Escherichia coli contamination of lettuce (Lactuca sativa) sold in Trinidad and Tobago

Abstract

The increasing consumption of fresh produce as part of a healthy diet has been mirrored by an increasing incidence of foodborne disease outbreaks. Contamination of fresh vegetable produce with foodborne pathogens is of particular concern since these products undergo minimal processing or are consumed raw. In addition to being a potential source of foodborne pathogens, antimicrobial resistant bacteria can be easily transmitted to humans when they consume or come in contact with contaminated vegetable produce. Using Escherichia coli as an indicator of faecal contamination, we evaluated lettuce (Lactuca sativa) as a potential source of foodborne disease and antimicrobial resistant bacteria. A cross-sectional study was carried out targeting six retail vegetable markets (A-F), and the E. coli counts (CFU/g lettuce) were assessed using standard laboratory techniques. Recovered E. coli isolates were then subjected to antimicrobial sensitivity testing to the four primary antibiotics used in livestock production in Trinidad and Tobago. Overall, the E. coli counts ranged from 0.8 to 800,000 CFU/gram of lettuce, with approximately 55% of samples exceeding 100 CFU/gram (2 log 10 CFU/g). The E. coli counts varied with market location (P <= 0.001), with the highest average count being at market E (3.41 log 10 CFU/g), and the lowest at location D (1.47 log 10 CFU/g). Approximately, 22% of the E. coli isolates screened (4/18) exhibited resistance to amoxicillin-clavulanic acid, while 11% (2/18) exhibited resistance to tetracycline. None of the isolates exhibited resistance to more than one antibiotic type. These high E. coli counts are indicative of either preharvest or postharvest faecal contamination of lettuce. These results demonstrate that lettuce can potentially serve as a vehicle for the dissemination of both foodborne pathogens and antimicrobial resistant organisms.