Bioassay-Guided Discovery of Antibacterial Agents: In vitro Susceptibility of Multi-drug Resistant Staphylococcus aureus to Psidium guajava Linn Extracts

Aims: Development of multi-drug resistance to antibiotics is a major health concern worldwide. This study assessed the antibacterial activities of leaves extracts from Psidium guajava against multi-drug resistant Staphyllococcus aureus strains.

Study Design: Three (3) different extracts were prepared from the dried leaves of P. guajava and tested against the multi-drug resistant strains isolated from clinical samples.

Place and Duration of Study: Microbiology department, Centre for Plant Medicine Research. From October 2014 to March 2015.

Methodology: Absolute ethanol, 70% ethanol and aqueous extracts were prepared using maceration and concentrated by rotary evaporation techniques. The lyophilized materials were reconstituted in serial concentrations for antimicrobial assessments using the agar well diffusion method. The minimum inhibition concentration was determined by broth microdilutions method.

Results: Although, all the 14 strains exhibited various antibiotypes to 10 different commonly used antibiotics; none of them was resistant to the 3 extracts. There was 1/14 (KTHMDR-5) strain being highly susceptible to aqueous extract. In addition, the absolute ethanol extract was effective against 8/14 strains at 25 mg/ml and 4/14 strains at 12.5 mg/ml, whiles the aqueous extract was effective against 13/14 strains and 11/14 strains at 25 and 12.5 mg/ml respectively. The 70% ethanol extract showed much stronger activity against all the 14 strains than the aqueous and absolute ethanol extracts from 200 to 25 mg/ml with only 1/14 strain (KTHMDR-2) not being sensitive at a concentration of 12.5 mg/ml. The MIC values for all the strains were considerably low ranging from 0.78 to 6.25 mg/ml. There was a very strong significance difference (P < 0.0001) between the antimicrobial activities of 70% ethanol extract and the absolute ethanol.

Conclusion: The 14 multi-drug resistant S. aureus strains were susceptible to the 3 extracts with 70% ethanol extract exhibiting the most significant antimicrobial activity. Therefore, it is important to utilize this extract in drug formulations.