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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Bacteria are confined to the surface of meat during the logarithmic phase of growth. When proteolytic bacteria approach their maximum cell density, extracellular proteases secreted by the bacteria apparently break down the connective tissue between muscle fibers, allowing the bacteria to penetrate the meat. Non-proteolytic bacteria do not penetrate meat, even when grown in association with proteolytic species.

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