Molecular characterization and antimicrobial susceptibility of Listeria monocytogenes isolated from foods and humans

A total of 120 Listeria monocytogenes isolates (107 from foods and 13 from humans) in Shanghai, China, were characterized by serogroup typing and virulence genes detection with PCR, antimicrobial susceptibility testing, and molecular subtyping using pulsed-field Gel Electrophoresis (PFGE). Isolates belonged to three L. monocytogenes serogroups, l/2c, 3c (n = 47, 39.1%) was the most prevalent, followed by 1/2a, 3a (n = 44, 36.7%) and 1/2b, 3b, 7 (n = 29, 24.2%). Although the isolates were all susceptible to most antibiotics tested, 13 isolates were resistant to ceftriaxone and seven to tetracycline. None of the isolates were resistant to multiple antibiotics. The Yet (M) genes were detected among tetracycline-resistant isolates. The isolates all harbored virulence genes hly, prfA, pIcA, plcB, inlA, inlB, MU; 116 isolates (96.7%) were positive for in1C; 78 (65.0%) for inlG; 119 (99.2%) for in1J; 8 (6.67%) for ilsX. A total of 74 distinct patterns were generated for the 119 isolates tested using Apal and AscI with Pulsed Field Gel Electrophoresis (PFGE). Three clinical isolates shared the same PFGE patterns with retail meet (chicken, duck, and beef) isolates. These findings indicated that food of animal origin likely serve as a major vehicle in transmitting human listeriosis in Shanghai. Active surveillance for L monocytogenes is needed for better understanding the epidemiology of the pathogen, and for effective control and prevention of human listeriosis. (C) 2016 Elsevier Ltd. All rights reserved.