Abstract

Since antimicrobials are used to fight infectious diseases, their proper use is a major world concern. The use of more than one medicine in the treatment of infectious disease is controversial hence the association therapy is used empirically to treat severe infections when one antimicrobial alone is not sufficient to account for all possible pathogens involved in the infection. The importance of understanding the mechanisms of gentamicin and ampicillin antibiotic action, as well as their interactions has important therapeutic implications. This research aimed to verify isolated and simultaneous antimicrobial action “in vitro” of gentamicin and ampicillin on strains of Enterococcus sp. in patients with Enterococcus sp.  Fifty strains of Enterococcus sp. were used to determine the minimum inhibitory concentrations (MIC) and minimum bactericidal concentration (MBC) of ampicillin and gentamicin, both isolated and associated, from which the fractional inhibition coefficient (FIC) was determined. A modified checkerboard method was also used for evaluating the association of the two antimicrobial agents. The results revealed that the antibiotics have a time- and dose-dependent response, and ampicillin has better results isolated than when in association. The results indicate a potential therapeutic failure in 32% of the associations in these agents. Thus, the most effective pharmaceutical care is facilitated by determining the antibiotics concentrations. Determining the MIC, MBC and FIC can be a powerful tool for guiding strategies to prevent bacterial resistance through the rational use of antibiotics, thereby averting and avoiding therapeutic failures.

Key words: Drug antagonism, drug synergism, Enterococcus sp., microbial sensitivity tests.