Occurrence, antimicrobial resistance pattern and molecular characterization of Listeria monocytogenes isolated from bovines milk and meat in Mekelle City, Ethiopia

Listeria monocytogenes is an opportunistic and emerging foodborne zoonotic pathogen that encompasses a diversity of strains with varied virulence and can cause serious human and animal infections worldwide with low incidence but high hospitalization and case fatality rates. A cross-sectional study was conducted from December 2016 to June 2017 to estimate the molecular epidemiology of L. monocytogenes and its serotypes, and antimicrobial resistance pattern of isolates in Mekelle City. A total of 768 (384 of milk and 384 meat) samples of bovine origin were collected using a purposive random sampling technique. Isolation and identification of L. monocytogenes was done according to standard and recommended bacteriological procedures. Genome-based confirmation of each isolate was performed at species and serovar levels by targeting Iap, Imo0737, ORF2819 and ORF2110 genes using specific primers. In vitro antimicrobial susceptibility testing was performed using agar plate antibiotic disk diffusion method. The overall prevalence of L. monocytogenes was 26 (3.39%). Sample type prevalence rates of L. monocytogenes were 4.17 % and 2.6% in meat and milk samples, respectively. There was a statically significant difference (p<0.05) on the prevalence rates of the organism in meat samples collected from abattoir (1.67%), butcher shops (8.33%), and restaurants (8.33%). Serovars that were identified were belonged to 1/2b and 4b. Large proportions of isolates were highly susceptible to Ampicillin (88.46%) and Vancomycin (84.62%). However, the isolates had shown the highest level of resistance against Nalidixic Acid (96.15%). The highest intermediate was observed to Amoxicillin (57.69%). Moreover, 42.31% of the isolates were developed resistance for more than two drugs. Hence, both its occurrence and development of a multi-drug resistance indicated that, a coordinated effort is imperative to reduce or eliminate the risk posed by this pathogen in food chains and on controlled and careful use of antimicrobials both in veterinary and human treatment regimes.