Composição química e atividade antibacteriana in vitro de extratos metanólicos obtidos de folhas e frutos de Rubus grandifolius Lowe

Abstract

Rubus grandifolius Lowe (Rosaceae Juss.) is a plant species found endemic and exclusively in the Madeira Archipelago, Portugal. Its fruits have great commercial value for the food industry, being used in the production of jellies, juices and liqueurs. Traditionally, the local population uses its leaves, flowers and fruits as an astringent for children and as a medicine to treat diabetes, depurative, diuretic, tonic and to relieve sore throats, being also used in the preparation of teas or alcoholic infusions. Based on the above, this study aimed to investigate the chemical composition and in vitro antibacterial activity of methanol extracts obtained from leaves and fruits of R. grandifolius. Leaves and fruits were extracted in methanol and methanol/water (80:20, v/v) acidified with 7% acetic acid, respectively. The chemical profiles of R. grandifolius leaf and fruit extracts were established by liquid chromatography coupled with mass spectrometry (HPLC-DAD-ESI/EMn ) and revealed the presence of several classes of phenolic compounds, including phenolic acids, tannins, flavonoids, organic acids, terpenoids and coumarins. As for the microbiological aspect, initially, twenty methanolic extracts obtained from different plant species from Madeira Island and Azores, Portugal, were screened for the in vitro antibacterial activity by determining the Minimal Inhibitory Concentration (MIC) and the Minimal Bactericidal Concentration (MBC) followed by the classification of the antibacterial effect as bactericidal or bacteriostatic. Staphylococcus aureus subsp. aureus [(ATCC 6538), (ATCC 25923) and (ATCC 29213)], Escherichia coli [(ATCC 10536) and (ATCC 25922)], Salmonella enterica subsp. enterica serovar Choleraesuis (ATCC 10708), Salmonella enterica subsp. enterica serovar Typhimurium (ATCC 13311) and Pseudomonas aeruginosa [(ATCC 9027) and (ATCC 27853)] were tested. Five most promising extracts were selected and subjected to further determination of MIC and MBC using human clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) 1485279, Salmonella spp. 1507708 resistant to levofloxacin, Escherichia coli 2856403 extended spectrum β-lactamase producer and resistant to ciprofloxacin and norfloxacin and Pseudomonas aeruginosa 2854386 resistant to cefoxitin, ceftriaxone and tigecycline. The R. grandifolius fruit extract was the most effective among all evaluated extracts, being active against all ATCC® strains tested, with a MIC value equal to 5000 µg/mL, except for S. aureus (ATCC 6538) (MIC = 2500 µg/mL), and bacteriostatic effect, with the exception of P. aeruginosa [(ATCC 9027) and (ATCC 27853)], where a bactericidal effect was observed. Regarding human clinical strains, the extract of R. grandifolius fruits was active against all strains tested, with MIC equal to 5000 µg/mL and bacteriostatic effect, with the exception of P. aeruginosa 2854386, which showed a bactericidal effect. The results obtained in the present study demonstrated that R. grandifolius, especially the extract obtained from its fruits, was able to inhibit the growth of ATCC® and human clinical strains of S. aureus, E. coli, Salmonella and P. aeruginosa, with a bactericidal effect on this last strain