Antimicrobial resistance in Portuguese broiler-breeder flocks between 2009 and 2018

In poultry, colibacillosis is one of the most economically impactful diseases and it is caused by avian pathogenic E. coli (APEC) strains. In this study, we evaluate APEC antimicrobial resistance and its evolution over a period of ten years with the collection of 264 positive samples. All the samples were collected from broilerbreeder flocks that exhibited signs of disease. We found a very high resistance prevalence for amoxicillin and ampicillin, both above 70% which was not to be expected. Tetracycline also had a high resistance value of 63.3%. Multidrug-resistance (MDR) was present in 84% of tested strains. Despite these values, the general trend of all tested antimicrobials indicates that resistance levels have been decreasing, or at least, being stable over these ten years.