Fatty acid metabolism by cutaneous bacteria and its role in axillary malodour

Abstract

It is generally accepted that short (C₂-C₅) and medium (C₆-C₁₁) chain volatile fatty acids (VFAs) are among the primary causal molecules of axillary malodour. It is also widely acknowledged that malodour generation is attributable to the biotransformation of odourless natural secretions, into volatile odorous products, by cutaneous bacteria. However, little information is available on the biochemical origins of VFAs on axillary skin. In these studies, assay systems were developed to investigate the generation of VFAs from lipid substrates readily available to the bacteria resident on axillary skin. A major route to short and medium chain VFAs in the axilla was shown to be the partial catabolism of structurally unusual (e.g. methyl-branched) longer chain fatty acids by a previously uncharacterized sub-group of the Corynebacterium genus, corynebacteria (A). In contrast, corynebacteria (B) are incapable of growth on fatty acid. Structurally unusual fatty acids originate from the triacylglycerol component of sebum, and probably also apocrine sweat, by the action of bacterial lipases. Interestingly, VFA formation in the axilla is a dynamic process, with some cutaneous microorganisms, specifically micrococci and brevibacteria, capable of fully catabolizing these odorants. The results of these studies provide new understanding on the biochemical origins of VFA-based axillary malodour.