Resumo

Bacterial infection causes high rate of mortality in human population. The use of antibiotics increased significantly due to heavy infections and the pathogenic bacteria becoming resistant to drugs is common due to indiscriminate use of antibiotics. There are reports of macroalgae derived compounds that have a broad range of biological activities. In this study, antibacterial efficacy of organic solvent extracts of the seaweeds Caulerpa racemosa, Jania adhaerens, Padina gymnospora, Sargassum polyceratium and Ulva lactuca against gram-positive and gram-negative human pathogenic bacteria species is reported. Crude extracts were prepared using different solvents namely, hexane, chloroform, ethyl acetate and methanol and were tested using disc diffusion method and minimum inhibitory concentration (MIC). A suitable positive control was also maintained. The seaweeds were collected by hand picking from the submerged marine rocks at Paiva Beach and Pedra do Xareu Beach, Cabo de Santo Agostinho municipality, Pernambuco State, Brazil. Voucher specimens of each species have been deposited at Instituto Agronômico de Pernambuco Herbarium (IPA). Maximum activities were recorded in the green marine algae U. lactuca ethyl acetate (23±0.00 mm) and methanol (20±0.00 mm) extracts and C. racemosa ethyl acetate (19±0.00 mm) and methanol (18±0.00 mm) extracts when compared to other solvent extracts as well as various solvent extracts of the marine algae J. adhaerens, P. gymnospora and S. polyceratium. Less inhibitory effects for all the test organisms were recorded in the J. adhaerens and P. gymnospora. Among the five marine algae tested, maximum activities were recorded in green marine algae U. lactuca and minimum activity was recorded in red marine algae. All the four solvent extracts of the marine algae, J. adhaerens and P. gymnospora were not revealed any activity against one gram-positive bacterial strains K. pneumoniae. A minimum value of MIC as 0.78 mg/mL was observed for S. aureus to the crude ethyl acetate extracts of U. lactuca and C. racemosa. It was observed that the ethyl acetate extracts of all the five marine algae showed higher inhibitory activity for the selected bacterial species than other solvent extracts. The results revealed that the crude ethyl acetate extracts seem to be a good source material in identifying the effective pure antibacterial compound(s) in all the five marine algae and particularly, C. racemosa and U. lactuca.