The MRJP1 honey glycoprotein does not contribute to the overall antibacterial activity of natural honey

Abstract

A recent study has claimed that honey glycoproteins including major royal jelly protein 1 (MRJP1), the most abundant protein in honey, exhibit strong antibacterial activity at μg/ml concentrations. These were shown to be effective against a broad spectrum of multidrug-resistant clinical isolates. In this study, we investigated the antibacterial activity of the protein content of three different sterile honey samples (manuka honey, Revamil source honey and honeydew honey) used in wound care, and characterised the antibacterial activity of purified MRJP1. Following ultrafiltration, honey samples contained different amounts of proteins. The most abundant protein was MRJP1. Honey proteins with a molecular weight (MW) above 10 kDa did not inhibit the growth of the laboratory strain Micrococcus luteus. Similarly, purified MRJP1 did not possess any antibacterial activity against M. luteus, Pseudomonas aeruginosa and Staphylococcus aureus in both an agar well diffusion assay and a broth microdilution assay. The results of this study indicate that honey proteins with a MW above 10 kDa, including MRJP1, do not possess direct antibacterial activity.