Prevalence and Antimicrobial Characteristics of Escherichia coli in Selected Vegetables and Herbs in Bangkok, Thailand

Abstract

Raw vegetables and herbs are exposure sources of foodborne pathogens. This study examined the prevalence and antimicrobial resistance of Escherichia coli in five types of fresh vegetables and herbs: spearmint (Mentha spicata), leaf lettuce (Lactuca sativa var. crispa), coriander (Coriandrum sativum), Chinese cabbage (Brassica rapa subsp. pekinensis), and cucumber (Cucumis sativus). Produce samples (n = 300) were acquired from local open markets and supermarkets in Bangkok, Thailand. Each produce sample was preenriched in buffered peptone water and then enriched in E. coli broth. A loopful of the second enrichment was transferred onto selective media for subsequent confirmation and biochemical tests. The Kirby-Bauer disk diffusion test was employed to assess E. coli susceptibility to selected antibiotics (twelve antibiotics of seven classes). The latex agglutination test was performed to serotype the isolates for O157 and H7 antigens. A commercial test kit was used to determine the presence of Shiga toxin-producing E. coli (STEC). For all samples, the prevalence of E. coli was found to be 32.0% (96/300), whereby produce from supermarkets had a higher prevalence than those from local markets at 40.7% (61/150) and 23.3% (35/150), respectively. Among different types of produce, leaf lettuce had the highest E. coli prevalence at 36.7% (22/60), followed by cucumber and spearmint, coriander, and Chinese cabbage, at 35.0% (21/60), 35.0% (21/60), 35.0% (21/60), and 18.3% (11/60), respectively. Of the positive isolates, 27.1% (26/96) showed multidrug resistance. All isolates (100%) showed resistance to penicillin but varying resistant characteristics for tetracycline, ampicillin, and amoxicillin, with resistance rates of 31.3% (30/96), 31.3% (30/96), and 31.3% (30/96), respectively. Two of the 96 isolates (1.1%) were positive for the O157 antigen but negative for the H7 antigen. No STEC was observed. This study established baseline information regarding the prevalence of E. coli and its antimicrobial resistance profile in produce in Bangkok, Thailand.

Keywords: Bangkok; Escherichia coli; Herbs; Thailand; Vegetables.