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

Aim: 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). Methods and results: The collection was characterized by pulsed-field gel electrophoresis (PFGE). The most prevalent pulse-type was PFGE profile I (n = 14 center dot 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 center dot 4% (n = 77) of the L. monocytogenes collection. The other serovars were as follows: 4b (14 center dot 1%, n = 19), 1/2b (9 center dot 7%, n = 13), 4c (4 center dot 4%, n = 6) and 1/2c (6 center dot 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 center dot 5%). Conclusions: 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. Significance and Impact of Study: 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.