Resumo

Staphylococcus aureus has been considered the most important human pathogen in the twenty-first century, due to its exceptional capacity to acquire resistance to antibiotics. This bacterium usually causes superficial skin infections and, occasionally, deep-seated infections that can spread through the blood stream and ultimately lead to sepsis. S. aureus infections are also associated with intravascular devices and foreign bodies. Taken together, these factors point to the urgent need of new antimicrobial agents against S. aureus. In this work we presented the inhibitory activity of Anadenanthera colubrina (ACHE), Libidibia ferrea (LFHE) and Pityrocarpa moniliformis (PMHE) fruit extracts against different clinical strains of S. aureus, the effects of extracts on cell constituents, the ultra-structural alterations involved and the combined action of erythromycin with extracts. The antimicrobial activity was evaluated by broth microdilution method. The bacteria were growth in the presence of extracts and morphological alterations were studied by Electron microscopy. The combinatory effects were determined by checkerboard method. The effects on bacterial DNA, the release of intracellular material (as indicative of membrane damage) and protein were detected. The samples were active of all S. aureus strains (MIC: 0.38 to 3.13 mg/mL) including the multiresistant strain. The morphological changes suggested the cell wall as the main action target. The treated-cells also lose their ability to form aggregates. The analysis suggests cell wall impairment which causes loss of viability and death. PMHE demonstrated synergistic effects in six ratios tested, while ACHE and LFHE had five and four proportions, respectively. The antagonistic effect was not found. The greatest synergistic potential of PMHE is related to its capability to cause damage in bacterial membrane. The protein release model changed along with all treatments, suggesting loss of cell viability and disturbs on metabolic pathways. This study showed at the first time the morphologic alterations involved in the anti-S. aureus action of fruits of A. colubrina and L. ferrea, P. moniliformis. These findings indicated that these fruit extracts are sources of bioactive compounds which can be used as antibacterial agents.