Title : Vegetable-associated Escherichia coli ST446 carrying blaCTX-M-1 and mcr-1 raises concerns regarding difficult-to-treat foodborne infections
Abstract:
Antimicrobial resistance is a pressing global issue with significant implications for human health. The presence of human bacterial pathogens resistant to last-line treatments in ready-to-eat vegetables is particularly concerning, as it compromises food safety and poses a serious threat to public health. In this study, an Escherichia coli strain (P13) isolated from a cabbage leaf obtained from a cultivation area in Serrana, São Paulo, Brazil, was characterized phenotypically, molecularly, and genomically. Cabbage leaves were processed in saline solutions by shaking to obtain epiphytic bacteria. Selective isolation was performed on MacConkey agar plates supplemented with 4 mg/L of ceftriaxone, and genomic DNA was extracted using a silica column-based purification procedure. Molecular identification was performed by 16S rRNA sequencing. Antimicrobial susceptibility was determined using disk diffusion and broth microdilution methods following the Brazilian Committee on Antimicrobial Susceptibility Testing/European Committee on Antimicrobial Susceptibility Testing (BrCAST-EUCAST, v.10.0, 2024) guidelines. Whole-genome sequencing was performed using Oxford Nanopore Technologies, and de novo genome assembly was conducted using Flye v.2.9.1. Genomic characterization, including antimicrobial resistance genes (ARGs), virulence determinants, multilocus sequence typing, serotyping, phylogroup, and plasmid detection, was performed using tools available from the Center for Genomic Epidemiology. The P13 strain exhibited resistance to ampicillin, amoxicillin-clavulanic acid, ampicillin-sulbactam, cefazolin, ceftriaxone, cefotaxime, ceftazidime, cefepime, aztreonam, nalidixic acid, norfloxacin, streptomycin, tetracycline, doxycycline, minocycline, trimethoprim-sulfamethoxazole, and fosfomycin. Notably, this strain showed a minimum inhibitory concentration of 4 mg/L for colistin, demonstrating resistance to this antimicrobial. Accordingly, the P13 strain harbored the following ARGs: blaCTX-M-1 (β-lactam resistance, including third-generation cephalosporins), mcr-1 (polymyxin resistance), aadA (aminoglycoside resistance), sul2 (sulfonamide resistance), and tetA and tetB (tetracycline resistance). Additionally, this strain presented a mutation in GyrA (S83L) related to fluoroquinolone resistance. Strain P13 belonged to the sequence type (ST) 446, serotype O54:H32, phylogroup A, and harbored two plasmid replicons, IncI1 and IncX4. Moreover, this strain carried several virulence determinants, highlighting those related to adhesion and biofilm formation (fimH, csgA), bacteriocin production (cea, cib), cytotoxicity (hlyE), immune evasion (ompT), and stress tolerance (gad, terC). These results highlight the presence of a potentially virulent E. coli ST446, a One Health clone linked to human infections, harboring ARGs associated with resistance to last-line antimicrobials at the food-health interface. Therefore, these findings underscore the importance of surveillance and control measures along the vegetable production chain to ensure food safety and protect human health.
