Proteolytic activity of dermatophytes and its role in the pathogenesis of skin lesions

Fungal contamination of poultry litter: a public health problem

Although numerous studies have been conducted on microbial contaminants associated with various stages related to poultry and meat products processing, only a few reported on fungal contamination of poultry litter. The goals of this study were to (1) characterize litter fungal contamination and (2) report the incidence of keratinophilic and toxigenic fungi presence. Seven fresh and 14 aged litter samples were collected from 7 poultry farms. In addition, 27 air samples of 25 litters were also collected through impaction method, and after laboratory processing and incubation of collected samples, quantitative colony-forming units (CFU/m³) and qualitative results were obtained. Twelve different fungal species were detected in fresh litter and Penicillium was the most frequent genus found (59.9%), followed by Alternaria (17.8%), Cladosporium (7.1%), and Aspergillus (5.7%). With respect to aged litter, 19 different fungal species were detected, with Penicillium sp. the most frequently isolated (42.3%), followed by Scopulariopsis sp. (38.3%), Trichosporon sp. (8.8%), and Aspergillus sp. (5.5%). A significant positive correlation was found between litter fungal contamination (CFU/g) and air fungal contamination (CFU/m³). Litter fungal quantification and species identification have important implications in the evaluation of potential adverse health risks to exposed workers and animals. Spreading of poultry litter in agricultural fields is a potential public health concern, since keratinophilic (Scopulariopsis and Fusarium genus) as well as toxigenic fungi (Aspergillus, Fusarium, and Penicillium genus) were isolated.

Extracellular protease expression in Microsporum gypseum complex, its regulation and keratinolytic potential

Two soil isolates of Microsporum gypseum were studied for the production of extracellular proteases. Both the strains secreted protease on glucose-gelatin medium. The enzyme activity peaked on day 15 at 28 °C. Asparagine repressed protease yield. Sugars caused catabolite repression of protease formation. Protease activities of both the isolates were significantly affected by incubation period, culture media and carbohydrates used. Both the strains grew on the skin bait and caused a gravimetrically measurable loss of the substrate. Despite less pronounced differences in the keratinase levels, great variations occurred in the amount of keratin degraded by two isolates. Keratinase production as well as loss in substrate mass was better in glucose-lacking flasks than those containing the sugar. Although the rate of keratin degradation was independent of enzyme production, statistically positive correlations were recorded between loss in substrate mass: yielded dry mycelial weight and substrate degradation: keratinase levels.

Keratinophilic fungi of poultry farm and feather dumping soil in Tamil Nadu, India

Soils of 10 poultry farms from Namakkal and 12 feather dumping sites from Chennai were studied for the presence of keratinophilic fungi. A total of 34 species belonging to 19 genera and one non-sporulating fungus were recovered. Sixteen species of fungi and one non-sporulating fungi were common to both sites, eight species were specific to Namakkal and nine species were specific to Chennai. Dermatophytes and closely related fungi were represented by six species belonging to five genera. Fungal species commonly found in the soil samples included Chrysosporium keratinophilum (73%), Trichophyton mentagrophytes (68.2%), Microsporum gypseum (64%), Myceliopthora vellerea (32%), Chrysosporium state of Arthroderma tuberculatum (27.3%) and Geomyces pannorum (23%). Non-dermatophyte fungi were represented by 28 species belonging to 14 genera and one non-sporulating fungus.

Production of extracellular enzymes by Microsporum canis and their role in its virulence

Microsporum canis is the most prevalent dermatophyte of domestic animals. Several enzymes produced by dermatophytes, particularly keratinases, are considered to play a role in the virulence of this fungus. To investigate the possible relationship between the clinical status of M. canis infection and enzymatic activity of isolates, we studied the relationship between keratinase, elastase, lipase and DNase levels produced in vitro by different isolates and virulence as expressed in a guinea pig model. Samples isolated from symptomatic dogs and cats showed a statistically significantly (P < 0.05) higher keratinase activity than samples isolated from asymptomatic animals. Experimental infection of guinea pigs showed that a strain with high in vitro keratinase activity induced acute infection, which resolved clinically and mycologically faster than the infection induced by a strain with low keratinase activity. This suggested a strong correlation between high keratinase activity and the development of symptoms. The same correlation was not observed for other enzymes tested.

Production of proteinase and phospholipase by Paracoccidioides brasiliensis

We have investigated the production of proteinase and phospholipase by 20 different isolates of Paracoccidioides brasiliensis. Isolates were grown in Bacto-peptone, Dextrose, pH 5.5, agar slants, at 27 degrees C for 30 days, and cultures were transferred onto Petri dishes containing basis medium and bovine serum albumin fraction V and sterile egg yolk as substrates for enzyme production, and incubated at 27 degrees C. After 30 days net enzyme activity was visualized and quantitatively evaluated, measuring a ratio between colony diameter and diameter of the transparent (proteinase) or white (phospholipase) ring zone surrounding it. Results demonstrated that all isolates had the ability to produce proteinase and phospholipase, even though variability in enzyme production was noted among different isolates of P. brasiliensis.

Keratinolysis by poultry farm soil fungi

Species of Chrysosporium, Malbranchea, Scopulariopsis, Microascus, and Gliocladium isolated from poultry farm soils were grown on two keratin media. All the test fungi could grow on keratin (human hair) and degrade it, releasing sulphydryl-containing compounds detected as extracellular keratinase, cysteine and total proteins. Glucose supplemented keratin medium supported maximum keratinolysis. Keratinase activity also changed the pH of the medium towards alkalinity and species with strong keratinolytic ability were noted to render the culture medium more alkaline than those that were less kiratinolytic.

Partial purification and kinetic studies of exocellular proteinase from Trichophyton mentagrophytes var. erinacei

The dermatophyte Trichophyton mentagrophytes var. erinacei isolated from a patient with tinea cruris was cultured in peptone-glucose broth from which an exocellular proteinase was obtained. The enzyme was partly purified by Sephadex G-100 gel filtration. Its molecular weight was determined to be 33,000 on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimal pH was 8.5, the optimal temperature 35 degrees C. The proteolytic activity was specifically increased against casein and inhibited by phenylmethylsulphonyl fluoride. The enzyme was identified as alkaline serine proteinase.

Characterization of an extracellular keratinase of Trichophyton simii and its role in keratin degradation

The ability of Trichophyton simii HN 50, isolated from the Ghana Bird Sanctuary, Bharatpur, India, to produce extracellular keratinase was studied. Enzyme was produced on a keratin salt broth medium at pH7 and a temperature of 28 +/- 1 degree C. Enzyme secretion was best at 15 days of incubation. Asparagine and keratin were repressive to enzyme yield in comparison to gelatin. No relationship was observed between enzyme release and biomass sugars suppressed keratinase production in descending order as follows: glucose > mannose > maltose > arabinose > fructose. The enzyme showed ability to degrade all of the 3 keratin substrates. Buffalo skin was best degraded in the absence of glucose while chicken feathers were the least degraded in its presence.

Partial characterization of proteolytic enzymes of Microsporum canis and Microsporum cookei

Characterization by proteinase inhibitors of the enzymes produced by Microsporum spp. revealed that Microsporum canis and Microsporum cookei produce serine proteinase(s), but only M. canis expresses aspartic and cysteine proteinases and probably a metalloproteinase. Both M. canis and M. cookei expressed metalloelastinolytic proteinases. All the proteinase types have been implicated in the pathogenicity of a wide range of microorganisms.

Expression of PZ-peptidases by cultures of several pathogenic fungi. Purification and characterization of a collagenase from Trichophyton schoenleinii

Peptidolytic activity was studied in the broken-cell extracts of 17 isolates of pathogenic fungi tested with phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-Arg (PZ-PLGPA) as a substrate. All the fungi studied except Candida spp., Cryptococcus neoformans and two actinomycetes hydrolyzed the substrate and therefore contained a so-called PZ-peptidase activity. Of all the positive strains, Trichophyton schoenleinii, a pathogenic fungus showed the highest activity and was therefore chosen as a source for PZ-peptidase purification. The four chromatographic steps, a 'negative' dye column, a 'positive' dye column, hydroxyapatite Ultrogel, and modified TSK (HW 55), gave a highly purified peptidase with a 12% overall yield. Inhibitor studies suggested that the 82 000 M(r) PZ-peptidase is a metalloproteinase. Moreover it cleaved native rat type I collagen. Partial peptide sequencing showed a strong sequence homology to regions of two metalloproteinases previously identified in the yeast Saccharomyces cerevisiae and in rat.

Preparation of antigens from Trichophyton mentagrophytes using a new semi-solid culture medium and their characterization by SDS-PAGE and immunological techniques

A new semi-solid culture medium was developed by substituting the agar in Sabouraud glucose medium by Lutrol FC 127 (BASF, Ludwigshafen, Germany). This culture medium can be liquefied by cooling it down from the incubation temperature to 5-10 degrees C, thus allowing the full harvest of fungal mycelium without any contamination by the gelling agent for antigen preparation. More than 25 protein bands with molecular weights in the range of 98 to 12 kDa were fractionated by SDS-PAGE in antigen preparations from Trichophyton mentagrophytes. Hyperimmune antisera were raised in rabbits and used for immunological studies. Heat-inactivated mycelium was used for the absorption of antibodies against heat-stable cell wall constituents. This absorption facilitated the detection of specific protein bands during immunoblotting which revealed 17 protein antigen bands reacting with antibodies over a range of molecular weights from 98 to 24 kDa.

Keratinolysis by Absidia cylindrospora and Rhizomucor pusillus: biochemical proof

Absidia cylindrospora and Rhizomucor pusillus causal agents of phycomycoses, were cultured on sterile natural keratins in a mineral solution and the keratin degradation products analyzed. The excess of sulphur was removed by oxidation to inorganic sulphate and thiosulphate, which were the main products of sulphitolysis of keratin. The proteolytic activity of the two fungi depended on the nature of the keratin substrate. Human scalp hair was the most favoured keratin substrate by both the fungi.

The effect of dermatophyte species and density of infection on the pathology of ringworm

In this study we have measured the mean hyphal length as a function of the density of infection in skin surface biopsies from patients suffering from infection with different species of dermatophyte. The tissue response in the epidermis and dermis of these patients was evaluated for the degree of eczematization (epidermal thickening, spongiosis and dermal infiltrate) in periodic acid Schiff stained histological sections, employing visual analogue scales. There was no correlation between mean hyphal density and the degree of eczematization.

Regulation of Trichophyton rubrum proteolytic activity

Trichophyton rubrum is the most common dermatophyte of humans and normally colonizes the superficial layers of the epidermis (stratum corneum). Several proteinases with a possible role in the metabolism of host proteins have been purified from this fungus. The regulation of these enzymes and their role in fungal metabolism were studied at the biochemical level. General proteolytic (azocollytic) activity was repressed when log-phase cultures of T. rubrum were grown in a minimal medium that contained readily metabolized sources of carbon, nitrogen, sulfur, and phosphorus. When either carbon, nitrogen, or sulfur was deleted from this minimal medium, azocollytic activity was derepressed. In all cases a high-molecular-weight activity (Mr, greater than 200,000) was expressed. A 71,000-Mr proteinase was observed in nitrogen-depleted cultures, and proteolytic species of Mr 124,000 and 27,000 were secreted in sulfur-depleted cultures. The addition of either inorganic (MgSO4, Na2SO3, NaS2O3) or organic (methionine, cysteine) sulfur to the sulfur-depleted medium repressed the expression of azocollytic activity. In contrast, keratinolytic activity was not repressed by carbon, nitrogen, or sulfur but instead was induced when a protein source was included in the minimal medium. Stationary-phase cultures of T. rubrum secreted all proteolytic activities constitutively. Unlike log-phase cultures, the stationary-phase cultures secreted azocollytic, elastinolytic, and keratinolytic activity in minimal medium. These activities fell in the carbon-, nitrogen-, and phosphorous-depleted media but remained high in sulfur-depleted medium. The following model is proposed for the regulation of T. rubrum proteolytic activity. In the initial stages of infection, T. rubrum grows logarithmically. In this state, proteolytic activity is derepressed whenever carbon, nitrogen, or sulfur is lacking in the fungal milieu. The general proteinases produced would act on the nonkeratinous proteins in the stratum corneum. There are probably peptidases, as yet unidentified, that would cleave the peptides generated by the initial proteolysis into amino acids. These amino acids would provide the cell with a source of carbon, nitrogen, and sulfur. Under these conditions, the expression of general proteinases would be repressed, whereas specific keratinases would be induced in this nutrient-rich environment. Disease may occur when the fungus reaches stationary phase, when proteinases are secreted constitutively. These enzymes may directly or indirectly incite a host response, resulting in the inflammatory manifestations of dermatophytosis.

Purification and partial characterization of an exocellular proteinase from Trichophyton rubrum

An exocellular proteinase produced by Trichophyton rubrum in a glucose-peptone broth was purified from lyophilized and dialysed culture filtrate of the dermatophyte by Sephadex G-100 gel filtration and preparative polyacrylamide gel electrophoresis. The purified enzyme was a homogeneous protein of molecular weight 34700 and it could hydrolyse azoalbumin, casein, bovine serum albumin, alpha-N-benzoyl-L-arginine ethyl ester and p-toluenesulfonyl-L-arginine methyl ester but not N-benzoyl-L-tyrosine ethyl ester, alpha-N-benzoyl-DL-arginine-p-nitroanilide and keratin. The enzyme showed an alkaline pH optimum and was not activated by divalent metal ions but inhibited strongly by phenylmethylsulfonylfluoride. Thus the enzyme was identified as an alkaline serine proteinase.

Cutaneous basophil hypersensitivity and contact sensitivity after cutaneous Trichophyton mentagrophytes infection

The histopathology of cutaneous lesions and trichophytin skin test responses was examined by light microscopy after the infection of strain 2 guinea pigs with Trichophyton mentagrophytes. Skin biopsies were fixed and stained with procedures which allowed differentiation of the polymorphonuclear granulocytic leukocytes that were present in lesions or skin test reactions. Basophils comprised about one-third of the leukocytes infiltrating the 24 to 48-h trichophytin skin test reactions of guinea pigs sensitized by a cutaneous T. mentagrophytes infection. These results were comparable to the percentage of basophils counted in skin test lesions elicited by the contact agent dinitrochlorobenzene and are consistent with previously published descriptions of cutaneous basophil hypersensitivity. In contrast, the active T. mentagrophytes lesion in the skin of guinea pigs sacrificed at defined intervals after infection or reinfection did not appear to contain similarly elevated numbers of basophils. The early inflammation in primary T. mentagrophytes-induced skin lesions can be characterized histologically as a primary irritant dermatitis which evolves, during the course of the disease, into a chronic mononuclear inflammation. This shift apparently results from host sensitization to fungal antigens during infection and the concurrent development of acquired immunity. Reinfection of guinea pigs with T. mentagrophytes resulted in an accelerated cutaneous inflammation that was temporally and histologically similar to allergic contact dermatitis. These results support the hypothesis that contact sensitivity to T. mentagrophytes develops during the primary cutaneous infection of guinea pigs and is an early component of the hypersensitivity response to reinfection.

Control of exocellular proteases in dermatophytes and especially Trichophyton rubrum

The production of proteases was investigated during growth of dermatophytic fungi with special emphasis on Trichophyton rubrum. Exogenous glucose suppressed elastase production in all dermatophytes examined. The production of protease active guinea pig hair in keratin-salts broth by Microsporum gypseum. Trichophyton mentagrophytes and T. rubrum was also suppressed by glucose. Various carbohydrates added to keratin-salts broth curtailed protease production by T. rubrum as did individual amino acids but ammonium phosphate did not. Enzyme activities against guinea pig hair were compared in twenty-one diverse clinical isolates of T. rubrum cultured in keratin-salts broth. Activity also occurred towards casein, bovine serum albumin, keratin, collagen and elastin after keratin-growth. Studies concerning the properties of enzyme activities in culture filtrates of T. rubrum after keratin-growth suggested that multiple proteases occurred here. Hydrolysis of guinea pig hair and elastin were optimal at pH7 while keratinase was most active at alkaline pH. Divalent cations stimulated protease(s). Ferric ion and mercuric ion stimulated keratinase but were inhibitory to guinea pig hair hydrolysis and elastase. Chelating agents inhibited elastase and the hydrolysis of guinea pig hair more severely than keratinase and all of those effects were reversed by excess calcium. A serine-protease inhibitor, phenylmethylsulfonylfluoride (PMSF), curtailed keratinase but was less inhibitory to elastase and guinea pig hair hydrolysis. Soybean trypsin inhibitor arrested each protease.

Ecological effects of antibiotic production by dermatophyte fungi

Antibiotic production by dermatophyte fungi has been demonstrated in vivo in the lesions of patients with dermatomycoses. Patients infected with antibiotic-producing strains more frequently carried cocci resistant to penicillin and other antibiotics than did patients infected with non-producer strains. The total bacterial load was less in lesions caused by producer fungi. In vitro studies demonstrated the selection of penicillin-resistant S. aureus from mixed populations of resistant and sensitive cells.