POPTENTIATION OF ANTIBIOTIC-ACTIVITY BY EDTA-TROMETHAMINE AGAINST 3 CLINICALLY ISOLATED GRAM-POSITIVE RESISTANT-BACTERIA - AN IN-VITRO INVESTIGATION

The in vitro synergistic effects of combinations of EDTA-tromethamine and five antimicrobial agents (ampicillin, cephalexin, oxytetracycline , streptomycin and sulphadimethoxine) on three clinically isolated Gra m-positive bacteria (Staphylococcus aureus, Staphylococcus hominis and Streptococcus faecium) were investigated. The bacteria had been isola ted from three cases of canine otitis resistant to beta-lactam antibio tic therapy. The antimicrobial activity was evaluated by measuring the minimal inhibitory concentration for the antibiotics alone or in comb ination with EDTA-tromethamine. EDTA-tromethamine potentiated the acti vity of cefalexin against S. aureus and S. hominis, of oxytetracycline against S. aureus and S. faecium and of streptomycin against S. faeci um. No significant effects were noted on the activity of oxytetracycli ne against S. hominis. The remaining combinations gave a slight synerg istic effect. As previously shown for Gram-negative resistant bacteria , these data suggest that the association of EDTA-tromethamine and app ropriate antibiotic therapy may be useful to overcome persistent infec tions of soft tissues in domestic animals.