The cell wall of fungal human pathogens: Its possible role in host-parasite relationshipsA review

Abstract

The ability of some fungi to cause disease in animals, and particularly in humans, appears to be related to some peculiar trait of their metabolism not shared by taxonomically related species, so that among thousands of species of fungi, only some 100 are considered pathogenic for humans.Recently, there has been an increase in the basic research aimed at elucidating the physiology, biochemistry, and mechanisms of pathogenicity of the fungi in addition to the responses of the infected host. The results from these studies are often difficult to compare because of the lack of reference cultures, and because variability among laboratories are found for many parameters such as origin of isolates, growth conditions, and fractionation procedures used to obtain chemically defined components of cell walls.This review deals with cell wall structures and their influence in host-parasite relationships in those relatively few pathogenic fungi on which substantial literature exists. Serological properties of the walls are included when available. Readers interested in medical and biological aspects of fungi may consult Rippon's (140) and Emmons et al.'s (51) textbooks, among others. Some reviews on microbial surfaces and their relationships to pathogenicity have been published (160 162)2The pathogenic fungi included in this review are classified according to their cell wall structure, following Bartnicki-Garcia's criteria (15) on the distribution of the two major polysaccharides within the fungal cell wall. This classification is based on the fact that fungi may be subdivided into various categories according to the chemical nature of their walls, and that these categories closely parallel conventional taxonomic boundaries. As seen in Table l, this classification is based on dual combinations of those polysaccharides which appear to be the principal component of vegetative walls, disregarding the presence of small amounts of other classifying polysaccharides. The few pathogenic fungi whose cell walls have been studied to some extent belong to Bartnicki-Garcia's categories 5 (chitin-glucan) and 6 (mannan-glucan) ( Table 2). Besides these main polysaccharides, some minor components of the cell wall may also play important roles in pathogenicity, as antigens, or as virulence factors, and they will be mentioned in this review. DermatophytesDermatophytes are a highly specialized group of fungi that, through long evolutionary processes became adapted to invade, colonize, and nourish themselves on the keratinized tissues of animals. The three genera of dermatophytes are: Trichophyton, Microsporum, and Epidermophyton, of which 21, 15, and 1 species, respectively, are currently considered valid members (1) (ln the Vth Panamerican Conference on Mycoses, April 1980, Caracas, these figures were raised to 27, 16, and 2, respectively). Mating studies have revealed that, for some cases, what were considered as single species of Microsporum and Trichophyton, actually represent complexes of more than one species, indis- Mycopathologia7...

Comparison of transcription of multiple genes during mycelia transition to yeast cells of Paracoccidioides brasiliensis reveals insights to fungal differentiation and pathogenesis

“…Some biochemical processes related to the dimorphic transition had been elucidated. In this way, the dimorphic transition involves alterations in the cell wall composition and in the structure of carbohydrates polymers [4]. Hyper expression of the enzymes of the sulfur metabolism in the yeast phase during the fungal transition to yeast reinforces previous findings that this metabolic pathway could be important for this differentiation process [5,6].…”

“…Glycosyltransferases play vital roles in the biological function of native proteins, as well as, in the biosynthesis of numerous molecules within fungi, including cell wall components and its induced expression putatively reflect the cell wall remodeling that occurs during P. brasiliensis morphological transition [4,21]. The novel/induced genes encode glycosyltransferases that could be related to galactosylation of N-and O-glycans, as described in S. cerevisiae [42].…”

A cytochemical study of acid carbohydrates on the surface of Candida lipolytica grown in tween 80-containing medium

“…Ultrastructural characteristics of the fungal cell wall, septal pore, mitochondria, nucleus, organelles and plasma membrane of many taxonomic groups, including medically important species, have been extensively studied, and already reviewed (28,40,47,53,54,57). However, there is no detailed analysis of the C. lipolytica ultrastructure is available.…”

Experimental dermatophytosis in hamsters inoculated with Trichophyton mentagrophytes in the cheek pouch

“…These organisms are divided in 3 genders: Trichophyton (T), Microsporum, and Epidermophyton, that can induce a variety of inflammatory reactions 15 . Different from other pathogenic fungi, dermatophytes are not opportunists and frequently infect health individuals.…”