Iconic autochthonous breeds of cattle in Northern Portugal are reservoirs of multidrug-resistant ESBL-carrying Escherichia coli

Antimicrobial resistance (AMR) is a public health concern involving food-producing animals. Animals act as reservoir/source of antibiotic-resistant Escherichia coli that can spread to humans through the food chain or the environment.

This study aimed to characterize the AMR profiles of E. coli from fecal samples of three native Portuguese breeds (Barrosã, Cachena, and Minhota) since this information is non-existent.

From thirty extensive producing farms (10 per breed) in Northern Portugal, 480 collected samples (May-June 2023) were pooled, based on age group (8 calves and 8 cows per farm) and isolated on MacConkey Agar supplemented with or without antibiotics (4 µg/ml cefotaxime; 3 µg/ml colistin). A total of 102 characteristic E. coli colonies representing the 3 different breeds were selected for confirmation by MALDI-TOF MS, antimicrobial susceptibility testing (AST) for 10 antibiotics (EUCAST/CLSI guidelines), ESBL phenotype (DDST) screening and detection of blaTEM, blaSHV, and blaCTX-M genes by PCR.

From both calves and cows, 77% and 20% of the E. coli exhibited resistance to ≥1 antibiotic and multidrug resistance (MDR, resistance to ≥3 antimicrobial classes), respectively, from all breeds. Isolates were mostly resistant to gentamycin (72%), tetracycline (27%), and ampicillin (21%). ESBL activity was observed in 10% of E. coli isolates (from Cachena and Minhota breeds). Ongoing assays have already shown the presence of bla_TEM and bla_CTX-M genes for one isolate. This pioneering study revealed the concerning presence of MDR E. coli in iconic native Portuguese cattle breeds raised in production regimes where antibiotic use is theoretically low.