Development of a risk-based methodology for estimating survival and growth of enteropathogenic Escherichia coli on iceberg-lettuce exposed at short-term storage in foodservice centers

Ready-to-eat lettuce is a food commodity prone to contamination by pathogenic microorganisms if processing and distribution conditions as well as handling practices are not effective. A challenge testing protocol was applied to ready-to-eat iceberg-lettuce samples by inoculating different initial contamination levels (4.5, 3.5 and 2.5 log cfu/g) of Escherichia coli strain (serotype O158:H23) subsequently stored at 8, 12, 16, 20 and 24 °C for 6 h. A polynomial regression model for log difference (logdiff) was developed at each inoculum level studied through the calculation of the effective static temperature (Teff). Furthermore, the developed model was integrated within a risk-based approach with real time/Temperature (t/T) data collected in three Spanish foodservice centers: school canteens, long-term care facilities (LTCF) and hospitals. Statistical distributions were fitted to t/T data and estimated logdiff values were obtained as model outputs through a Monte Carlo simulation (10,000 iterations). The results obtained at static conditions indicated that the maintenance of the lettuce at 8 °C slightly reduced the E. coli population from − 0.4 to − 0.5 log cfu/g. However, if chill chain is not maintained, E. coli can grow up to 1.1 log cfu/g at temperatures above 16 °C, even at low contamination levels. Regarding logdiff estimated in foodservice centers, very low risk was obtained (logdiff < 1.0 log cfu in all cases). Mean Teff values obtained in hospitals were the lowest ones (11.1 °C) and no growth of E. coli was predicted in > 92% of simulated cases. The results presented in this study could serve food operators to set time/Temperature requirements for ready-to-eat foods in foodservice centers, providing a scientific basis through the use of predictive modeling. These findings may also serve to food safety managers to better define the control measures to be adopted in foodservice centers in order to prevent food-borne infections.

► Survival and growth of E. coli O158:H23 was studied in ready-to-eat iceberg lettuce.
► A significant increase of E. coli population was observed at temperatures above 16 °C.
► A risk-based approach was implemented to account for variability in growth potential of E. coli.
► Low contamination levels of E. coli in iceberg-lettuce increased the percentage of no growth cases.
► Predictive modeling can help to set t/T requirements in foodservice centers during storage, processing and distribution.