The growth of Listeria monocytogenes, Aeromonas hydrophila and Yersinia enterocolitica on sliced roast beef packaged under vacuum or saturated CO2 controlled atmosphere conditions was measured. At −1.5°C, the pathogens declined in numbers in the controlled atmosphere packs but were able to grow under vacuum packaging. At 3°C, growth occurred, with maximum numbers being reached at the end of the product's storage life. The increased shelf life of sliced roast beef incubated under a carbon dioxide controlled atmosphere compared to vacuum-packaged beef did not, therefore, bring with it a concomitant risk associated with the increased growth of these three pathogens over the extended storage period.

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A total of 182 Aeromonas hydrophila strains isolated from environmental (food and water) and clinical (stool and other sources) samples taken in mainland Australia, Tasmania and New Zealand were assigned to one of three DNA/DNA hybridization groups (HGs) on the basis of biochemical characteristics, and tested with regard to their ability to produce virulence factors. Strains from HG2 were rarely isolated; strains from HG1 were most commonly isolated from clinical sources; and strains from HG3 formed the majority of environmental strains. There was no correlation of HG to geographic source. Strains from HG2 infrequently produced virulence factors. Strains from HG1 were more likely to produce virulence factors if they came from a clinical source. Overall, strains from mainland Australia produced virulence factors more frequently than those from Tasmania or New Zealand. Strains from HG1 may be of more clinical significance than strains from the other two HGs.

Values were obtained for the lag times of a strain of the meat spoilage bacterium Pseudomonas fragi under a variety of cultural conditions by analyzing optical density (OD) and viable count (VC) data using the Gompertz equation. Lag times produced from OD data were shorter than those derived from VC data. Observations showed that during the lag phase, cell length increased before the cells began to divide, explaining the apparent earlier resolution of lag phase observed with the OD measurement technique. By linear regression the general equation:where A = 0.344 and B = 0.868 was derived to interconvert OD lag times and VC lag times. This equation was applied to predicted lag times derived from models that had been constructed using optical density data and that are used to predict growth kinetics of cold-tolerant pathogens on foods. With this adjustment, the models demonstrated an improved predictive ability when compared to measured values for growth of these pathogens on foods.