objective. To identify Gram-negative bacteria with resistance to antibiotics isolated from infections associated to health care in a tertiary hospital in the city of Cali, which can be inferred to the predominant resistance mechanism. materials and method. Susceptibility data was obtained from 1,899 isolates of enteric Gram-negative bacteria of the Enterobacteriaceae family and non-fermenting lactose bacteria, during 2007-2008. results. The most frequent isolates were E. coli, K. pneumoniae and P. mirabilis with variable resistance to s-lactams except carbapenems. Ps. aeruginosa showed simultaneous resistance to s-lactams (including imipenem) and aminoglycosides, but susceptibility to quinolones and meropemen. Simultaneous resistance to cefoxitin, third generation cephalosporins, β-lactamase inhibitors and susceptibility to cefepime observed in isolates of P. mirabilis, E. aerogenes, C. freundii and K. pneumoniae is probably due to production of β-lactamase Amp C. Resistance to cephalosporins of third and fourth generation, aztreonam and β-lactamase inhibitors in isolates of E. coli, Ps. aeruginosa, E. cloacae, C. freundii, M. morganii and K. pneumaniae, suggests ESBL-mediated resistance. conclusions. The high resistance to aminoglycosides, inhibitors of DNA, and production of s-lactamases may be related to the indiscriminate use of these antibiotics in the hospital. The interpretation of susceptibility can be inferred to underlying resistance mechanisms, allowing not only to guide the antibiotic treatment, but helping predict which antibiotics could not be appropriate, taking into account the most likely underlying mechanism.