Antistaphylococcal activity of semi-purified fractions from Eleutherine americana

Abstract number: P580

Voravuthikunchai S., Ifesan B.O.T., Mahabusarakam W., Hamtasin C.

Introduction: Meticillin-resistant Staphylococcus aureus (MRSA) infections are a global health concern due to the severity of the illnesses they may cause, ranging from mild to very severe infections. The numbers of S. aureus strains that exhibit antimicrobial resistance properties have increased and there is a potential risk of transmitting antibiotic resistance genes to the human microbiota through foods. Interest in plants with antibacterial properties has revived as a consequence of current problems associated with the use of antibiotics. Preliminary research from our laboratory revealed that the crude extract from Eleutherine americana produced good antibacterial effect on S. aureus from foods. The aim of the present study was to examine the activity of semi-purified fractions from this plant extract against meticillin-resistant strains isolated from foods and enterotoxin-producing reference strains.

Methods: Twenty-two MRSA strains isolated from food together with two enterotoxin-producing strains (ATCC 23235 and ATCC 27664) were used in this study. The Minimum inhibitory concentration (MIC) was determined by the broth dilution method and Minimum bactericidal concentration (MBC) was performed with the extracts that gave significant MIC values using a sterile loop streaking on fresh MHA (CLSI standard methods). Time-kill assay in the presence of these fractions were carried out. The crude hexane extract was chromatographed on column chromatography and fractions were obtained on the basis of their TLC characteristics.

Results: Fraction Ea 6.3 had MIC90 of 0.25 mg/ml while Ea 9.0 gave MIC50 of 0.125 mg/ml with MBC values ranging from 0.25 1.00 mg/ml for the two fractions on all the strains tested. Kill-curve in the presence of Ea 6.3 at 4MIC resulted in total killing of the cells at 20 h for reference strains and 24h for MRSA while fraction Ea 9.0 reduced the inoculum size by 7 log cycle.

Conclusion: Both fractions were very effective against all food isolated MRSA as well as enterotoxin-producing strains. These semi-purified fractions are being investigated in our laboratory to provide alternate treatment against MRSA.

Acknowledgements: Supported by Graduate School Prince of Songkla University and Thailand Research

Fund (BRG 4880021, fiscal year 2005–2008).