Evidence of Virulent Multi-Drug Resistant and Biofilm-Forming Listeria Species Isolated from Various Sources in South Africa

Abstract

Listeriosis is a foodborne disease caused by Listeria monocytogenes species and is known to cause severe complications, particularly in pregnant women, young children, the elderly, and immunocompromised individuals. The aim of this study was to investigate the presence of Listeria species in food and water using both biochemical and species-specific PCR analysis. L. monocytogenes isolates were further screened for the presence of various antibiotic resistance, virulence, and biofilm-forming determinants profiles using phenotypic and genotypic assays. A total of 207 samples (composed of meat, milk, vegetables, and water) were collected and analyzed for presence of L. monocytogenes using species specific PCR analysis. Out of 267 presumptive isolates, 53 (19.85%) were confirmed as the Listeria species, and these comprised 26 L. monocytogenes, 3 L. innocua, 2 L. welshimeri, and 1 L. thailandensis. The remaining 21 Listeria species were classified as uncultured Listeria, based on 16SrRNA sequence analysis results. A large proportion (76% to 100%) of the L. monocytogenes were resistant to erythromycin (76%), clindamycin (100%), gentamicin (100%), tetracycline (100%), novobiocin (100%), oxacillin (100%), nalidixic acid (100%), and kanamycin (100%). The isolates revealed various multi-drug resistant (MDR) phenotypes, with E-DA-GM-T-NO-OX-NA-K being the most predominant MDR phenotypes observed in the L. monocytogenes isolates. The virulence genes prfA, hlyA, actA, and plcB were detected in 100%, 68%, 56%, and 20% of the isolates, respectively. In addition, L. monocytogenes isolates were capable of forming strong biofilm at 4 °C (%) after 24 to 72 h incubation periods, moderate for 8% isolates at 48 h and 20% at 72 h (p < 0.05). Moreover, at 25 °C and 37 °C, small proportions of the isolates displayed moderate (8–20%) biofilm formation after 48 and 72 h incubation periods. Biofilm formation genes flaA and luxS were detected in 72% and 56% of the isolates, respectively. These findings suggest that proper hygiene measures must be enforced along the food chain to ensure food safety.

Multidrug-Resistant Biofilms (MDR): Main Mechanisms of Tolerance and Resistance in the Food Supply Chain

“…The authors suggested that the integron migrated to anthropogenic environments through food [80]. MDR pathogens such as Salmonella, methicillin-resistant S. aureus (MRSA), Listeria monocytogenes, Campylobacter jejuni, E. coli O157:H7, and Vancomycin-resistant enterococci (VRE) have been associated with foodborne outbreaks [15,16,118,119]. Furthermore, in the USA these MDR microorganisms are estimated to cause approximately two million illnesses and 23,000 deaths each year [120].…”

“…The results demonstrated a strong relationship between the presence of antibiotic-resistance genes and the ability to build biofilm. Kaptchouang et al [15] evaluated a total of 207 samples (meat, milk, vegetables, and water) and found that L. monocytogenes isolates were resistant to several antibiotics and showed a strong biofilm formation.…”

“…Several outbreaks involving food and MDR microorganisms have been reported in recent years, corroborating the need for greater attention being paid to these pathogens in the food production chain [14][15][16][17]. In 2014, an outbreak involving Salmonella Heidelberg in mechanically separated meat (MSM) from poultry was reported in the USA, in which 67% of the isolates identified were MDR [18,19].…”

Foodborne Pathogen Biofilms: Development, Detection, Control, and Antimicrobial Resistance

“…Strains isolated from food processing environments formed biofilms at a higher frequency than strains isolated from food, and inlB, luxS , and sigB were detected in all strains from food processing environments. Kaptchouang Tchatchouang et al also evaluated the biofilm formation ability and the frequency of biofilm-associated genes ( flaA, luxS ) in L. moncytogenes isolated from South African food samples [ 22 ]. They found that all isolates consistently and strongly formed biofilms at 4 °C for 24, 48, and 72 h. Biofilm-forming genes flaA and luxS were detected in 72% and 56% of the isolates, respectively.…”