This study determined the sources of contamination by Escherichia coli and enterococci in frozen ready-to-eat chicken products. The efficiency of the heat treatment process was sufficient to eliminate E. coli or enterococci. However, the prevalence of E. coli and enterococci in cooked chicken after chilling was 2.7%, and after slicing and dicing it was 1.3 and 9.3%, respectively. These results indicated that contamination occurred after cooking. In the finished product, E. coli was absent, while enterococcus prevalence was reduced to 1.3%. The environment at each production step, such as the machine surfaces, workers' gloves, and the condensate, was sampled to determine the correlation with the contamination in products. E. coli and enterococci were found on the machine surfaces in all production steps, but E. coli contamination was mostly from the infeed transfer belt at the chilling step, while the enterococcus contamination arose mostly from the slicing or dicing steps, especially from the dicing machine belt, which directly contacts the products. Indeed, E. coli and enterococci were detected on food contact surfaces throughout the production period, including prior to its commencement. These results indicated that the cleaning before and during the production process was ineffective. In addition, cleaning and sanitizing food contact surfaces followed by nonfood contact surfaces (floor and drains) by use of a high-pressure water hose created aerosol with microbes from the floors and drains and spread such microbes onto already cleaned food contact surfaces.
Evaluating the efficacy of sodium acid sulfate to reduce Escherichia coli O157:H7 and its biofilms on food-contact surfaces