ABSTRACT
BACKGROUND: Guava is a native plant in the Philippines and is available throughout the year. Several studies show that it exhibits anti-microbial activity on different bacteria. However, little is known on its anti-MRSA activity. The leaves of this plant if proven to have antibacterial properties against MRSA would be a very cost-effective drug against MRSA infected wounds.METHODS: This study determined the in vitro antimicrobial activity of a 50 percent solution of the lyophilized guava leaf crude aqueous extract on Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-sensitive Staphylococcus aureus (MSSA) in comparison with 30 mg vancomycin and 10 mg fusidic acid. The inhibitory effects of the three treatments were tested on two reference strains (MRSA ATCC 43300 and MSSA ATCC 25923), and four clinical MRSA isolates (1 MRSA from blood, and 3 MRSA from wound), using Disc Diffusion Assay. Microdilution Broth Assay was done to determine the Minimum Inhibitory Concentration (MIC) of guava extract and vancomycin.RESULTS: The highest inhibition was observed in fusidic acid (36 mm) followed by guava (21 mm) and then by vancomycin (18 mm). Vancomycin and guava have the same inhibitory effects against MSSA reference strain and MRSA wound 2 isolate. The effects of the three treatments on MRSA reference strain are comparable with all the clinical MRSA isolates. Guava is more effective to MRSA reference strain (24.6 mm) than MSSA reference strain (17.6 mm). However, vancomycin and fusidic acid have the same effects on both MRSA and MSSA reference strains. The effects of guava and fusidic acid on all clinical MRSA isolates (20.25 mm and 36.85 mm, respectively) are greater than their effects on MSSA ATCC 25923 (17.6 mm and 32.2 mm, respectively). Furthermore, Microdilution Broth Assay results showed that using 50 percent guava solution utilizing 1X10 exponent 8 CFU/ml, too many to count colonies were observed while there was inhibition of growth at 1X10 exponent 5 and 1X10 exponent 4 CFU/ml concentrations. Thus, it could then be probable that the MIC of lyophilized guava extract is 50 percent using bacterial concentrations ranging from 10 exponent 8 to 10 exponent 6 CFU/ml. However, colony formation was observed for 2 mg vancomycin utilizing 1X10 exponent 4 CFU/ml.CONCLUSION: Fifty percent (50 percent) solution of the lyophilized leaf crude aqueous extract inhibited the growth of methicillin-resistant Staphylococcus aureus and methicillin-susceptible Staphylococcus aureus. The efficacy of guava as an antimicrobial agent on both MRSA and MSSA strains is greater than vancomycin but lower than fusidic acid. Based on the in vitro results, guava can be considered as a good alternative medication for Staphylococcal infection especially with drug resistant Staphylococcus aureus strains. MIC of guava extract was confirmed to be 50 percent utilizing bacterial concentrations ranging from 1X10 exponent 8 and 1X10 exponent 6 CFU/ml. (Author)