Detection of indicator and pathogenic bacteria in raw vegetables and fruits sold in fresh markets and supermarkets, Bangkok, Thailand

Abstract

This study aimed to compare the concentrations of fecal coliforms and Escherichia coli, and the contamination of Salmonella, Shigella, E. coli O157: H7 and Listeria monocytogenes in raw vegetables and fruits between fresh markets and supermarkets in Bangkok, Thailand. A total of 405 produce samples, consisting of sweet basil, spring onion, coriander, cabbage, lettuce, cucumber and tomato, were randomly collected from seven fresh markets (n=203) and 29 supermarkets (n=202) in seven districts of Bangkok between June 2018 and July 2019. T-test and one-way ANOVA were used to compare the concentrations of fecal coliforms and E. coli (log10MPN/g) between fresh markets and supermarkets, and among different types of samples. Chi-square test was used to compare the prevalence of pathogenic bacteria between fresh markets and supermarkets, and among different types of samples. Overall, the average concentrations (±S.D.) of fecal coliforms and E. coli were 2.97 (±2.03), and 2.49 (±1.98) log10MPN/g. The prevalence of Salmonella was 7.16%, while Shigella, E. coli O157: H7 and L. monocytogenes were not detected in the samples. The concentrations of fecal coliforms and E. coli were significantly higher in fresh markets (3.85 and 3.41 log10MPN/g) than in supermarkets (2.08 and 1.57 log10MPN/g) (P<0.001). The prevalence of Salmonella in fresh markets (9.36%) was higher than those in supermarkets (4.95%) (P=0.085). The average concentrations of fecal coliforms and E. coli of sweet basil, coriander, and lettuce were significantly higher than spring onion, cabbage, cucumber and tomato. This maybe because sweet basil, coriander, and lettuce are leafy vegetables normally grown and harvested in proximity with the ground, while cucumber and tomato are vining crops, which are harvested off the ground. Cabbage consists of thick and compact leaves which could prevent bacterial contamination. This result indicated that the produce collected from supermarkets had better sanitation and met microbiological standard than fresh markets. Therefore, effective control measures should be implemented to meet microbiological standards and secure the safety of raw produce consumption in Thailand.