The characterization of Listeria spp. isolated from food products and the food-processing environment

Abstract

To enhance the information pertaining to the epidemiology of a collection of 378 Listeria spp. isolates obtained from several food-processing plants in Ireland over a 3-year period (2004-2007). The collection was characterized by pulsed-field gel electrophoresis (PFGE). The most prevalent pulse-type was PFGE profile I (n=14·5%) that consisted mainly of environmental Listeria spp. samples. Serotyping of 145 Listeria monocytogenes isolates was performed. The most common serovar was 1/2a and comprised 57·4% (n=77) of the L. monocytogenes collection. The other serovars were as follows: 4b (14·1%, n=19), 1/2b (9·7%, n=13), 4c (4·4%, n=6) and 1/2c (6·7%, n=9), respectively. Eleven isolates were identified as non-Listeria spp., the remaining ten L. monocytogenes isolates were nontypeable. The antimicrobial susceptibility testing revealed the antibiotic that isolates displayed the most resistance to was gentamicin (5%) followed by sulfamethoxazole-trimethoprim (2%), tetracycline and ciprofloxacin (1·5%). The subtyping has indicated the diversity of the Listeria spp. The presence of serotype 1/2a, 1/2b and 4b in both raw and cooked ready-to-eat food products is a public health concern, as these serotypes are frequently associated with foodborne outbreaks and sporadic cases of human listeriosis. In addition, the emergence of antimicrobial-resistant L. monocytogenes isolates could have serious therapeutic consequences. The molecular subtyping and the further characterization of these isolates may be valuable particularly in the context of a suspected common source outbreak in the future.