Antibiotic resistance in enterotoxigenic and enteroaggregative E. coli causing traveler’s diarrhoea: a genotypic and phenotypic correlation study

Traveler’s diarrhea (TD) remains one of the most prevalent health concerns affecting individuals visiting low- and middle-income countries. TD is mainly caused by infectious agents, particularly enteroaggregative E. coli (EAEC) and enterotoxigenic E. coli (ETEC). The aim of this study is to characterize antibiotic resistance patterns and underlying resistance mechanisms in EAEC and ETEC isolates causing TD (2018-2023).

A total of 46 ETEC and 44 EAEC strains isolated from TD patients attending Hospital Clínic (Barcelona) were analyzed. Antibiotic resistance profiles were determined using phenotypic methods based on minimum inhibitory concentration (MIC) and genotypic analysis by whole-genome sequencing using Illumina technology.

Phenotypic resistance patterns were similar between pathotypes, except for levofloxacin (LEV), ciprofloxacin (CIP) and ceftriaxone (CRO), for which ETEC showed higher resistance rates. Among EAEC isolates, resistance rates were: cefepime (FEP) 9.1%, cefazolin (FAZ) 50%, ceftazidime (TAZ) 13.6%, CRO 11.4%, ampicillin (AMP) 52.3%, aztreonam (AZT) 18.2%, LEV 2.3%, CIP 2.3%, and trimethoprim/sulfamethoxazole (SXT) 61.4%. In ETEC isolates, resistance rates were: FEP 17.4%, FAZ 65.2%, TAZ 17.4%, CRO 21.7%, AMP 52.2%, AZT 19.6%, LEV 13.3%, CIP 13%, and SXT 43.5%. All phenotypically resistant isolates showed corresponding genotypic resistance mechanisms. For β-lactams, the most frequent mechanisms were TEM-1 (n=32) and CTX-M-15 (n=13). The dfrA gene was identified in SXT-resistant isolates, while mutations in gyrA and parC were responsible for LEV and CIP resistance. Isolates acquired in Asia showed the highest overall resistance rates, whereas SXT resistance was more frequent in isolates from Africa.

The dissemination of multidrug-resistant EAEC and ETEC through international travel represents a significant risk for the spread of antimicrobial resistance, both through the introduction of multidrug-resistant strains and via the dissemination of resistance genes carried on mobile genetic elements. This risk appears to be elevated in Asia and Africa, highlighting the need for continuous surveillance and antimicrobial stewardship in TD management.