Phenotypic and genotypic characteristics of L. monocytogenes isolates from cockroaches in farm produce market

Objective To understand the carriage of Listeria monocytogenes by cockroaches and whether cockroach is a risk factor for L. monocytogenes caused food contamination in farm produce markets. Methods A survey was conducted in a farm produce market in Beijing from October to December 2015. A total of 147 cockroach samples were collected from the farm produce market selling raw pork, raw mutton, raw chicken meat and aquatic product. The L. monocytogenes isolates were analyzed by serotyping, multi locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Results The positive rate of Listeria in cockroaches, including L. monocytogenes, L. innocua and L. welshimeri, was 58.06% (78/147), and the positive rate of L. monocytogenes was 17.68% (26/147). The detection rate of L.monocytogenes was highest in aquatic product section (18.18%). Serotyping divided 26 isolates into four serotypes, i.e. 1/2c, 1/2a, 3a and 1/2b. Serotype 1/b (34.6%) and 1/2c (34.60%) were predominant. By PFGE, the 26 isolates were classified into 11 PFGE types (PTs), PT16 (19.23%) and PT30 (19.23%) were the major types. By MLST, 5 sequence types (STs) were found (ST87, ST9, ST121, ST155 and ST35) and the major ST was ST87 (34.62%). Conclusion Cockroaches in farm produce markets can carry L. monocytogenes and the genotypic and phenotypic characteristics L. monocytogenes varied with the cockroaches fdifferent sources, which might be due to the different L. monocytogenes in different foods and co-contamination between cockroach and food. Cockroaches is a risk factor for L. monocytogenes spread and contamination in farm produce markets.