Survival and death of Listeria monocytogenes on cooked bacon at three storage temperatures

Survival of Listeria monocytogenes on cooked bacon cubes (a(w) 0.910 +/- 0.080), strips (a(w) 0.726 +/- 0.054), and bits (a(w) 0.620 +/- 0.038) was determined during a 25 week storage period at -20, 4.4, and 22 degrees C. Selective enrichment and subsequent enzyme-linked fluorescent antibody (ELFA) detection were used to asses survival on samples inoculated at ca. 1-log(10) CFU/g (LI). Samples inoculated at ca. 5.5-log(10) CFU/g (HI) were analyzed over time by direct plating on modified Oxford medium (MOX). The Baranyi model was fitted to the inactivation curves of HI samples using the DMFit program. At -20 degrees C, a decline of about 1-log(10) CFU/g occurred on all HI cooked bacon types by 14 weeks, although most LI samples remained positive by the ELFA detection method for 25 weeks. At 4.4 and 22 degrees C, some strips and bits LI samples were negative for the pathogen within 3 weeks, and >1.5 log(10) CFU/g reductions occurred on HI strips and bits by 8 weeks. Reductions on cubes at refrigeration and ambient temperature were ca. 0.5 log(10) CFU/g, and cubes remained positive on LI samples for 25 weeks. Rate parameter estimates indicated that the population declined fastest on strips and bits at 22 degrees C compared to all other product and temperature combinations. This study demonstrates that cooked bacon does not support the growth of L. monocytogenes and that the pathogen gradually dies off during storage.