Brief communication: extracellular enzymatic activities of dermatophytes

The host range of dermatophytes, it is at all possible? Phenotypic evaluation of the keratinolytic activity of Trichophyton verrucosum clinical isolates

Dermatophytes are fungi that have an ability to invade keratinised structures. Enzymes secreted by dermatophytes can underlie fungal survival on the host and development of infection. It is possible that the range of activity of keratinases from various dermatophytes is limited to specific species of animals and groups of people. The aim of this study was to carry out phenotypic analysis of the degree of keratinolytic activity of Trichophyton verrucosum strains using hairs of humans and various animal species as substrates. Our results indicated that the activity of keratinases is substrate-induced. The host range of T. verrucosum can be defined as wide. The highest activity of keratinases was recorded in media containing keratin from cow (Bos taurus) and sheep (Ovis aries) hairs in comparison with that from other tested species. The production of keratin-degrading enzymes is a function of time, with the peak of their activity occurring on day 15 of incubation. The role of keratin-degrading enzymes in the pathogenesis of dermatophytosis is becoming increasingly clearer. Given the conceptual understanding that keratin breakdown may require more than just one enzyme, the use of phenotypic methods is an optimal approach to in vitro study of the decomposition of species-specific keratin.

Extracellular enzymatic activity of Microsporum canis isolates

The enzymatic activity of 70 feline and canine Microsporum canis isolates was determined by the Api-Zym test. The liquid phase of cultures, inoculated into Tryptic Soy Broth, was used to examine 19 enzymes. Considerable differences were observed among the extracellular enzymatic patterns. All the isolates produced alkaline phosphatase and beta-glucosidase, while lipase (C14), trypsin, chymotrypsin, beta-glucuronidase, and alpha-fucosidase activity was never revealed. Esterase (C4) activity was present in 57 samples (81%), esterase lipase (C8) in 31 (44%), leucine arylamidase in 35 (50%), valine arylamidase and cystine arylamidase in 7 (10%), acid phosphatase in 64 (91%), naphthol-AS-BI-phosphohydrolase in 60 (86%), alpha-galactosidase in 5 (7%), beta-galactosidase in 6 (8%), alpha-glucosidase in 25 (36%), N-acetyl-beta-glucosaminidase in 41 (58%), and alpha-mannosidase in 51 (73%). The beta-galactosidase activity of M. canis has not been reported previously. Remarkable variations of intensity for each enzymatic activity were also detected. It is believed that these results could provide basic data for further investigations on the pathogenic role of enzymes secreted by M. canis.

Enzyme patterns of dermatophytes

Exoenzymes produced by common dermatophytes, in addition to their ability to cause cutaneous inflammation, are thought to contribute to fungal spread. To investigate the patterns of enzymes released by common dermatophytes as well as Scopulariopsis brevicaulis, the fungi were grown in liquid media containing either hair, stratum corneum, neopeptone or lipids, or in RPMI medium. Enzymes recovered from the culture supernatants were compared using the Api-zyme test. As a result, the widest range of enzymes was seen in protein-containing media, with a maximum of 13 enzymes stimulated by growth on hair. Dermatophytes in all protein media produced high levels of alkaline phosphatase, esterases and leucine arylamidase. In these media the highest total enzymatic activity was released by Microsporum canis, whereas the lowest was released by Epidermophyton floccosum. Although RPMI broth stimulated luxuriant growth of all species, recovery was limited to a maximum of six enzymes. In lipid medium E. floccosum and M. canis failed to grow. When comparing the various nutrients, Scopulariopsis released fewer enzymes than the dermatophytes and only minor quantities of alkaline phosphatase. We conclude that alkaline phosphatase, esterases and leucine arylamidase may be important for the parasitic growth of dermatophytes. The total enzymatic activity of dermatophytes appears to be correlated with the intensity of cutaneous inflammation. Furthermore, enzyme measurements may be helpful for species identification.

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.

Enzyme release by Trichophyton rubrum depends on nutritional conditions

Enzymes liberated by growing dermatophytes are of pathogenetic importance in tinea. To investigate the influence of nutrients on this enzyme release, Trichophyton rubrum was grown in media containing peptone, keratin and lipids, to which glucose was added in separate assays. The culture supernatants were compared for extracellular enzyme activities by use of the api-zym test. Our results clearly show that the extracellular enzyme activity is dependent on the nutrients supplied. Seven different enzymes were released when keratin was supplied, as compared with only five and two respectively when lipids or peptone were available. Among these enzymes alkaline phosphatase and N-acetyl-beta-glucosaminidase were detected in all cultures lacking glucose. Enzyme release was inhibited completely when glucose was added to the media, except for N-acetyl-beta-glucosaminidase in peptone cultures. This dependency of enzyme release on fungal nutrition can be expected to occur in vivo too. In addition, it has to be considered for in vitro cultural conditions. Alkaline phosphatase and acetylglucosaminidase may be more important in tinea than has been assumed so far.