A recall was issued for lettuce that was contaminated with Escherichia coli. If the initial microbial load on the lettuce after packing was 200 CFU/g, how long would it take to reach a microbial load of 100,000 CFU/g? The generation time of E. coli is 20 minutes. Assume ideal conditions, no immigration or emigration. Also, describe one possible way lettuce can be contaminated with E. coli before it reaches the grocery store (i.e., at what point in the production chain can contamination occur and how).
