Microbiological and biochemical origins of human foot malodour

Abstract

Although foot malodour is a common consumer problem, the range of products available to combat the condition is fairly limited. In part, this is due to an incomplete understanding of how the key odorants are generated by microorganisms resident on the skin. The aim of these studies was to identify the key chemical components of foot malodour, the organisms and metabolic pathways responsible for their production, and to develop model systems to study these processes in vitro. Using gas chromatography with simultaneous mass spectrometry and sniff port detection, volatile fatty acids were implicated as foot malodorants, with isovaleric acid particularly prominent. l-Leucine was identified as the likely substrate, and the source of this branched amino acid postulated to be the degradation of foot callus. An in vitro assay was employed to screen a library of isolated foot bacteria for their ability to generate isovaleric acid from l-leucine. Staphylococcus species were found to be the main producers, while some Brevibacterium, Micrococcus and Kytococcus isolates fully catabolized isovaleric acid and l-leucine, indicating the dynamic nature of odour production. The degradation of foot callus by Kytococcus sedentarius was investigated, and an in vitro 'foot malodour model' developed, demonstrating the generation of isovaleric acid using a combination of partially purified K. sedentarius keratinases and a Staphylococcus species. The results of these studies provide new understanding on the microbiological and biochemical origins of foot malodour which, in turn, should lead to the development of novel deodorant systems for this part of the body. © 2012 John Wiley & Sons, Ltd.