Abstract
The contamination of fresh produce with antibiotic-resistant bacteria is of particular concern as they are often eaten raw and can be a source for foodborne diseases. Tetracyclines have been largely used in humans, animals and plants which might have accelerated microbial resistance to them. Enterococci and Escherichia coli can be used as indicators to monitor contamination of the fresh produce with tetracycline-resistant bacteria. The investigation related to this issue is very scarce in Oman. This study aimed at identifying tetracycline-resistant enterococci and E. coli in fresh produce at the market place. Thirty-one enterococci and ten E. coli were isolated from local (Oman) and imported fruits and vegetables (N= 105). Using the standard Kirby-Bauer disc diffusion method, resistance to tetracycline was found in 6 (19 %) enterococci, isolated from cucumber, lettuce and radish, and 5 (50 %) E. coli, obtained from cabbage, lettuce and radish. Genetic analysis revealed the presence of tetracycline resistance genes, tet(A) and tet(K), in E. coli and tet(K), tet(L) and tet(M) in enterococci, including Enterococcus sulfureus, Enterococcus mundtii, Enterococcus casseli avus and Enterococcus faecalis. The integron integrase IntI 1 gene, which is known to facilitate the dissemination of antibiotic resistance genes among bacteria, was detected in 2 isolates of E. coli. These results demonstrated the capability of fresh produce to act as a potential source for disseminating tetracycline or possibly other antibiotic-resistant bacteria through the food chain. Thus, control strategies are needed to reduce exposure of the public to such microorganisms.
Highlights
Tetracyclines (TEs) are amongst the most important antibiotic groups used in medicine (Hernandez et al, 2003)
Twenty-nine percent of Enterococcus faecium isolated from fresh produce grown in the United States of America were found to be resistant to TE while all E. faecalis isolates were susceptible to TE (Johnston & Jaykus, 2004)
As the results of this study demonstrated the presence of different types of tet genes in enterococci and E. coli isolated from fresh produce at the market place, these bacteria may colonize the intestine and affect the tet resistance pool especially if the tet genes can persist in the gut for a long time (Forslund et al, 2013)
Summary
Tetracyclines (TEs) are amongst the most important antibiotic groups used in medicine (Hernandez et al, 2003) They exhibit a broad spectrum of activity against Gram-positive and Gram-negative bacteria, chlamydiae, rickettsiae, nematodes, mycoplasmas and protozoans. They inhibit protein synthesis in bacterial cells (Hernandez et al, 2003; Markley & Wencewicz, 2018) by preventing attachment of aminoacyl-tRNA to the acceptor (A) site of the ribosome. Horizontal gene transfer (HGT) among bacteria plays an important role in the dissemination of multidrug resistance, especially when antibiotic resistance genes (ARG) are located on mobile genetic elements such as plasmids and transposons. The aim of this study was to identify phenotypic and genotypic TE resistance in enterococci and E. coli that we previously isolated from different types of locally pro-
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