Growth of Escherichia coli and Salmonella typhimurium on high-pH beef packed under vacuum or carbon dioxide.

A strain each of Escherichia coli and Salmonella typhimurium, were inoculated onto samples of high-pH (greater than 6.0) beef. Samples were packaged under vacuum or CO2 and stored at 8, 10, 12, 15, 20 or 30 degrees C. In vacuum packs, E. coli and S. typhimurium grew at all storage temperatures. At temperatures between 8 and 12 degrees C inclusive, both organisms grew at rates less or no more than those of the spoilage flora after significant lag periods. At temperatures of 15 degrees C or above, growth rates were equal to or greater than those of the spoilage flora, and lag periods were insignificant. In CO2 packs, neither organism grew at 8 degrees C, and S. typhimurium did not grow at 10 degrees C. Subsequent tests showed that E. coli did not grow at 9 degrees C, nor S. typhimurium at 11 degrees C. At 12 degrees C, both organisms grew, after prolonged lags, at rates markedly slower than that of the spoilage flora. At 15 degrees C, their growth rates were similar to that of the spoilage flora. At higher temperatures, both organisms grew without significant lags at rates greater than that of the spoilage flora.

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.

Incidence and coincidence of Listeria spp., motile aeromonads and Yersinia enterocolitica on ready-to-eat fleshfoods.

A survey for the presence of Listeria spp., Yersinia enterocolitica and motile aeromonads in 203 samples of ready-to-eat fleshfoods purchased from retail outlets was conducted. Overall, 39.4%, 3.4% and 23.2% of samples were positive for the presence of Listeria spp., Y. enterocolitica and motile aeromonads respectively. Two factors have been identified as contributing to contamination of fleshfoods by these cold-tolerant bacteria. These are (i) the method of sale; delicatessen-bought foods were notably more contaminated than similar products bought pre-packaged, and (ii) the method of preservation. For motile aeromonads fermented foods were the least contaminated, whereas smoked and cooked products had similar incidence rates. For L. monocytogenes, significantly more (41.9%) smoked products were contaminated than fleshfoods preserved by other methods. For Y. enterocolitica, only cooked products were contaminated. In the case of cooked fleshfoods it must be assumed that most contamination occurs post-cooking and that contamination rates are increased by poor food handling procedures. Of the three possible pairwise combinations of these organisms, the coincidence of Y. enterocolitica and motile aeromonads was the only one that differed significantly from a random distribution (P less than 0.001), indicating that fleshfoods contaminated with Y. enterocolitica are probably also contaminated by motile aeromonads.

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.

Microbial spoilage of whole sheep livers.

When liver treated with antibiotics to inhibit microbial growth were held at 10 degrees C, the initial high pH (6.4) declined as lactic acid accumulated throughout the storage period of 10 days. The glycogen content also declined, but the glucose concentration in the tissues remained high. When livers were allowed to spoil at 10 degrees C, distinct but variable floras developed within the tissues, in the drip, and on the upper surface. Deep-tissue floras were composed of anaerobic and facultative organisms (Lactobacillus, Enterobacter, Aeromonas); surface floras were generally dominated by strictly aerobic organisms (Pseudomonas, Acinetobacter); drip floras contained variable proportions of organisms of all three types, but the facultatively anaerobic Enterobacter were usually present as a major component. Spoilage occurred after 4 to 6 days with the development of visible discrete colonies on the upper surface without spoilage odors being evident. Changes in tissue and drip composition due to microbial activity could be detected only when spoilage had reached an advanced stage.