Bacterial resistance to antimicrobials has a significant influence on human and animal disease and health. It is a growing threat as more harmful bacteria become resistant to therapeutics. Bacteria producing Extended Spectrum Beta-Lactamases (ESBL) isolated from the intestines can be resistant to beta-lactam antibiotics (e.g. penicillin). Our aim is to isolate ESBL bacteria in mink, otters, and sea lions in two rivers in southern Chile and to determine their origin (e.g. pets).