Polymyxin-Resistant Escherichia coli Found in Vegetables from Brazil: An Emerging Public Health Concern

TL;DR

Polymyxin-resistant E. coli was found in vegetables in Brazil, raising concerns about the spread of antibiotic resistance through food.

Contribution

This study reports the first detection of polymyxin-resistant E. coli in vegetables in Brazil and identifies plasmid-mediated resistance.

Findings

Ten polymyxin-resistant E. coli strains were isolated from various vegetables in Brazil.

Four isolates transferred resistance via conjugation, indicating plasmid-mediated gene transfer.

Genome sequencing revealed multiple sequence types and the presence of mcr-1 gene-carrying plasmids.

Abstract

Vegetables are essential components of a healthy diet and are frequently consumed raw, which can facilitate the transmission of pathogens such as Escherichia coli. In addition to causing infections, E. coli can transfer resistance genes, such as mcr-1 (mobilized colistin resistance), to other microorganisms, conferring resistance to polymyxins. This study aimed to phenotypically and genotypically characterize polymyxin-resistant E. coli strains isolated from vegetables sold in Brazil. Among 514 samples analyzed, 10 E. coli strains exhibited polymyxin resistance: 5 from lettuce, 2 from chicory, and 3 from watercress, cabbage, and arugula. Broth microdilution revealed minimum inhibitory concentrations (MICs) of 4 µg/mL for eight isolates and 8–16 µg/mL for the remaining two. Antimicrobial susceptibility testing indicated a phenotype consistent with AmpC β-lactamase production, as seven isolates were resistant to cefoxitin, and whole-genome sequencing confirmed the presence of blaAmpC genes. Several isolates also showed resistance to other β-lactams, fosfomycin, and trimethoprim-sulfamethoxazole. Four strains successfully transferred polymyxin resistance via conjugation, suggesting plasmid-mediated gene transfer. Genome sequencing identified multiple sequence types (STs), with ST48 being the most prevalent, and detected two plasmids carrying the mcr-1 gene. Phylogenetic analysis revealed that these strains were related to diverse sources, including environmental and animal reservoirs. This study reports the presence of polymyxin-resistant E. coli in vegetables in Brazil, highlighting the zoonotic risk and the potential spread of resistance genes through mobile plasmids. These findings emphasize the need for continued surveillance of fresh produce to limit the dissemination of antimicrobial resistance and protect public health.

Figures