Prevalence of Listeria spp. and Molecular Characterization of Listeria monocytogenes Isolates from Broilers at the Abattoir.

Products from three broiler abattoirs were sampled for Listeria species to evaluate the changes in the prevalence and contamination rates at two stages of processing. Sampling was performed at the evisceration stage and at the end of processing after packaging and refrigerating at 4°C for 24 h. A total of 212 samples were collected; 52 were from abattoir A, and 80 samples each were collected from abattoirs B and C. Among all samples, 99 (46.7%) tested positive for Listeria, including L. monocytogenes 19 (8.9%), L. innocua 69 (32.5%), L. grayi 10 (4.7%), and L. welshimeri 1 (0.5%). The L. monocytogenes contamination rate varied from 5% to 11.5% in the 3 abattoirs. L. innocua was the most common species identified and was found in 8.8% of the samples from abattoir A and 33.7% of the samples from both abattoirs B and C. Twenty-six of the L. monocytogenes isolates obtained from positive samples were subjected to serotyping by multiplex polymerase chain reaction and characterization by the pulsed-field gel electrophoresis (PFGE) method using two cutting enzymes, ApaI and AscI. Three molecular serogroups were identified: IIa, IIb, and IVb. Serogroup IIa was common to all abattoirs, and serogroups IIb and IVb were found only in abattoir C. The 10 different obtained PFGE profiles were grouped into 7 clusters; some of these clusters were common to the 3 abattoirs, and others were specific to the abattoirs in which they were identified. This study revealed a high prevalence of Listeria spp., particularly L. monocytogenes, in raw broilers. This high incidence presents a risk to consumers due to the potential occurrence of cross-contamination with other foods in domestic refrigerators and the ability of these microorganisms to survive in undercooked products.