Antimicrobial activity of dimeric acylphloroglucinols isolated from southern Brazilian Hypericum species against to resistant bacterial.

The hexanic extracts of Hypericum austrobrasiliense, H. caprifoliatum , H. denudatum , H. pedersenii and H. polyanthemum , and three isolated dimeric acylphloroglucinols (uliginosin B, japonicine A and hyperbrasilol B) were assayed for their antimicrobial activity against some Gram-positive and Gram-negative bacteria (including resistant strains). These extracts were assayed using the disc diffusion test, and the results indicated that the tested species did non exhibit activity on the Gram-negative strains. Subsequently, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were measured using the broth dilution technique adopted to macrodillution. The most susceptible strains were the MRSA and the S. aureus MLSb. Regarding these pathogens, the better MIC values were obtained with the extracts from H. austrobrasiliense, H. caprifoliatum and H. pedersenii . The acylphloroglucinols uliginosin B and hyperbrasilol B presented the lowest MIC values against Enterococcus faecalis , Staphylococcus aureus , MRSA and S. aureus MLSb resistance.