Control of Virulent Listeria monocytogenes Originating from Dairy Products and Cattle Environment Using Marine Algal Extracts, Silver Nanoparticles Thereof, and Quaternary Disinfectants

Introduction: Listeria monocytogenes is an important foodborne pathogen of public- and animal-health concern globally. The persistence of L. monocytogenes in the dairy-processing environment has multifactorial causes, including lack of hygiene, inefficient cleaning, and improper disinfection practices. Materials and Methods: A total of 300 dairy-product and environmental samples were collected from dairy-cattle facilities and local dairy shops and vendors in Qena, Egypt. Samples were screened for the incidence of Listeria spp. and to detect virulence determinants and disinfectant-resistance genes. Three marine algal species — Caulerpa racemosa , Jania rubens , and Padina pavonica — were collected from Hurghada on the Red Sea coast. Algal extracts were screened using gas chromatography–mass spectrometry. The antimicrobial activity of some marine algal extracts, nanoparticles derived therefrom, and some disinfectants against L. monocytogenes strains were assessed in vitro using agar-well diffusion and liquid-broth methods. The impact of P. pavonica extract on the growth and survival of virulent L. monocytogenes in cheese and whey were clarified. Results and Discussion: The incidence of L. monocytogenes in dairy products and environmental samples was 15.5% and 19%, respectively. The most common toxigenic gene profile found among the isolates was hlyA + – inlA + – prfA + . The sensitivity pattern of L. monocytogenes strains to disinfectant containing alkyl (C 12– 16 ) dimethyl BAC was high compared to other tested quaternary ammonium compounds (QAC) disinfectants tested, which showed lower log reductions against resistant strains. The QAC disinfectant–resistance gene qacH was detected in 40% of the isolates. Potent bactericidal activity of a petroleum ether extract of P. pavonica and silver nanoparticles of P. pavonica were obtained against the virulent L. monocytogenes strain. The population of L. monocytogenes in cheese curd and whey after 14 days was reduced at a rate of 9 log CFU/g and 8 log CFU/mL, respectively due to the effect of P. pavonica extract. After 28 days of storage, L. monocytogenes was completely inactivated in those dairy products. Conclusion: P. pavonica extract showed promising antimicrobial properties, calling for further comprehensive studies prior to it being applied in the food industry to enhance the safety, quality, and shelf life of products and protect public health. Keywords: Listeria monocytogenes , virulence genes, cheese, qacH gene, disinfectants, algae, antimicrobial activity