Antibiotic Resistance Profile of Listeria monocytogenes Recovered from Ready-to-Eat Foods Surveyed in South Africa.

ABSTRACT: In recent decades, there has been an increase in the reports of antimicrobial resistance of Listeria monocytogenes, which constitutes a serious threat to the therapeutic management of listeriosis infection. Our study profiled the antibiogram fingerprint of L. monocytogenes isolates (n = 194) recovered from common South African ready-to-eat foods. L. monocytogenes isolates recovered from foods were tested against a panel of 22 antibiotics using the disk diffusion method. Antimicrobial resistance (>50%) against ceftriaxone (53.1%), trimethoprim (56.2%), streptomycin, cefotetan (59.3%), sulfamethoxazole (61.9%), vancomycin, and oxytetracyclines (62.9%) were observed. Thirty of the isolates (15.5%) were resistant against only one or two antibiotics, whereas 162 (83.5%) exhibited phenotypic multiple antibiotic resistance. Only two (1%) of the isolates did not exhibit phenotypic resistance against any antibiotics screened. Multiple antibiotic phenotypes revealed high resistance patterns, and the multiple antibiotic indices were greater than the Krumperman permissible (>0.2) benchmark. Of the 44 genes screened, 22 antimicrobial resistance genes were detected among ready-to-eat food isolates, including resistance determinants that encode sulfonamides (n = 125, 64.4%), β-lactams (n = 86, 44.3%), phenicols (n = 25, 12.9), and aminoglycosides (n = 93, 47.9%) resistance. We conclude that the presence of resistant L. monocytogenes isolates harboring corresponding antimicrobial resistance genes in foods could compromise safety and constitute severe health consequences if consumed.