Contamination patterns and molecular typing of Bacillus cereus in fresh-cut vegetable salad processing

Microbiological contamination of fresh vegetables is a recent food safety concern. Bacillus cereus has been recognized as the most frequently detected foodborne pathogen in fresh-cut salads in Korea. Prevalence and level of contamination of B. cereus was determined in samples from processing lines of packaged fresh-cut vegetable salad manufacturing companies (A, B, C, and D). B. cereus was detected in the 27.3-30.8 % of food samples (raw material, salads in washing steps, and final products) and the contamination levels were up to $9.5{\times}10^2CFU/g$, while detection rates in environmental samples were very low. Molecular subtyping of B. cereus strains detected in the processing environments (company A) and retail products (companies A and E) was conducted to reveal the contamination sources during processing. High genetic similarity was found in the bacterial strains obtained from the processing lines and retail products of company A. This result suggested that B. cereus strains of same clone may have circulated in the products prepared in the same company. Genetic similarities were also observed among part of the B. cereus isolates obtained from the processing line of company A and from the retail products of company E, suggesting that some of the B. cereus clones may have originated from the raw materials. The identified information can be used to develop the intervention technology for fresh-cut vegetable processing.