Occurrence, Numbers, and Growth of Listeria monocytogenes on some Vacuum-Packaged Processed Meats

Listeriae were detected on 93 of 175 samples of vacuum-packed processed meats obtained from retail stores. More than 1000 colony forming units of listeriae per g were found on seven of 130 samples in which the numbers of listeriae were estimated. When sliced corned-beef and ham, from four manufacturers, were inoculated with Listeria monocytogenes and vacuum-packed, the growth rate of the organism varied with the composition of the product. High residual nitrite or lowered a_w reduced growth, particularly when products were stored at 0 to 5°C. As the storage temperature increased from 0 to 15°C, the growth rate of L. monocytogenes increased more rapidly than that of the other flora (lactic acid bacteria and Brochothrix thermosphacta ). Growth rates on inoculated packs were similar to rates observed for packs contaminated with L. monocytogenes during commercial production.