Prevalence, virulence potential, antibiotic resistance profile, heavy metal resistance genes of Listeria innocua: A first study in consumed foods for assessment of human health risk in Northern Turkey

Listeria (L.) innocua is typically considered a non-pathogenic bacterium that can sometimes act as an opportunistic pathogen in severely immunocompromised patients. However, it plays an important role in food safety because it acts as an indicator organism for potential contamination and the effectiveness of sanitation methods. The aim of this study was to determine the prevalence, virulence genes, antibiotic resistance profiles, heavy metal and disinfectant resistance genes of L. innocua isolates from animal-derived foods. In this study, we isolated and characterized 39 L. innocua strains recovered from commonly 400 consumed beef meat, fresh fish meat, raw cow milk, and traditional cheese samples collected in Giresun, Turkey. The occurrence of virulence-associated genes was detected, such as plcA (97.4%), iap (35.8%), and hlyA (15.3%). A high incidence of resistance was recorded for fusidic acid (100%), followed by oxacillin (97.4%), clindamycin (82%), trimethoprim/sulfamethoxazole (69.2%), benzylpenicillin (41%), nitrofurantoin (35.8%), and fosfomycin (35.8%). Overall, 100% (39/39) of the isolates were resistant to at least one antibiotic, while 92.3% (36/39) of the isolate strains were multidrug resistant in the antimicrobial susceptibility tested. Among the L. innocua isolates (n = 39), 51.2%, 38.4%, 20.5%, 7.6%, 5.1%, 2.5%, and 2.5% were positive for qacH, cadA1, qacE, qacEΔ1-sul, qacJ, qacF, and qacG heavy metal and disinfectant resistance genes, respectively. The results highlight the need for more comprehensive studies to understand the monitoring and surveillance of L. innocua and their potential hazards to both humans and animals.