Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2010
Publication Date: 3/1/2011
Citation: Hwang, C., Sheen, S. 2011. Growth characteristics of Listeria monocytogenes as affected by a -native microflora in cooked ham under refrigerated and temperature abuse conditions. Food Microbiology. 28:350-355. Interpretive Summary: Outbreaks of food-borne illnesses have been linked to the consumption of refrigerated ready-to-eat (RTE) meat products contaminated with Listeria monocytogenes. This study examined the growth of L. monocytogenes in a RTE ham as affected by a native microflora (non-harmful bacteria naturally found in food) at refrigeration (4 degrees centigrade) and abuse (6-12 degrees centigrade) temperatures. A five-strain mixture of L. monocytogenes and a native microflora isolated from ham were inoculated alone or co-inoculated onto cooked ham slices. The times required for the pathogen and the native microflora to grow (time to growth), their growth rates, and their maximum cell numbers in ham stored at 4, 6, 8, 10, and 12 degrees centigrade were determined. At 4-12 degrees centigrade, the times to growth of L. monocytogenes were not influenced by the presence of the native microflora. At 4-8 degrees centigrade, the growth rates and maximum cell numbers of L. monocytogenes were reduced by the presence of the native microflora. Results indicated that the growth of L. monocytogenes in ham at lower storage temperatures was reduced by the presence of native microflora. Findings from this study add to the understanding of the growth behavior of L. monocytogenes in RTE meats, and can be used to design processing and handling conditions for RTE meat products that reduce the growth probability of L. monocytogenes in these products.
Technical Abstract: This study examined the growth characteristics of L. monocytogenes as affected by a native microflora in cooked ham at refrigerated and abuse temperatures. A five-strain mixture of L. monocytogenes and a native microflora isolated from cooked meat were inoculated alone (monocultured) or co-inoculated (co-cultured) onto cooked ham slices. The growth characteristics, lag phase duration (LPD, h), growth rate (GR, log cfu/h), and maximum population density (MPD, log cfu/g), of L. monocytogenes and the native microflora in the vacuum-packed ham slices stored at 4, 6, 8, 10, and 12 degrees centigrade were determined. At 4-12 degrees centigrade, the LPD of co-cultured L. monocytogenes were not significantly different from those of monocultured L. monocytogenes in ham, indicating the LPD of L. monocytogenes at 4-12 degrees centigrade were not influenced by the presence of the native microflora. At 4-8 degrees centigrade, the GR of co-cultured L. monocytogenes (0.0114-0.0130 log cfu/h) were significantly lower than monocultured L. monocytogenes (0.0132-0.0145 log cfu/h), indicating the GR of L. monocytogenes at 4-8 degrees centigrade was reduced by the presence of the native microflora. The GR of L. monocytogenes were reduced by 8-7% at the presence of the native microflora at 4-8 degrees centigrade, whereas the influence of native microflora on the GR of L. monocytogenes diminished at 10 and 12 degrees centigrade. The MPD of L. monocytogenes at 4-8 degrees centigrade were also reduced by the presence of the native microflora. The native microflora was identified to be Brochothrix spp. Data from this study provide additional information regarding the growth suppression of L. monocytogenes by the native microflora for assessing the survival and growth of L. monocytogenes in RTE meat.