Comparison of Disk Diffusion and Micro-Dilution Broth Methods for Evaluation of Antimicrobial Effects of Myrtus Extract on Methicillin-Resistant Staphylococcus Aureus and Escherichia Coli ESBL

In this study, the effect of Myrtus extracts on 25 methicillin resistant Staphylococcus aureus (MRSA) and Escherichia coli ESBL strains isolated from patients were compared by two methods.

15 methicillin-resistant Staphylococcus aureus (MRSA) and 10 Escherichia coli ESBL isolates were used in this study. Fresh Leaves of Myrtus were collected from the herbal medicine farm. Extraction was performed using a reflux distillation. The effect of concentrations 0.195-100 micrograms per ml of Myrtus extract on clinical isolates was analyzed in disk diffusion method compared with micro broth dilution method and with MTT in 545 nm on an ELISA reader apparatus.
Findings: Inhibition zone diameter for the minimum effective concentration of 50 micrograms per milliliter in all isolates of ESBL and MRSA were as 8±1 mm and 11±1. Minimum Inhibitory Concentration (MIC) was 6.25mic/ml and Minimum Bactericidal Concentration (MBC) was determined 12.5mic/ml for E. coli ESBL. Furthermore, the amounts for MIC and MBC was determined as 12.5 and 25 mic/ml, respectively for Staphylococcus aureus.

The results of this study showed compliance of two methods in evaluation of drug-resistant clinical isolates. It was proved that the disk diffusion method could be determining range of effective concentration but micro broth method determines the effective concentration carefully. It is recommended that results obtained from disk diffusion not to be basis for final decisions in traditional medicine studies. Bacterial behavior in the broth and determination of the point of death greatly increases the accuracy of the results.