Incidence rates of resistant enterotoxigenic Escherichia coli in fresh vegetables and salads.

Diarrhoeal diseases remain a significant global health challenge, particularly in developing regions such as Africa, Asia and Latin America, where they are a leading cause of child mortality. Contaminated food, including raw or undercooked vegetables, is a major transmission route for diarrhoeal pathogens such as norovirus, Campylobacter, non-typhoid Salmonella and pathogenic Escherichia coli. This study aimed to assess the prevalence of enterotoxigenic E. coli (ETEC), a key diarrhoeal pathogen, in fresh produce and prepared salads in Mexico City. A total of 128 samples, including prepared salads (lettuce, carrots and tomatoes) and unprocessed coriander and lettuce, were analysed over 2 years using protocols from the Bacteriological Analytical Manual and the Official Mexican Standard (NOM) SSA 210. Genotyping was performed to detect ETEC-specific virulence genes encoding heat-stable and heat-labile enterotoxins (st and lt), respectively. ETEC was identified in 9.9% of the total samples, representing 51.56% of the confirmed E. coli isolates. Contamination rates varied by food type, with coriander showing the highest prevalence (78.78%), followed by lettuce (9.09%) and prepared salads from La Vicentina Market (9.09%) and La Purísima Market (3.03%). Genotyping revealed that 12.12% of the ETEC-positive samples carried both st and lt genes, while 33.3 and 54.6% carried only the lt or st gene, respectively. In lettuce samples, 9.09% were positive for ETEC, with 3.03% carrying the lt gene, 3.03% the st gene and 3.03% both genes. Similarly, in coriander, 21.21% were positive for the lt gene, 51.51% for the st gene and 6.06% for both genes. These findings highlight the widespread presence of ETEC in fresh produce sold in Mexico City, posing a significant public health risk, particularly given the increasing consumption of raw vegetables. The study provides the first reported data on ETEC contamination ratios in Mexico City, emphasizing the urgent need for improved food safety measures, including better hygiene practices during production, handling and preparation of fresh produce. This research underscores the importance of ongoing surveillance and preventive strategies to mitigate the risk of foodborne diarrhoeal diseases in urban populations.