The global health community is concerned about the rise and spread of antibiotic resistance and evolution of new strains of disease-causing agents. As a result of restricted access to proper medicine, in many developing countries, people are still using plants to treat the most prevalent infections. In this study, antimicrobial activities of methanol (75%), ethanol (95%) and aqueous extracts from leaves, raw fruit as well as ripe fruit of Psidium guajava extracts were investigated against Escherichia coli MTCC45, Klebsiella pneumoniae MTCC9544 and Bacillus subtilis MTCC121. The antimicrobial activities of the extracts against bacteria were tested by using agar well diffusion and agar disc diffusion method. The ethanolic and methanolic extract of P. guajava leaves shows activity against K. pneumonia (MIC= 25 mg/ml and 75 mg/ml respectively). The methanolic and ethanolic extract of raw fruit shows activity against K. pneumonia and E. coli (MIC= 50 mg/ml and 75 mg/ml respectively). The aqueous, methanolic and ethanolic extract of ripe fruit shows a significant MIC value of 50 mg/ml, 25 mg/ml and 25 mg/ml respectively against E. coli. The ethanolic extract of leaves and aqueous extract of ripe fruit shows activity against B. subtilis (MIC= 50 mg/ml and 75 mg/ml respectively). The ethanolic and methanolic extracts showed higher antimicrobial activity as compared to aqueous extracts. The phytochemical analysis shows that various extracts from leaves, raw fruits and ripe fruits of P. guajava contains tannin, phlobatannins, saponins, terpenoids , flavonoids, polyphenols, reducing sugar and alkaloid. Results from the present study showed that P. guajava extracts possess potent antibacterial activity against pathogenic microbes such as B. subtilis, K. pneumonia and E. coli. These extracts can become good sources for isolation and purification of natural antibiotic compounds and hence may yield natural alternative therapeutics.

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