Contamination of beef and beef products by Listeria spp. and molecular characterization of L. monocytogenes in Mpumalanga, South Africa

This study determined the prevalence, risk factors, and molecular characteristics of Listeria species detected in beef and beef products sampled in Mpumalanga province, South Africa. Four hundred beef and beef products were collected from 30 retail outlets in three districts (Bronkhorstspruit, Emalahleni, and Middelburg) within the province. Standard bacteriological and polymerase chain reaction (PCR) assays were used in the study. The overall prevalence of L. monocytogenes and other Listeria spp. in the samples was 8.3% (33/400) and 30% (120/400) (p < .05), respectively. For the five variables investigated, statistically significant effects were evident only for the region (p < .001) and type of product (p < .0001) for L. monocytogenes, the type of outlet (p = .011) and the type of product (p < .0001) for Listeria spp. Of the 20 types of beef and beef products tested, 15 (75%) and 17 (85%) were contaminated by L. monocytogenes and Listeria spp., respectively (p = .429). Among the four categories of products tested, the prevalence of L. monocytogenes was 7.3% (8/109), 10.6% (11/104), 7.5% (8/106), and 7.4% (6/81) for raw beef, ready-to-eat (RTE) products, milled beef, and offal & organs, respectively (p > .799). Among the 33 L. monocytogenes isolates, PCR genoserogroup IIa (42.4%, 1/2a-3a) was most frequently detected. All (100%) of the isolates carried one or more of the eight virulence-associated genes assessed, with genes inlC and inlJ detected in all the isolates. The overall prevalence of L. monocytogenes (8.3%) and the high frequency of virulent serogroups of L. monocytogenes commonly associated with human listeriosis pose a food safety risk to consumers of beef and beef-based products contaminated by L. monocytogenes.