Assessment of Antistaphylococcal Activity of Partially Purified Fractions and Pure Compounds from Eleutherine americana

Abstract

Ready-to-eat foods were investigated for contamination with methicillin-resistant Staphylococcus aureus (MRSA), and the partially purified fractions from the bulb of Eleutherine americana were evaluated for their anti-MRSA activity. Partially purified fractions Ea6.3 and Ea9 demonstrated good antibacterial activity with a MIC of 125 to 500 μg/ml and MBC of 250 to ≥1,000 μg/ml against all the food isolates. Fraction Ea6.3 produced a MIC and MBC of 250 and 500 μg/ml, respectively, whereas fraction Ea9 yielded MIC and MBC of 125 and ≥1,000 μg/ml, respectively, against the enterotoxin-producing reference strains. Growth curves in the presence of fraction Ea6.3 at 4× MIC resulted in total elimination of all the test strains between 20 and 24 h, while fraction Ea9 reduced bacterial population by at least 6 log relative to the control. The partially purified fractions were further purified to obtain pure compounds identified as eleutherol, eleutherin, isoeleutherin, hongconin, two anthraquinones, and elecanacin. The antibacterial activities of these compounds were also investigated; they produced MICs ranging from 31.25 to ≥1,000 μg/ml. This study suggests that E. americana crude extract or its partially purified fractions have potentials for application as natural food preservatives.