Int. j. food microbiol. Int. j. food microbiol. Resistance to colistin and production of extended-spectrum ß-lactamases and/or AmpC enzymes in Salmonella isolates collected from healthy pigs in Northwest Spain in two periods: 2008-2009 and 2018 Sevilla E. Vico J.P. Delgado-Blas J.F. González-Zorn B. Marín C.M. Uruén C. Martín-Burriel I. Universidad de Zaragoza Bolea R. Universidad de Zaragoza Mainar-Jaime R.C. Universidad de Zaragoza 2021 research-article