ORIGINAL ARTICLE Inhibition of growth of Trichophyton tonsurans by Lactobacillus reuteri J. Guo 1 , A. Mauch 2 , S. Galle 2 , P. Murphy 1 , E.K. Arendt 2 and A. Coffey 1 1 Department of Biological Sciences, Cork Institute of Technology, Bishopstown, Cork, Ireland 2 Department of Food Science, Food Technology and Nutrition, National University of Ireland, Cork, Ireland Introduction Fungal infection of the skin is a common global problem. Currently, 20–25% of the world’s population suffers from skin mycosis, making these one of the most frequent forms of infection (Havlickova et al. 2008). Tinea capitis is a fungal infection involving the hair shaft of the scalp. It is commonly referred to as ringworm and occurs primarily in children. Since the 1950s, Trichophyton tonsurans has emerged from Mexico and the Caribbean and is now the most prevalent cause of tinea capitis in North America (Shroba et al. 2009) and the UK (Fuller 2009). Trichophyton tonsurans is frequently resistant to traditional fungicides (Me ´ndez-Tovar et al. 2007; Coelho et al. 2008; Manzano-Gayosso et al. 2008). Antifungals normally used belong to two classes namely polyene anti- fungals and azole antifungals. The polyene antimycotics bind with sterols in the fungal cell membrane, principally ergosterol. As a result, the cell’s contents leak resulting in cell death. Animal cells contain cholesterol instead of ergosterol and so they are much less susceptible. As a polyene’s hydrophobic chain is shortened, its sterol binding activity is increased. Therefore, further reduction in the hydrophobic chain may result in it binding to cholesterol, making it toxic to animals (Baginski and Czub 2009). The azole antifungals such as imidazole and triazole drugs are synthetic agents that inhibit the enzyme cytochrome P450 14a-demethylase. This enzyme converts lanosterol to ergosterol and is necessary for fungal cell membrane synthesis. These drugs also block steroid Keywords antifungal, dermatophyte, Lactobacillus reuteri, tinea capitis, Trichophyton tonsurans. Correspondence Aidan Coffey, Department of Biological Sciences, Cork Institute of Technology, Bishopstown, Cork, Ireland. E-mail: aidan.coffey@cit.ie 2011 / 0112: received 19 January 2011, revised 4 April 2011 and accepted 5 April 2011 doi:10.1111/j.1365-2672.2011.05032.x Abstract Aim: The aims of this study were to identify antifungal lactic acid bacteria (LAB) and characterize their activity against the dermatophyte Trichophyton tonsurans. Methods and Results: A total of 165 different LAB were isolated and initially screened for anti-Penicillium expansum activity. Five strains, which exhibited strong inhibitory activity, were then tested against the dermatophyte T. tonsu- rans DSM12285, where they also caused inhibition as observed by large fungal clearing on agar surface. The strongest inhibition was seen with Lactobacillus reuteri R2. When freeze-dried cell-free supernatant powder from this strain was incorporated in culture medium at concentrations >1%, growth of fungal col- ony was inhibited. Conidia germination was also inhibited under these condi- tions as determined by microscopy. The anti-T. tonsurans activity of Lact. reuteri R2 was not affected neither by heat treatment nor by proteolytic treatment using pronase E and proteinase K, indicating that the responsible agent(s) were nonproteinaceous in nature. Conclusions: Lactobacillus reuteri R2 was identified as having strong inhibitory activity against the dermatophyte T. tonsurans DSMZ12285. Significance and Impact of the Study: LAB are naturally associated with many foods and are well recognized for their biopreservative properties. The use of these and / or their products may well provide alternative safe approaches for the inhibition of dermatophytic fungi. Journal of Applied Microbiology ISSN 1364-5072 474 Journal of Applied Microbiology 111, 474–483 ª 2011 The Society for Applied Microbiology ª 2011 The Authors