Profiling Listeria monocytogenes in Hummus, Fresh Produce, and Food Processing Environments in the Western Cape, South Africa

Abstract

Listeria monocytogenes is pervasive in agricultural environments and difficult to eradicate from food-processing facilities. Consequently, various foods become contaminated, posing health risks to immunocompromised individuals. This surveillance study aimed to enhance the understanding of the genetic diversity, virulence, plasmid content, sanitizer tolerance, and antibiotic resistance of L. monocytogenes from ready-to-eat (RTE) hummus, fresh produce and food-processing environments in the Western Cape, South Africa (2018–2021). Sixty L. monocytogenes isolates were classified as lineage I or lineage II using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Lineage I was notably prevalent overall (57%; n = 34) and significantly associated with fresh produce (88%; n = 7) (p = 0.04). Whole-genome sequencing (WGS) and bioinformatic analysis characterized a subset of 20 L. monocytogenes isolates into seven sequence types (STs) (ST1, ST2, ST3, ST5, ST101, ST121, ST204), and three serotypes (1/2a, 1/2b, 4b). ST204 (38%; n = 3) was most prevalent in the food-processing environment, ST5 (50%; n = 3) in fresh produce, and ST5 (33%; n = 2), ST101 (33%; n = 2) and ST121 (33%; n = 2), in RTE hummus. However, no single serotype or ST was significantly overrepresented in any category (p > 0.05). All isolates carried both Listeria pathogenicity island (LIPI)-1 and LIPI-2 gene clusters. Two isolates (ST1 and ST3) contained all genes comprising LIPI-3. Two ST5 isolates from RTE hummus contained the tetM gene. Isolates from different origins contained the emrC, bcrABC or qacH genes conferring tolerance to benzalkonium chloride, a quaternary ammonium compound class of sanitizer. RTE hummus, fresh produce and the food-processing environment are susceptible to contamination by diverse and virulent L. monocytogenes strains.