Time-kill assay and post-antibiotic effect of acetone extract from the stem bark of Canarium odontophyllum against Methicillin-resistant Staphylococcus aureus Mu50 strain

Abstract

Canarium odontophyllum Miq. is an indigenous fruit found in Sarawak, Malaysia. Methicillin-resistant Staphylococcus aureus (MRSA) is a deadly pathogen that causes to hospital (health-care-acquired MRSA [HA-MRSA]) and community (CA-MRSA) infections worldwide. Vancomycin has been the therapeutic drug of choice against MRSA, but unfortunately this pathogen has developed some degree of resistance to vancomycin. This research aimed to evaluate the antimicrobial activity of the stem bark extract of C. odontophyllum against MRSA Mu50 strain. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of extract and vancomycin against MRSA were determined using broth microdilution method and streak plate method. The rate of killing by the extract against Mu50 strain was determined using time-kill assay (TKA) at ×1 MIC, ×2 MIC, ×4 MIC, and ×8 MIC of the extract. The post-antibiotic effect (PAE) time of extract ×10 MIC against MRSA was also investigated. The extract exhibited bacteriostatic effect against MRSA Mu50 strain with MIC and MBC values of 1.563 mg/ml and 3.125 mg/ml, respectively. From TKA analysis, the extract was not capable of killing the Mu50 strain at ×1 MIC and ×2 MIC, but it displayed bactericidal activity at higher concentrations tested. Interestingly, the acetone stem bark extract of C. odontophyllum at ×4 MIC showed comparable time-killing kinetic with the standard antibiotic in the study. The PAE time of the extract was 3.6 ± 0.51 h against MRSA Mu50 compared to vancomycin at 2.4 ± 0.68 h. In conclusion, the stem bark acetone extract from C. odontophyllum demonstrated concentration-dependent bactericidal effect with prolonged PAE time against MRSA Mu50 strain.