Occurrence and antimicrobial susceptibility of Listeria monocytogenes isolates from retail raw foods

The occurrence and counts of Listeria monocytogenes were investigated in a total of 526 retail raw food samples. All L monocytogenes isolates were further analyzed by serotyping and antimicrobial susceptibility assays. The molecular basis of tetracycline resistance of each isolate and the genetic relatedness were determined. L monocytogenes isolates were found in 12.4% (65/526) Of the samples, with counts below 10(2) CFU/g. L. monogtogenes was most commonly isolated from pork (20%, 20/100), seafood (13.8%, 15/109), chicken (13.2%, 14/106), and beef (103%, 11/107). In addition, L monocytogenes was also detected in 4.8% (5/104) of raw mutton samples. Four serogroups were identified among the 65 L. monocytogenes isolates, with serogroups 1/2a-3a (60%) and 4b-4d-4e (24.6%) being dominant. Most L. monocytogenes isolates were resistant to cefotaxime (54.6%), fosfomycin (51.5%), and clarithromycin (36.4%). Some isolates showed intermediate resistance to streptomycin (12.1%), norfloxacin (13.6%), ciprofloxacin (13.6%), and nitrofurantoin (9.1%). Multiple resistances were observed in 72.3% of isolates. Genetic relatedness analysis revealed that there were no prominent associations between specific food types, serotypes, antimicrobial susceptibility profiles and Pulsed-field gel electrophoresis (PFGE) patterns. In addition, these isolates were multiresistant and belonged to the epidemiologically important serotypes 1/2a and 4b, implying a potential public health risk. (C) 2012 Elsevier Ltd. All rights reserved.