Prevalence, molecular profile and antibiotic resistance of Listeria species in retail beef products in North-West Province, South Africa : a cross-sectional analysis

Abstract

This cross-sectional study determined the occurrence, distribution, molecular characteristics and antibiograms of Listeria species recovered from beef and beef products retailed in the North-West Province, South Africa. The study also investigated the factors associated with the contamination of these products by Listeria spp. and their characteristics. Conventional methods and polymerase chain reaction (PCR) were employed to detect and characterize the isolates of Listeria spp. In contrast, the disc diffusion method was used to determine their susceptibility to 16 antimicrobial agents. Four hundred beef products were randomly collected from 30 retail outlets across the North-West Province. The prevalence of Listeria monocytogenes and other Listeria spp. was 6% (24/400) and 30.5% (122/400), respectively (p < 0.001). Of the five variables (district, size of outlet, type of beef and beef products, product display temperature and types of presentation), only the type of beef and beef products had a statistically significant (p = 0.034) effect on the occurrence of L. monocytogenes. In contrast, none had any significant effect on other Listeria spp. Among the 24 isolates of L. monocytogenes, all five serogroups assayed were detected, with the predominant ones being IIb (45.8%), IVb (20.8%) and IIa (20.8%). All eight virulence genes assayed were detected, with actA (50%), inlB (45.8%) and inlA (41.7%) being the most frequently detected. All isolates of L. monocytogenes (n = 24) and other Listeria spp. (n = 122) were resistant to one or more of the 16 antimicrobial agents tested. For L. monocytogenes isolates, resistance was high to nalidixic acid (100%), enrofloxacin (41.7%) and cefoxitin (37.5%) but low to clindamycin (8.3%) and sulphamethoxazole-trimethoprim (8.3%). The frequency of multi-drug resistance (MDR) in the L. monocytogenes isolates was 95.8% (23/24). Our study reveals the risk of human listeriosis in consumers of beef and beef products contaminated by virulent and antimicrobial-resistant serogroups of L. monocytogenes in the North-West Province of South Africa.