Antimicrobial Resistance of Escherichia coli Isolates in Romaine Lettuce from Vegetable Markets in Marilog District, Davao City, Philippines

Abstract

The consumption of lettuce (Lactuca sativa L.) has become a trend due to its health benefits. However, lettuce, in general, has been described as a reservoir of pathogenic microbes such as antimicrobial-resistant (AMR) E. coli, posing a health risk to consumers that may lead to an outbreak of foodborne pathogens. The MPN test was used for coliform enumeration. E. coli isolation used membrane filtration techniques and subculture techniques, confirmed by gram staining. The antimicrobial susceptibility profiles of the E. coli isolates were determined using the Kirby-Bauer disk diffusion assay. A Chi-square test of independence correlated coliform contamination and AMR. The study found that among the 50 Romaine lettuce samples, the average level of coliform contamination was 693.52 MPN/g, a value above the acceptable limit in vegetables. Among the E. coli isolates, 60% were susceptible to amikacin (30 µg), and 90% were susceptible to nalidixic acid (30 µg). AMR E. coli isolates were found, with 85% resistant to ampicillin (10 µg), 40% resistant to ticarcillin (75 µg), 15% resistant to cefazolin (30 µg), and 45% expressing multidrug resistance. The Chi-square test of independence showed that coliform contamination and AMR had a significant relationship, with AMR found more frequently in samples with low MPN/g. This study emphasizes the need for surveillance of AMR bacterial strains in fresh produce and the implementation of better sanitary practices in the post-harvest handling of lettuce.