Coliforms and prevalence of Escherichia coli and foodborne pathogens on minimally processed spinach in two packing plants.

Minimally processed spinach has been recently associated with outbreaks of foodborne illnesses. This study investigated the effect of commercial minimal processing of spinach on the coliform and Escherichia coli counts and the prevalence of E. coli O157:H7, Salmonella, Shigella spp., and Listeria monocytogenes on two types of spinach before and after minimal processing. A total of 1,356 spinach samples (baby spinach, n = 574; savoy spinach, n = 782) were collected daily in two processing plants over a period of 14 months. Raw spinach originated from nine farms in the United States and three farms in Canada. Overall, the proportion of samples positive for coliforms increased from 53% before minimal processing to 79% after minimal processing (P < 0.001). Average total coliform counts also increased significantly after processing, especially in baby spinach (mean +/- standard deviation, 1.16 +/- 0.14 log CFU/g to 2.37 +/- 0.08 log CFU/g following processing; P < 0.001). E. coli was isolated from 8.9% of the samples (mean +/- standard deviation, 1.81 +/- 0.14 log CFU/g), and no difference in prevalence or CFU counts after processing (P > 0.1) was observed. E. coli O157:H7 and Shigella spp. were not isolated from any of the samples. Salmonella and L. monocytogenes were isolated from 0.4 and 0.7% of samples, respectively. Results demonstrate that commercial minimal processing of spinach based on monitored chlorine washing and drying may not decrease microbial load on spinach leaves as expected. Further research is needed to identify the most appropriate measures to control food safety risk under commercial minimal processing of fresh vegetables.