Abstract
The antibiotic resistant threat is continuing to grow, due in part to the overuse of antibiotics in livestock feed. Many nations in Europe have banned the use of antibiotics in feed, leading to higher rates of infection in livestock animals and reduced productivity for the food market. Increasingly, researchers are looking into the efficacy of phytopreparations to replace antibiotics in feed, allowing for increased animal health without the development of resistance. Macleaya cordata, or Chinese plume poppy, shows promise as a food additive. To evaluate the antimicrobial efficacy of this plant, we tested in vitro activity of M. cordata extract, as well as pure compounds sanguinarine and chelerythrine against wild-type, methicillin-resistant, and multiply-resistant strains of Staphylococcus aureus (SA1199, AH1263, and IA116, respectively). Combination tests to evaluate synergy, additivity, and antagonism within the extract were also completed for the first time. Sanguinarine and chelerythrine showed complete growth inhibition of all strains of S. aureus at concentrations ranging from 3-10 µg/mL, and were equal in activity or were more potent than the reference compound chloramphenicol. Combination studies of pure sanguinarine and chelerythrine with M. cordata extract revealed additivity or indifference of mixture components with these compounds. Because sanguinarine and chelerythrine represent the major active constituents of M. cordata, the pooled amounts of these two compounds may be useful for establishing potency for quality control purposes. This is the first report of activity of chelerythrine and sanguinarine against methicillin-resistant S. aureus AH1263 and multiply-resistant S. aureus IA116, and illustrates the promise of M. cordata extract as an alternative to antibiotics in feed additives.