Developing a BAM Selective Enrichment Based Enumeration Method for Listeria Monocytogenes in Fresh Produce
T.K. DeValroger2, A.I. Yansaneh2, F.U. Ibebuchi2, R.E. Duvall1 and A.D. Hitchins1,
1FDA, CFSAN, Washington, DC 20204, 2University of Maryland, College Park, MD 20742
Risk assessment of foodborne listeriosis is constrained by sparse quantitative contamination data for Listeria monocytogenes (Lmo). Enumerating contamination is typically done, if at all, only when foods screen positive for listeria by selective enrichment. A hybrid version of these two steps was tested. Low numbers of Lmo were selectively enriched (24 h at 30°C) and the proliferated cells were enumerated by colony counts. The initial contamination level was calculated using an empirically derived mean growth rate. The back calculated and known initial numbers corresponded well with some kinds of sample matrices. An empirical correction was necessary for other matrices, such as fresh produce, where inhibition due to plant microbiota or constituents seems to occur. In practice, an isolates growth parameter will not known, so the mean growth rate was estimated for foodborne strains in general.