Phytochemical screenings, antibacterial and anti-biofilm activities of Garcinia cowa Roxb. leaves extracts and its synergistic effect with antibiotic

The rapidly growing antimicrobial resistance is a global problem. This made it necessary to search for new antimicrobial agents. In present study, agar well diffusion, broth microdilution and time-kill kinetic assays were used to determine the antimicrobial activities of the extracts against seven pathogens. The results showed that 75% acetonic and 95% ethanolic extracts of Garcinia cowa Roxb. leaves (GCL) showed the strongest broad-spectrum antibacterial effect towards both Gram-negative and Gram-positive bacteria with 9.67±0.57-22.83±0.45 mm of inhibition zones and MIC/MBC values ranging from 25-100 mg/mL. 95% ethanolic extract revealed the inhibiting and killing actions at rapid first 3 h of incubation, depending on concentration of extracts and had the best capacity to inhibit biofilm formation of all tested bacteria (gastrointestinal and urinary pathogens) with 73.43  0.20-90.14  0.10%. Pseudomonas aeruginosa ATCC 27853 displayed the highest sensitivity with all GCL extracts. Interestingly, 95% ethanolic extract and ampicillin combination showed a synergistic effect at FICI value of 0.0313-0.5 (1/16MIC×1/32MIC-1MIC×1/4MIC) against all microorganisms. The bioactive potency of constituents of the 95% ethanolic extract (saponins, tannins, flavonoids, steroids, terpenoids and alkaloids) play an important roles in the observed antibacterial, anti-biofilm and synergistic activities. The findings indicated that Garcinia cowa Roxb. leaves extracts had the strong broad-spectrum antibacterial, anti-biofilm and synergistic activities. Crude extracts possess time and concentration-dependent bactericidal actions. Thus, the present results that G. cowa Roxb. leaves extracts had potential as a natural alternative antimicrobials for fighting bacterial infections.