Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is a deadly pathogen that initially was limited to hospital and healthcare facilities but has gradually became a growing problem in healthy children and adults. Pterostilbene belongs to the phenylpropanoid phytoalexin which is involved in plant response to various pathogen and herbivores attack. The aim of this study is to evaluate the anti-MRSA action of pterostilbene in combination with selected antibiotics; vancomycin, linezolid and oxacillin against ATCC 43300 and ATCC 33591. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and fractional inhibitory concentration (FIC) index values were determined. Microbroth dilution technique and microdilution checkerboard (MDC) assay were employed. The MIC and MBC of pterostilbene against ATCC 33591 was 31.25 and 62.50 µg mL-1, respectively. While for ATCC 43300, the MBC value was also twice (62.50 µg mL-1) its MIC value of 31.25 µg mL-1. This indicated that pterostilbene was bacteriostatic against both MRSA strains. Our MIC/MBC study also showed that linezolid exhibited bacteriostatic action but, oxacillin and vancomycin were bactericidal. MDC study showed that pterostilbene-oxacillin combination exhibited lowest FIC value (0.56) against both MRSA strains which indicated partial synergistic interaction. On the other hand, pterostilbene was additive (FIC 1.00) in combination with vancomycin whereas pterostilbene-linezolid combination displayed indifference effect with FIC of 1.25 against both MRSA strains. Pterostilbene in combination with oxacillin partially enhanced anti-MRSA activity with twofold reduction in MIC of oxacillin by acting at different site at the bacterial cell wall from that of oxacillin but more specific to the site of action of vancomycin.
Highlights
Methicillin-resistant Staphylococcus aureus (MRSA) is a human pathogen that causes both nosocomial and community-acquired infection (Boucher et al, 2010; Grundmann et al, 2006; McCarthy et al, 2010)
American Type Culture Collection (ATCC) 43300 strain was more susceptible to the effect of vancomycin and oxacillin at minimum inhibitory concentration (MIC) values of respectively, 0.49 and 31.25 μg mL−1
From the minimum bactericidal concentration (MBC) values of vancomycin and oxacillin, it can be seen from Table 3 and 4 that both antibiotics were bactericidal against MRSA
Summary
Methicillin-resistant Staphylococcus aureus (MRSA) is a human pathogen that causes both nosocomial and community-acquired infection (Boucher et al, 2010; Grundmann et al, 2006; McCarthy et al, 2010). The emergence of MRSA which has caused an increase in incidence and prevalence rate in many country, is widely known for causing endocarditis, meningitis, bacteremia, osteomyelitis and toxic shock syndrome (Lowy, 2003). In addition to its parental indication, the side effects associated with vancomycin are nephrotoxicity, hearing impairment and ‘red man syndrome’. The latter is known to cause skin redness and itching resulting from histamine reaction (Alexander and Greenberger, 1996). To complicate the situation, uncontrolled spreading of MRSA and the increased usage of vancomycin make the drug more susceptible to failure due to emergence of vancomycin-resistant organism (Hiramatsu, 2001)
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