Evaluation of Psidium Guajava (Guava) Leaf Extract Against Gram-Negative Bacteria in Planktonic and Biofilm Lifestyles

Aims: To test and compare relative efficiencies of Guava Leaf Ethanolic Extract (GLEEx) and antibiotic standards against two pathogenic gram-negative bacteria in planktonic and biofilm lifestyles. Study Design: In vitro antibacterial study. Place and Duration of Study: Department of Biochemistry & Molecular Biology in the University of the Philippines Manila, between January 2014 and April 2014. Methodology: The susceptibility of planktonic and biofilm forms of Escherichia coli and Original Research Article Annual Research & Review in Biology, 4(24): 4370-4380, 2014 4371 Pseudomonas aeruginosa to GLEEx and to appropriate antibiotic standards were evaluated using the Kirby-Bauer disc diffusion assay (KB) and the Bio Timer Assay (BTA), respectively. Results: In KB, GLEEx exhibited comparable antibacterial strengths against both bacteria (P > .05), but was significantly less than the antibiotic standards (P .05). Conclusion: The relative antibacterial potencies of GLEEx and standard antibiotics vary depending on bacterial lifestyle, thus suggesting the need to use BTA alongside KB when assessing the antibacterial properties of natural products.