Purpose: This study characterized the microbial quality of ready-to-eat produce items in university dining facilities using data collected over twelve years, to determine if a unified microbial quality standard for all fresh produce would be possible. The relationship between indicator organisms and foodborne pathogens was also explored.
Methods: Data were obtained from 955 produce samples taken from university dining facilities. Total aerobic count, presumptive and confirmed total coliform, and fecal coliform counts were determined using FDA BAM methods. Each sample was also tested for the presence of generic E. coli, pathogenic E. coli, Salmonella, Staphylococcus aureus, Listeria monocytogenes and Bacillus cereus. Statistical analysis was performed for any produce items where n>30.
Results: Data from thirteen different produce types met the criteria for inclusion (n>30). Apples had the lowest median total aerobic count (2.8 log CFU/g), while spinach had the highest (6.7 log CFU/g). Apple, cauliflower and mixed lettuce had the lowest median of total coliform counts, while bell peppers had the highest (3.0 log CFU/g). Bell pepper had the lowest median B. cereus counts (1.7 log CFU/g), while spinach had the highest with a median of 2.8 log CFU/g. Staphylococcus aureus was isolated in 2.5% of samples, Escherichia coli from 1.4% of all the samples, and E. coli O157:H7 was isolated only once. Salmonella spp. was isolated from 0.7% of samples, L. monocytogenes from 0.3% of all the samples, and B. cereus from 6.8% of samples.
Significance: Since levels of indicators were highly variable, development of a uniform microbial quality standard is problematic. Because foodborne pathogens were rarely isolated, it was not possible to determine suitable indicators.