Honeys with non-peroxide antimicrobial activity are more closely associated with floral source, being generally derived from Leptospermum species [8], [9], although this type of activity has also been found in a small number of non-Leptospermum honeys [9], [17], [18], [19]. In a clinical setting where honey is used as a topical antimicrobial and wound dressing, non-peroxide activity may be advantageous as it is not destroyed by catalase present in body fluids, and is unaffected by gamma irradiation [20], allowing these honeys to be sterilized for medicinal use. The compound primarily responsible for non-peroxide activity in New Zealand manuka honey has recently been identified as methylglyoxal (MG) [21], [22], which is derived from dihydroxyacetone, a compound present in high levels in manuka nectar [23]. The reasons for varying dihydroxyacetone levels in different plants are not yet understood.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065476/#pone.0018229-Henriques1