the other five remain unidentified. In inoculation studies only one isolate produced significant amount of gas on meat, causing pack ‘blowing’. It is, therefore, possible that ‘blown pack’ spoilage involves a synergism with one or more other organisms.

Association of psychrotrophic Clostridium spp. with deep tissue spoilage of chilled vacuum-packed lamb

Early spoilage of commercial vacuum-packed chilled lamb legs was manifested as an objectionable ‘cheesy’, deep tissue odour that became evident when a cut was made into the stifle joint. Investigation of the probable causative agents led to the isolation of two psychrotrophic strains of clostridia. The isolates could not be identified using traditional identification schemes. One isolate was able to produce strong, objectionable ‘cheesy’ odours in deep tissues of artificially inoculated beef.

Growth and heat resistance of psychrotrophic Clostridium botulinum in relation to ‘sous vide’ products

The processing stages used in ‘sous vide’ technology, i.e. vacuum packaging, mild pasteurization treatments and extended storage at chill temperatures may select for survival and growth of psychrotrophic strains of Clostridium botulinum. This organism can produce toxin within 31 days at 3.3 °C and within 12 days at 8.0 °C but is relatively heat-sensitive and may therefore be destroyed using a suitable pasteurization treatment. This paper discusses the growth and heat resistance characteristics of psychrotrophic C. botulinum in sous vide foods with recommendations for the safe manufacture of these products.

Characterization of a psychrotrophic Clostridium causing spoilage in vacuum-packed cooked pork: description of Clostridium algidicarnis sp. nov.

A Clostridium species causing spoilage of vacuum-packed refrigerated pork was isolated and characterized. The unknown organism differed phenotypically from other clostridial species usually associated with spoilage. Phylogenetic analyses based on 16S rRNA gene sequencing demonstrated that the psychrotroph represents a distinct line of descent within the genus Clostridium. It is proposed that the organism be classified as a new species of the genus Clostridium, Clostridium algidicarnis.

Incidence and growth of psychrotrophic Clostridium botulinum in foods

Over 500 samples of refrigerated packaged foods currently on sale in the UK were examined for the incidence of psychrotrophic strains of Clostridium botulinum. None of the samples was found to contain psychrotrophic C. botulinum. Botulinum toxin was not detected in inoculated samples of carrots, jacket potatoes, lasagne or smoked trout fillets after incubation at 4°C and 10°C for 3 weeks. In inoculated whole trout, however, it was found that toxin production could occur within 1 week at 10°C.

Characteristics of Psychrotrophic Clostridium laramie Causing Spoilage of Vacuum-packaged Refrigerated Fresh and Roasted Beef

A Clostridium sp., associated with an unusual spoilage of vacuum-packaged refrigerated uncooked (fresh) and roasted beef, was isolated as a pure culture from the spores in spoiled beef. The pure culture was used to study important characteristics and to differentiate it from other clostridial species usually found in beef. The biochemical characteristics, volatile fatty acid and soluble-protein profiles, temperatures and pHs of growth, and temperatures of sporulation, germination, and destruction of the isolate were distinctly different from other Clostridium spp. studied. It is not toxigenic and has 26% guanine plus cytosine. The isolate is a new species and is named Clostridium laramie.

A comparative study on the heat stability of triosephosphate isomerase in psychrophilic, psychrotrophic, and mesophilic Clostridia

The temperature stability of triosephosphate isomerase (EC 5.3.1.1) in the cell-free extracts of psychrophilic, psychrotrophic, and mesophilic Clostridium species has been investigated. Even though this enzyme was found to be heat labile in the psychrophilic isolates, no detectable loss in activity was evident when cell-free extracts were heated for 1/2 h at the maximum temperature of growth for the organisms. Two organisms, each with a maximum growth temperature of 23 degrees C, showed different heat stability of triosephosphate isomerase. However, a trend is evident that as the maximum growth temperature increases, the thermostability also increases. It is suggested that the heat liability of this enzyme is not a controlling factor in psychrophilism, but rather an adaptation to the cold habitat of these organisms.

Low-temperature-growing clostridia from marine sediments

Marine sediments inoculated into cooked meat medium were enriched for 5 months at 0–5 °C. Organisms isolated and purified were tested for growth at low temperatures, and those growing only anaerobically at 5 °C and below were retained for further study. The growth–temperature range was determined by growing 18 isolates on a temperature-gradient incubator over a temperature range of 0 to 34 °C. On the bases of minimum, optimum, and maximum growth temperatures, the 18 isolates were separated into obligate and facultative psychrophilic and psychrotrophic clostridia. The DNA was extracted from cells grown at 12 °C and the percentage of G + C for all the isolates fell within the range characteristic of Clostridium species. The volatile alcohols and acids produced on a glucose medium were detected by gas chromatography. Ten of the isolates produced no alcohols and only acetic and butyric acids. One isolate produced butanol and acetic and butyric acids. The remaining seven isolates produced one or two alcohols, ethanol and butanol, and up to six acids. The 18 isolates fell into distinct groups with a close relationship between growth–temperature range and volatile alcoholic and acidic products. Biochemical tests showed that the isolates resembled Clostridium species described in the literature; however, they were not like any known species and were not named.