Antibacterial Activity of Retinaldehyde against <i>Propionibacterium acnes</i>

Abstract

<b>Background:</b> Retinaldehyde has been shown to exert antibacterial activity in vitro. <b>Aim:</b> This study evaluates the effect of retinaldehyde on <i>Propionibacterium acnes</i> both in vivo and in vitro. <b>Methods:</b> Microbial minimal inhibitory concentrations (MICs) of retinaldehyde and retinoic acid were determined on reference strains of <i>P. acnes.</i> In vivo activity of daily topical application of 0.05% retinaldehyde on the <i>P. acnes</i> density was evaluated after application in a single-blind randomised study. <b>Results:</b> MICs of retinaldehyde were 4 mg/l for <i>P. acnes</i> No. CIP179 and CIP53119 and 8 mg/l for <i>P. acnes</i> No. CIP53117. In contrast, the MICs of retinoic acid were superior to 128 mg/l for these three strains. In vivo, retinaldehyde-treated areas displayed a significant decrease in counts of viable <i>P. acnes</i> as compared with the untreated areas with a median decrease of 10<sup>2</sup> log <i>P. acnes</i>/cm<sup>2</sup> after 2 weeks of daily application. Vehicle alone had no effect. <b>Conclusion:</b> The MIC of retinaldehyde against <i>P. acnes</i> suggests a direct antibacterial activity. Daily topical application of 0.05% retinaldehyde is associated with a clear reduction of the <i>P. acnes</i> density.