Prevalence of Listeria spp. at a poultry processing plant in Brazil and a phage test for rapid confirmation of suspect colonies

Abstract

Sites and occurrence of Listeria contamination in an industrial poultry processing plant were investigated by sampling carcasses at varying stages of processing and testing the hands and gloves of food handlers as well as the chilling water used in the process. In the course of nine visits to a local processing plant we collected a total of 121 samples: 66 from carcasses, 37 from workers' hands and gloves and 18 from the water used for chilling. Except for the water samples Listeria was isolated at all sampling sites. The species most often isolated was Listeria innocua, which accounted for 28 of the 31 (90.3%) isolates. The frequency of Listeria in the chicken carcasses was similar at bleeding, defeathering and end of evisceration stages (33.3%), reduced during scalding (16.7%), and rose immediately after initial evisceration stage (50%) to peak after packaging (76.2%). The carcasses were contaminated by L. monocytogenes serotypes 1b and 1c only during packaging. The prevalence of Listeria spp. on workers' hands and gloves was 46% mostly with L. innocua (40.5%) followed by L. monocytogenes 1b (11.8%). Chilling water presented more than 100 ppm of chlorine, which could explain why the samples were negative to Listeria. As the contamination by Listeria in the carcasses progressively rose both in number, species and strains during processing it seems reasonable to conclude that those carcasses become contaminated at the processing level. Improvement and innovation measures to control bacteria in general at the processing plant level are necessary to effectively reduce final product contamination by L. monocytogenes. In the course of this work we introduced a bacteriophage susceptibility test to confirm suspected Listeria colonies which was able to reduce the time of analysis to a minimum of 30 h depending on the isolation technique employed.