Antimicrobial resistance is a growing concern for both human and animal health, as well as the environment. Several countries established surveillance programs for antimicrobial use in animals and in Portugal we also have the PANRUAA, since 2014, that encourages antimicrobial use reduction in animals. As swine production is one of the food industries where the antimicrobial use deserves attention, we collected laboratory data from pig samples to obtain information on antimicrobial resistance in Portuguese swine production. Escherichia coli is an indicator bacteria of normal intestinal flora of swine and in this study, we used Escherichia coli isolates to analyze antimicrobial resistance. Our aim was to contribute to the knowledge of antimicrobial resistance frequencies in Portuguese swine farms.

Seventy seven strains of E. coli were isolated from intestinal swabs or stools of swine with symptoms of enteric pathology. Those samples came from 26 different farms and antimicrobial resistance was evaluated according to CLSI guidelines, by diffusion disc method.

All Escherichia coli strains were resistant to more than one antimicrobial. Lincomycin, Doxycycline, Amoxycillin, Ampicillin and Oxytetracycline were the antimicrobials with the highest frequency of resistant strains. The lowest frequencies of antimicrobials resitant strains were found for Neomycin, Gentamicin, Ceftiofur and Marbofloxacin. Comparing antimicrobials resistance frequencies from both years, we found a significant increase for Amoxycillin, Apramycin, Colistin, Oxytetracycline and Lincomycin - Spectinomycin. Our data supports other findings of high antimicrobial resistance for Tetracyclines and Penicillins in samples from Portuguese slaughters. The antibioresistance for these antimicrobials groups has also been reported in swine samples in other European countries. This study provides information that together with data from other Portuguese studies, potentiate the knowledge of the real state of antimicrobials resistance in swine production and the adjustment of the antimicrobials administration.