Prevalence, antibiotic resistance and genetic diversity of Listeria monocytogenes isolated from ducks, their rearing and processing environments in Penang, Malaysia

The objectives of this study were to determine the prevalence, antibiotic resistance and genetic diversity of Listeria monocytogenes isolated from ducks and their environmental samples. From August 2009 to October 2010, a total of 531 samples from ducks and their environments were obtained from wet market and commercial duck farms in Penang, Malaysia. Using the conventional bacteriological method and confirmation by phenotypic test strips, 15 samples (2.8%) were positive for L. monocytogenes. Other Listeria spp. identified were Listeria ivanovii (3.6%), Listeria innocua (0.8%), Listeria seeligeri (0.6%), Listeria welshimeri (0.2%), and unknown Listeria spp. (0.9%). The identity of the 15 isolates of L. monocytogenes was confirmed by PCR. The L. monocytogenes isolated also harboured the virulence-associated gene, hlyA. Plasmid DNA size ranged from 2.8 to 21.4 kb. All isolates were susceptible to ampicillin, cephalothin, chloramphenicol, ciprofloxacin, gentamicin and streptomycin but resistant to nalidixic acid. L. monocytogenes strains were grouped into 5 clusters and 3 singletons, 3 clusters and 3 singletons, and 2 clusters and 3 singletons by RAPD, REP, and ERIC respectively, at coefficient of 0.85. Our study indicates that ducks and their environments are contaminated by L. monocytogenes and other Listeria spp. We also describe for the first time the prevalence, antibiotic resistance and the genetic diversity of L. monocytogenes in ducks and duck environmental sources in Malaysia.

► The first detailed study on the prevalence of L. monocytogenes in Malaysian ducks.
► 15 (2.8%) samples were positive for L. monocytogenes.
► MAR index for L. monocytogenes was low.
► All L. monocytogenes isolates harboured the hlyA gene.
► RAPD, ERIC and REP analyses revealed some diversity among L. monocytogenes isolates.