Isolation, phenotypic characterization and public health implications of Listeria monocytogenes circulating in smallholder dairy farms of Kombolcha town and Kutaber district, Amhara regional state, Ethiopia

Abstract

Background: Listeria monocytogenes is a bacterium of veterinary and public health importance, worldwide. The pathogen is among the major causes of abortion in dairy cattle. Listeriosis in humans is the main food-borne zoonotic illness resulted from consuming dairy and other food products contaminated with mainly Listeria monocytogenes. A cross-sectional study was conducted from November 2020 to May 2021 to isolate Listeria monocytogenes from raw bovine milk samples, to determine the Antibiogram of isolates and to understand its public health implication in smallholder dairy farms. Listeria species isolation was performed, according to standard bacteriological procedures, using Buffered Listeria Enrichment broth (BLEB) and Polymyxin Acriflavine Lithium-chloride Ceftazidime Aesculin Mannitol (PALCAM) agar and for confirmation and species identification: carbohydrates utilization tests using xylose, mannitol and rhamnose sugars, hemolysis test using blood agar, Christie Atkins Munch Peterson (CAMP) test and Listeriolysin 0 latex agglutination test was carried out. The antimicrobial susceptibility test using 9 commonly used antimicrobial drugs against 15 Listeria monocytogenes isolates, and a questionnaire survey were also conducted. Results: From the total of 384 samples the overall prevalence of Listeria species was 12.8% (49/384) and specifically for Listeria monocytogenes was 4% (15/384). In this study, listeriosis is significantly associated with farm management systems and herd size (p-value< 0.05). Based on the antimicrobial susceptibility test, it was found that Listeria monocytogenes was sensitive to most drugs except Sulfamethoxazole and nalidixic acid which in both showed 100% resistance. 13.3% of L. monocytogenes isolates were also resistant to oxytetracycline, tetracycline, procaine penicillin G and cloxacillin. Conclusion: This presence of Listeria monocytogenes in raw milk and its multi-drug resistance pattern is an indication of a serious public health risk. Therefore, creating awareness to the farmers, and dairy product consumers, implementation of milk safety hygienic practices, implementation of countrywide surveillance and further research to estimate its prevalence both in animals and humans is strongly recommended.