Investigating Salmonella enterica, Escherichia coli, and Coliforms on Fresh Vegetables Sold in Informal Markets in Cambodia

Vegetables in Cambodia are commonly sold in informal markets lacking food safety standards and controls. Currently, data on microbial contamination of vegetables in Cambodian informal markets are limited. The purpose of this study was to investigate Salmonella enterica and indicator organisms (generic Escherichia coli and coliforms) on the surface of fresh vegetables sold in informal markets in Cambodia. A sample of loose-leaf lettuce, tomatoes, and cucumbers were collected from 104 vendors at four informal markets in Battambang and Siem Reap provinces during rainy and dry seasons. Detection methods for Salmonella enterica were adapted from the Food and Drug Administration's Bacteriological Analytical Manual (FDA BAM). Quantification of coliforms and generic E. coli populations was conducted by plating onto E. coli/Coliform count plates. Salmonella enterica was most prevalent on lettuce during the dry season (56.5%, 95% CI [41.0, 70.8]) compared to the rainy season (15.4 95% CI [7.5, 29.1]), whereas no significant seasonal differences were apparent for tomatoes and cucumbers. Regardless of season, levels of Salmonella enterica were highest on lettuce (5.7 log CFU/g, 95% CI [5.5, 5.9]), relative to cucumbers (4.2 log CFU/g, 95% CI [3.8, 4.6]) and tomatoes (4.3 log CFU/g, 95% CI [4.1, 4.6]). For generic E. coli, prevalence was higher during the rainy season (34.0%, 95% CI [25.4, 43.8]) as compared to the dry season (9.1%, 95% CI [4.9, 16.5]), with the highest prevalence estimated on lettuce. Similarly, the level of coliforms on lettuce and tomatoes was greater during the rainy season (6.3 and 5.3 log CFU/g, 95% CI [5.7, 6.8] and [4.7, 5.8], respectively), relative to the dry season (5.2 and 3.9 log CFU/g, 95% CI [4.7, 5.7] and [3.4, 4.4], respectively). In summary, these results indicate seasonal patterns for microbial prevalence in lettuce, and an overall high level of bacterial contamination on raw vegetables sold in Cambodian informal markets.