Microbiological quality of raw and cooked foods in middle and high school food service establishments

Abstract

The evaluation of microbiological quality for school food samples collected from 19 selected middle and high schools located in Seoul was undertaken. Eighty-nine food samples consisting of 38 non-pretreated vegetables, 13 pre-washed and cut vegetables, 9 meats and poultry, 3 fish and shellfish, 7 dried fish, and shellfish and 20 processed foods were collected. Aerobic plate count, total coliforms, and Escherichia coli (E. coli) were detected using Petrifilm™, and the food-borne pathogens were screened by multiplex PCR with species-specific primer sets. Sequentially, the quantitative and confirmative test of the food-borne pathogens were carried out with the selective media and biochemical kits. The contamination of coliform counts was observed on the pre-washed vegetables (3.4-4.3 log CFU/g) and meats (2.2-4.3 log CFU/ g). Also, the cooked foods were heavily contaminated with coliform, ranging from 1.0 to 5.5 log CFU/g. E. coli counts were found in 16 raw and cooked food samples, exceeding the microbiological standards for the guideline of safety management for school foods. Through PCR detection, Bacillus cereus was detected in 32 raw and cooked foods, and quantitatively found in pre-washed carrot, radish, and pan-broiled dried shrimp and filefish ranging from 2.3-3.6 log CFU/g, respectively. E. coli O157:H7 was detected on frozen pork sample and was confirmed with API kit. Campylobacter jejuni was found in 3 ready-to-eat type vegetables. Vibrio parahaemolyticus were found in 4 pre-washed vegetables and 2 cooked foods, indicating unsatisfactory quality based upon the microbiological standards of ready-to-eat vegetables and cooked foods by Korea Food and Drug Administration. Salmonella spp. was detected in frozen chicken sample and confirmed by API kit and latex antisera agglutination.