Occurrence and Molecular Characterization of Multidrug-Resistant Vegetable-Borne Listeria monocytogenes Isolates

Zizipho Ntshanka; Temitope C Ekundayo; Erika M du Plessis; Lise Korsten; Anthony I Okoh

doi:10.3390/antibiotics11101353

Occurrence and Molecular Characterization of Multidrug-Resistant Vegetable-Borne Listeria monocytogenes Isolates

Antibiotics (Basel). 2022 Oct 4;11(10):1353. doi: 10.3390/antibiotics11101353.

Authors

Zizipho Ntshanka^{1

2}, Temitope C Ekundayo^{1

2

3}, Erika M du Plessis⁴, Lise Korsten⁴, Anthony I Okoh^{1

2

5}

Affiliations

¹ SAMRC Microbial Water Quality Monitoring Centre, University of Fort Hare, Alice 5700, South Africa.
² Applied and Environmental Microbiology Research Group, Department of Biochemistry and Microbiology, University of Fort Hare, Alice 5700, South Africa.
³ Department of Biological Sciences, University of Medical Sciences, Ondo City PMB 536, Nigeria.
⁴ Department of Plant and Soil Sciences, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa.
⁵ Department of Environmental Health Sciences, College of Health Sciences, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates.

Abstract

Fresh vegetables play a significant role in the human diet. However, ready-to-eat (RTE) vegetables have been associated with increasing foodborne outbreaks including L. monocytogenes, which is a common human pathogen associated with foodborne infections resulting in listeriosis. This study aims to assess the resistance of vegetable-borne L. monocytogenes to antibiotics. L. monocytogenes was isolated and molecularly characterized using polymerase chain reaction (PCR) from 17 RTE vegetable samples. The confirmed L. monocytogenes was further assessed for phenotypic and genotypic antibiotic resistance using the disc diffusion test and PCR primers targeting six antibiotic classes and thirty-one related antibiotic resistance genes (ARGs), respectively. The results revealed that Listeria counts ranged from 1.60 to 3.44 log₁₀ CFU/g in the samples. The isolates exhibited high resistance against penicillin G, erythromycin, vancomycin, tetracycline, trimethoprim-sulfamethoxazole, and nitrofurantoin among the 108 isolates tested. A total of 71 multiple antibiotic resistance (MAR) phenotypes were observed in the isolates, which ranged from resistance to 3 to 13 antibiotics. The MAR index was ˃0.2 in 97% of the isolates. Some of the highly detected ARG subtypes included SulI (100%), TEM (76.9%), tetA (59%), and tetM (54.7%). The findings show a high occurrence of multidrug-resistant L. monocytogenes and clinical ARGs in fresh vegetables, which constitutes an immediate danger for the health security of the public.

Keywords: antibiotic resistance gene; multidrug-resistant; multiple antibiotic resistance (MAR) index; public health; risk; vegetable.

Grants and funding

We are grateful to the South African Medical Research Council, the United States Agency for International Development and the Department of Science and Technology of South Africa for financial support.