Research Article Synergistic Interaction of Methanol Extract from Canarium odontophyllum Miq. Leaf in Combination with Oxacillin against Methicillin-Resistant Staphylococcus aureus (MRSA) ATCC 33591 Dayang Fredalina Basri and Vimashiinee Sandra School of Diagnostic & Applied Health Sciences, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia Correspondence should be addressed to Dayang Fredalina Basri; dayang@ukm.edu.my Received 13 November 2015; Revised 28 January 2016; Accepted 7 February 2016 Academic Editor: Barbara H. Iglewski Copyright © 2016 D. F. Basri and V. Sandra. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Canarium odontophyllum (CO) Miq. has been considered as one of the most sought-afer plant species in Sarawak, Malaysia, due to its nutritional and pharmacological benefts. Tis study aimed to evaluate the pharmacodynamic interaction of crude methanol and acetone extracts from CO leaves in combination with oxacillin, vancomycin, and linezolid, respectively, against MRSA ATCC 33591 as preliminary study has reported its potential antistaphylococcal activity. Te broth microdilution assay revealed that both methanol and acetone extracts were bactericidal with Minimum Inhibitory Concentration (MIC) of 312.5 g/mL and 156.25 g/mL and Minimum Bactericidal Concentration (MBC) of 625 g/mL and 312.5 g/mL, respectively. Fractional Inhibitory Concentration (FIC) indices were obtained via the chequerboard dilution assay where methanol extract-oxacillin, acetone extract-oxacillin, methanol extract-linezolid, and acetone extract-linezolid combinations exhibited synergism (FIC index ≤ 0.5). Te synergistic action of the methanol extract-oxacillin combination was verifed by time-kill analysis where bactericidal efect was observed at concentration of 1/8 × MIC of both compounds at 9.6h compared to oxacillin alone. As such, these fndings postulated that both extracts exert their anti-MRSA mechanism of action similar to that of vancomycin and provide evidence that the leaves of C. odontophyllum have the potential to be developed into antistaphylococcal agents. 1. Introduction MRSA has been a major cause of community, endemic, and epidemic nosocomial infections [1]. MRSA infections cause a range of illnesses, from skin and wound infection to pneumonia and blood stream infections that can cause sepsis and death. Te pathogen poses a huge threat as it has started to show resistance towards the last line of antibiotic treatment for Gram-positive bacteria [2–5] with vancomycin-resistant S. aureus [6] and linezolid-resistant S. aureus (LRSA) strains being reported worldwide [7]. Natural products, especially plants, have always been a great source of biological compounds for medicinal purposes [8]. Plants and their secondary metabolites ofer a diverse reservoir of bio- logically active components as potentially therapeutic agents, including antimicrobials [9]. Tese compounds are naturally present to protect plants from microorganisms, insects, and herbivores as well as giving plants their odour and pigments. Studies have revealed that many medicinal plant species from around the world can provide alternatives for a wide range of bacterial infections [10]. Canarium odontophyllum Miq., locally known as “dabai,” is a very popular fruit in Sarawak, largely consumed by the locals during its season. It is native to the tropical rainforest of Borneo and is reported as one of the underutilised fruits of Sarawak. Te CO fruit is rich in unsaturated fatty acids and contains sixteen types of phenolic compounds as well as exhibiting great potential as antioxidant [11–13]. Preliminary screening [14, 15] of methanol and acetone extracts of CO leaves showed antimicrobial activity towards Staphylococcus aureus and MRSA. Hindawi Publishing Corporation International Journal of Microbiology Volume 2016, Article ID 5249534, 7 pages http://dx.doi.org/10.1155/2016/5249534