227 Effect of triamcinolone & manuka honey on Staphylococcus aureus growth & hemolytic activity

Abstract

Atopic dermatitis (AD) is an inflammatory skin disease commonly treated with topical corticosteroids (TCS). Manuka honey (MH) is an alternative therapy made from nectar of the Leptospermum scoparium, native to New Zealand. The high abundance of Staphyloccocus aureus (S. aureus) on AD skin enhances disease severity, in part due to the effects of hemolysins. To address the effect TCS & MH have on S. aureus, we quantified growth & hemolytic activity of USA300 (MRSA strain) with & without exposure to triamcinolone acetonide (TAC) or MH. USA300 was cultured in Tryptic soy broth (TSB) containing 0.1% w/v TAC or MH (ManukoraTM; 1.25%, 2.5%, 5% & 10% w/v). Growth after MH exposure was evaluated by measuring optical density at 600nm (OD600). Due to TAC’s low solubility which interfered with OD readings, we evaluated growth by colony forming units (CFUs) after 5 hrs. After 24 hrs, supernatants were filtered (0.22-μm) and spotted onto rabbit blood agar (RBA) to quantify hemolytic activity (diameter of zones of clearance). TAC exposure resulted in a slightly lower CFUs (avg 0.82 x 109) than TSB alone (avg 1.26 x 109 CFU; n=2/condition), suggesting that TAC did not significantly inhibit USA300 growth. In contrast, MH markedly reduced OD600 values by 5, 23, 82 & 92% in 1.25, 2.5, 5, & 10% MH, respectively, compared to TSB alone (mean; n=3, p<0.03) after 5 hrs. This inhibitory effect of MH on USA300 growth was notable with the most significant reduction (mean 35%; n=3, p=0.001) observed at the highest concentration (10%) that was still observed at 24 hrs. Supernatants from TAC-incubated USA300 reduced clearance zones on RBA (avg 1.8±0.4 mm) compared to TSB alone (avg 5.8±0.4 mm; n=2/condition). Whereas, MH, inhibited all hemolytic activity, even at the lowest concentration 1.25% (n=3). Collectively, these findings demonstrate that at even at low MH concentrations, commonly found in cosmetic products, there is a greater effect on S. aureus growth as well as nearly complete inhibition of hemolytic activity compared to TAC, the most commonly used topical TCS.