Listeria monocytogenes and Other Species as Persistent Contaminants in the Processing of Chicken Meat

To determine the occurrence of Listeria monocytogenes (LM) and other species in different stages of the processing of broiler chickens, comparing a real-time PCR protocol with standard morphological and biochemical proofs as confirmatory tests for LM, 100 samples from 5 monitoring points (carcass after evisceration, carcass after chilling, packaged frozen carcass, knives and boards of the cutting room, and packaged frozen boneless thighs) were obtained throughout a 3-mo evaluation period in an export-authorized industrial facility in Brazil. Data were analyzed using the non-parametric Wilcoxon test and, in case of difference, means were contrasted with control (carcass after evisceration) by the Dunn test (P < 0.05). Carcasses were negative for Listeria sp. immediately after evisceration, but LM was confirmed in both chicken meat and chicken-meat processing environment after that point (maximum 30% occurrence). Listeria innocua, L. grayi, and L. welshimeri were also isolated from samples. Comparing LM confirmatory tests, real-time PCR performed better than the morphological and biochemical assays in samples from packaged frozen boneless thighs. In fact, all the isolates obtained from frozen products behaved negative in the hemolysis tests, leading to some false-negative results in the morphological and biochemical confirmation. The detection limit of real-time PCR for LM was 1.34 CFU. Overall, the results of this study indicate the inefficacy of the cleaning and disinfection program adopted by the industry to control LM. Also, to avoid false-negative results, our recommendation is that real-time PCR can be used in combination with standard microbiological methods in the confirmatory analysis of LM, especially when frozen products are under consideration.