Antibacterial Activity of Guyabano, Ulasimang Bato, Sambong, and Tsaang Gubat Leaf Extracts against Common Drug-resistant Bacteria Cecilia C. Maramba-Lazarte, 1,2 Lolita L. Cavinta 2 and Ma. Carmelita L. Sara 1 1 Department of Pharmacology and Toxicology, College of Medicine, University of the Philippines Manila 2 Institute of Herbal Medicine, National Institutes of Health, University of the Philippines Manila ABSTRACT Background. Using plants as antmicrobials has long been a practce of traditonal healers and validatng these customs may lead to the discovery and development of useful herbal medicines. Objectve. This study aimed to determine the antbacterial actvity of guyabano, tsaang gubat, sambong, and ulasimang bato against common pathogens. Methods. Aqueous or alcoholic leaf extracts of the diferent medicinal plants were prepared. The solid agar diluton method was used to determine the MIC of guyabano, tsaang gubat, sambong, and ulasimang bato against common pathogens including Staphylococcus aureus, Echerichia coli, Streptococcus pneumoniae, Hemophilus infuenzae, Pseudomonas aeruginosa, Salmonella typhi, and Shigella fexneri. Results. The alcoholic leaf extract of guyabano showed moderate actvity against oxacillin-sensitve S. aureus with an MIC of 5-6.3 mg/mL. However, tsaang gubat did not exhibit any antbacterial actvity for drug-resistant enteric organisms (S. typhi, S. fexneri, and E. coli) and S. aureus at a concentraton of 25 mg/mL. Even at a concentraton of 100mg/mL, ulasimang bato failed to show any antbacterial actvity against drug-resistant S. aureus, S. pneumonia, H. infuenzae, E. coli, and P. aeruginosa. Sambong alcoholic extract had some antbacterial actvity against penicillin-resistant S. pneumoniae with an MIC of 12.5 mg/mL. Conclusions. Guyabano alcoholic leaf extract showed moderate antbacterial actvity against oxacillin-sensitve S. aureus. Sambong alcoholic extract likewise exhibited inhibitory actvity against S. pneumoniae. However, tsaang gubat and ulasimang bato aqueous extracts failed to show signifcant antbacterial actvity for the pathogens tested. Key Words: antbacterial actvity, guyabano, Anona muricata, tsaang gubat, Ehreta microphylla, Carmona retusa, sambong, Blumea balsamifera, ulasimang bato, pansit-pansitan, Peperomia pellucida InTRoDUCTIon Bacterial infections remain to be an important cause of morbidity in the Philippines with respiratory, gastrointestinal and urinary tract infections still being very prevalent. 1 Antibiotics have been used to treat bacterial infections and are considered one of the most important discoveries of the modern era. Unfortunately, because of extensive abuse and misuse of antibiotics both in humans and animals, rates of antimicrobial resistance have been increasing. According to a WHO Report in 2014, the top 7 common bacteria that cause serious diseases with widespread resistance include E.coli, S. aureus, H. infuenzae, Shigella, P. aeruginosa, non- typhoidal Salmonella, Klebsiella, and N. gonorrhea. 2 In the Philippines, Staphylococcus aureus, Pseudomonas aeruginosa, Corresponding author: Cecilia C. Maramba-Lazarte, MD, MScID, MScCT Insttute of Herbal Medicine Natonal Insttutes of Health University of the Philippines Manila 623 Pedro Gil St., Ermita, Manila 1000, Philippines Email: ccmaramba@up.edu.ph VOL. 54 NO. 1 2020 ACTA MEDICA PHILIPPInA 17 oRIGInAL ARTICLE