Abstract
The spread of antibiotic resistant bacteria throughout the food chain constitutes a public health concern. To understand the contribution of fresh produce in shaping antibiotic resistance bacteria and integron prevalence in the food chain, 333 antibiotic resistance Gram negative isolates were collected from organic and conventionally produced fruits (pears, apples, and strawberries) and vegetables (lettuces, tomatoes, and carrots). Although low levels of resistance have been detected, the bacterial genera identified in the assessed fresh produce are often described not only as environmental, but mostly as commensals and opportunistic pathogens. The genomic characterization of integron-harboring isolates revealed a high number of mobile genetic elements and clinically relevant antibiotic resistance genes, of which we highlight the presence of as mcr-1, qnrA1, blaGES−11, mphA, and oqxAB. The study of class 1 (n = 8), class 2 (n = 3) and class 3 (n = 1) integrons, harbored by species such as Morganella morganii, Escherichia coli, Klebsiella pneumoniae, led to the identification of different integron promoters (PcW, PcH1, PcS, and PcWTNG−10) and cassette arrays (containing drfA, aadA, cmlA, estX, sat, and blaGES). In fact, the diverse integron backbones were associated with transposable elements (e.g., Tn402, Tn7, ISCR1, Tn2*, IS26, IS1326, and IS3) that conferred greater mobility. This is also the first appearance of In1258, In1259, and In3-13, which should be monitored to prevent their establishment as successfully dispersed mobile resistance integrons. These results underscore the growing concern about the dissemination of acquired resistance genes by mobile elements in the food chain.
Highlights
The spread of antimicrobial resistance has made bacterial infections gradually more difficult to treat (Blair et al, 2015; Hawkey, 2015)
195 and 138 bacterial isolates were recovered from fruits and vegetables conventionally and organically produced, respectively
16S rDNA profiling revealed that the isolates were represented by 20 bacterial genera distributed among six main families of Gram negative bacteria, among which the predominant was Enterobacteriaceae (55.3%; Figure 1)
Summary
The spread of antimicrobial resistance has made bacterial infections gradually more difficult to treat (Blair et al, 2015; Hawkey, 2015). Increasing evidence suggests that intestinal microbiota of humans and animals constitutes a reservoir for antibiotic resistant bacteria and resistance genes (Hu et al, 2014). A better understanding on how antibiotic resistant bacteria break into the human microbiota is essential to prevent multidrug resistant infections. Vegetables and fruits can become contaminated with pathogenic and commensal bacteria from animals and humans. This contamination can occur in the field through direct contact with soil, and through the application of manure and wastewater as biofertilizers (Ben Said et al, 2015; Berendonk et al, 2015; van Hoek et al, 2015). It should be noted that fresh produce might become contaminated in stores, after distribution, through incorrect human manipulation (van Hoek et al, 2015)
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