Occurrence, serotypes, and characteristics of Listeria monocytogenes in meat and meat products in South Africa between 2014 and 2016

Listeria monocytogenes is an intracellular pathogen that causes life-threatening disease called listeriosis. However, in South Africa (SA), there is a dearth of information concerning the potential role of meat and meat products as potential sources for human listeriosis. The aim of the study was to determine the occurrence and level of L. monocytogenes found in meat and meat products in SA and to characterize L. monocytogenes strains according to serogroups, antimicrobial resistance profiles and virulence genes. A total of 2,017 samples from imported and locally produced raw, processed and ready to eat meat were collected from 2014 to 2016 across nine provinces of SA. The samples for L. monocytogenes were isolated using microbiological techniques and real-time polymerase chain reaction (PCR). Antimicrobial resistance profiles of the isolates were determined by testing 19 antimicrobial impregnated discs using Kirby-Bauer disc diffusion method. Characterization in terms of serogroup typing and virulence profiling was done using conventional PCR. The overall occurrence of L. monocytogenes was 14.7% (296/2,017), which varied between meat collected on the domestic market (15.0%; 264/1,758) and directly at the three ports of entries (12.4%; 32/259). The contamination level of the positive samples ranged from 1 to 3.7 log CFU/g and 1 to 4.1 log CFU/g for samples collected from the domestic and imported meat, respectively. All positive isolates were serotyped by multiplex PCR, of which majority of the isolates belonged to molecular serogroup 1/2a-3a (45.5%), followed by 4b-4d-4e (24.2%), and 1/2c-3c (15.2%). Most of the isolates harbored the inlJ (98.7%) and ipa (95.6%) genes. However, at least one of the other internalin genes (inlB, inlC, and inlA) was present in most of the isolates. All the tested isolates showed resistance to at least 3 of the 19 antibiotics, with 5 (1.7%) of them displaying resistance to 13 of the 19 antibiotics. Resistance to streptomycin (99.0%), clindamycin (97.3%), fusidic acids (95.6%), nitrofurantoin (79.7%), and gentamycin (74.4%) was observed while high rates of sensitivity were observed for ampicillin (85.6%), kanamycin (84.6%), amikacin (77.6%), vancomycin (74.2%), and tetracycline (62.5%). The presence of L. monocytogenes in various meat products in SA pose a risk to human health. Therefore, the present research provides valuable baseline information that will help in the development of policies and regulations for monitoring of L. monocytogenes in meat and meat products in SA. Practical applications This study is extensive and involved analysis of meat and meat products from all the nine provinces of South Africa. Furthermore, the study involved analysis of imported meat (from the three major ports of entry) that was destined for the South African market. The findings that were obtained are significant from academic, policy, and practical points of view. The findings provide empirical evidence of the contamination of a proportion of raw intact, raw processed, and ready-to-eat meat and products that are available on the South African market. Furthermore, our findings illustrate the levels of contamination, which is important for providing guidelines with respect to L. monocytogenes contamination of meats. Information of the predominant L. monocytogenes serotypes from this study provide important epidemiological data of the strains that are circulating in meat and meat products. The antimicrobial resistance results are important for contributing to guidelines on antimicrobial use.