Abstract

Enterobacteriaceae are the main etiological agents of environmental bovine mastitis and are often resistant to antimicrobials, especially β-lactam class due to the production of β-lactamases. These can be classified into several groups according to the molecular structure and substrate activity. The present study evaluated the profile of pheno-genotypic resistance to β-lactams, with emphasis on the functional detection of β-lactamases. The isolates were obtained from milk samples from farms located in the interior region of the state of Rio de Janeiro. 47.6% (20/42) of the bacterial isolates producing enzymes classified as Group 1 (AmpC type) were detected, and in disk approximation test, 30% were classified as the inducible type and 70% as not inducible. To the best of the authors’ knowledge, this is the first report on AmpC β-lactamase production in enterobacteria involved in mastitis etiology in Brazil.

Key words: Raw milk, environmental mastitis, dairy cattle, antimicrobial resistance.