Fatty acids of dermatophytes

The dermatophytes

The etiologic agents of the dermatophytoses (ringworm) are classified in three anamorphic (asexual or imperfect) genera, Epidermophyton, Microsporum, and Trichophyton. Species capable of reproducing sexually belong in the teleomorphic genus, Arthroderma, of the Ascomycota. On the basis of primary habitat association, they may be grouped as geophilic (soil associated), zoophilic, and anthropophilic. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics. The dermatophytes have the ability to invade keratinized tissue (skin, hair, and nails) but are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate viable tissue of an immunocompetent host. However, invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, keratinases, and other proteinases reportedly act as virulence factors. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection. Chronic dermatophytosis is mostly caused by Trichophyton rubrum, and there is some evidence that mannan produced by this fungus suppresses or diminishes the inflammatory response. Since dermatophytes cause a communicable disease, modes of transmission and control are discussed as well as a survey of recent trends in therapy. Collection of specimens, culture media, and tests for identification are also presented. Genetic studies have led to an understanding of incompatibility mechanisms, pleomorphism and variation, resistance to griseofulvin, and virulence. Molecular biology has contributed to our knowledge of the taxonomy and phylogenetic relationships of dermatophytes.

Fungitoxicity of fatty acids against dermatophytes

Ten saturated and three unsaturated fatty acids over a wide spectrum of their carbon chain length were tested for their fungitoxicity against five dermatophytes. The experiments showed that short chain saturated fatty acids (C 7:0-C 11:0) are more toxic to dermatophytes than long chain ones (> C 12:0). The antifungal activity decreases with increasing carbon chain length in the even-numbered carbon chain series. Odd-numbered carbon fatty acids show irregularities in these respects. Undecanoic acid (C 11:0) is outstandingly most toxic in the C 7:0-C 18:0 series. Polyunsaturated fatty acids are more toxic than their corresponding saturated acids. The per cent growth inhibition decreased from day 4 to day 12 at all concentrations suggesting the degradation and/or utilization of fatty acids by the fungi during the observation period. The results are discussed on the background of the biochemistry of fatty acids.

Effect of keratin on the lipid composition of Scopulariopsis brevicaulis (Bainier)

Lipid content and composition of Scopulariopsis brevicaulis cultured with or without its natural substrate keratin was investigated. Lipid content was found to be lower in the presence of keratin (maximum 12% against 19% in the absence of keratin), with differences in levels of linoleic acid (C18 = 2), palmitic (C16:0) and to a lesser extent palmitoleic (C16 = 1) and alpha-linolenic (C18 = 3) acids. The degree of unsaturation was correspondingly lower in the organisms cultured with keratin as substrate.

Antigenic characterization of Microsporum canis, M. distortum, M. equinum, M. ferrugineum and Trichophyton soudanense cultures

The authors investigated the antigenic properties of a group of closely related dermatophytes whose components may be morphologically confused with one another: Microsporum canis, M. distortum, M. equinum, M. ferrugineum and Trichophyton soudanense. By using reference antigens and adsorbed monospecific antisera, it was possible to serologically distinguish the reference strains by the exoantigen technique. Their common and specific antigenic determinants were visualized by cross-immunoelectrophoresis tests with intermediate gel.

Lipids of dermatophytes II. Effect of growth condition on the lipid composition and membrane transport of Microsporum gypseum

Supplementation of glucose-containing medium with ethanol and replacement of glucose by glycerol in the Sabouraud's growth medium of Microsporum gypseum altered the levels of total phospholipids as well as their apolar and polar head groups. The levels of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) increased under these growth conditions; also, the ratio of unsaturated/saturated phospholipid fatty acids decreased on ethanol supplementation but increased in the presence of glycerol. Steady state accumulation of labelled amino acids (glycine, lysine and aspartic acid) was affected under these conditions.

Scanning electron microscopy on Microsporum audouini complex

Several strains of Microsporum audouini, M. langeroni and M. rivalieri were observed by light and scanning electron microscopies. The macroaleuriospore shape and ornamentation were illustrated and compared for the 3 species as the pectinate hyphae for M. langeroni and M. rivalieri and the chlamydospores and particular hyphae for M. audouini and M. langeroni. The 3 species are morphologically very close but they are distinguishable from each other on the basis of morphology, geographic distribution and pathogenicity.