Resumo

The multi-drug resistant (MDR) strains emergence is a phenomenon occurring worldwide, due to the selective pressure exerted by extensive use of antibiotics and that has hindered the bacterial infections treatment. Methicillin resistant S. aureus (MRSA) are MDR strains that cause potentially fatal systemic diseases and skin infections and they have been isolated with high frequency from hospital environment. Moreover, in recent years has increased the number of infections caused by community-acquired MRSA. This problem has moved the searches of new antibiotics or new compounds able of change the MDR phenotype. The specie Anadenanthera colubrina, var. cebil (Fabaceae) is a tree known locally as angico. It has been used in traditional medicine as remedy for gastrointestinal and respiratory disorders as well as for allergy treatment. The A. colubrina dichloromethane fraction (ACDCM) was tested for their antimicrobial activity alone or in combination with conventional antibiotics used in the treatment of infectious diseases caused by Staphylococcus aureus. The natural product didn’t show antimicrobial activity against multi-drug resistant strain at the clinically significant concentrations tested, once the minimal inhibitory concentration (MIC) was >1024 µg/mL. On the other hand, a synergistic effect was verified when ACDCM was used in association with Neomycin and Amikacin for MRSA. The MIC values for Neomycin and Amikacin alone were 1250.0 and 787.5 µg/mL, respectively. These were reduced to 496.1 and 98.4 µg/mL, respectively, when they were associated with the ACDCM against MRSA. A similar synergism was observed when the natural products were changed for chlorpromazine, a drug able to inhibit efflux pumps, suggesting the involvement of resistance mediated by efflux system. On the other hand the ACDCM showed an antagonistic synergistic effect when used in association with tetracycline. These results indicate that the hexane fraction of A. colubrina, var. cebil could become a promising natural product how a modifier agent of resistance to aminoglycosides.