# High Prevalence of Multidrug-Resistant Haemolytic Escherichia coli in Colombian Pig Farms

## TL;DR

Multidrug-resistant haemolytic E. coli is common in Colombian pig farms, with high resistance to multiple antibiotics and limited link to ETEC.

## Contribution

The study reveals high prevalence of MDR haemolytic E. coli in Colombian pig farms and challenges its use as an ETEC marker.

## Key findings

- 40.3% of samples contained haemolytic E. coli, highest in growing piglets.
- All isolates were multidrug-resistant, with over 90% resistance to tetracycline, neomycin, and chloramphenicol.
- Colistin resistance was found in 5.4% of isolates, mediated by mcr1 or mcr3.

## Abstract

Introduction: Haemolytic Escherichia coli (E. coli) is commonly associated with enteric disease in pigs and is frequently used as a phenotypic marker for enterotoxigenic E. coli (ETEC). This study aimed to characterise the resistance and virulence profiles of haemolytic E. coli isolated from Colombian pig farms. Methods: A total of 367 faecal samples from sows and pigs across all production stages were collected and analysed for the presence of haemolytic E. coli. Resistance and virulence genes associated with ETEC was detected by multiplex PCR, and antimicrobial susceptibility profiles were determined using broth microdilution and disc diffusion. Results: Haemolytic E. coli were identified in 40.3% of samples (n = 148 non-duplicate isolates), with the highest prevalence observed in growing piglets (47.1%). ETEC occurred in 5.4% of isolates. All isolates exhibited resistance to at least three antimicrobial classes (MDR), with high levels of resistance to tetracycline (98.0%), neomycin (97.3%), chloramphenicol (95.9%), sulfamethoxazole (93.9%), trimethoprim (91.9%), ampicillin (91.9%), nalidixic acid (82.4%), and ciprofloxacin (79.7%). Colistin resistance was observed in 5.4% of isolates, mediated by mcr1 or mcr3, while cefotaxime resistance (8.8%) was extensively associated with blaCTX-M. Conclusions: These findings reveal a concerning burden of MDR E. coli in Colombia’s pig-producing regions and indicate that haemolysis alone is a poor indicator of ETEC. Integrating farm-level antimicrobial use data with genomic analyses will be essential to identify drivers of AMR and guide effective stewardship in the Colombian pig industry.