The Fungal Cell Wall

Part of the antagonistic interaction between fungi, such as that between Trichoderma and other organisms, includes the production of a chitinase. This allows the Trichoderma to attack the cell wall of its target organism. The hyphae of the Trichoderma can then penetrate the target fungus and sequester its nutrients. 

---

Intrinsic (natural, innate) resistance. In one form of intrinsic resistance, the fungal cell wall (see Chapter 2) is considered to present a barrier to exclude or, more likely, to reduce the penetration by biocide molecules. The evidence to date is sketchy but the available information tentatively links cell wall glucan, wall thickness and consequent relative porosity to the sensitivity of Saccharomyces cerevisiae to chlorhexidine. 

IV. PARASITISM. Lysis by hydrolytic enzymes excreted by microorganisms is a well-known feature of mycoparasitism. Chitinase and P-l,3 glucanase (laminarase) are particularly important enzymes secreted by fungal mycoparasites capable of degrading the fungal cell wall components, chitin, and P-1,3 glucan (131-134). 

Figure 1. Hypothetical scheme of events leading to race-cultivar specific resistance or susceptibility in the rust system. If the substrate specificity of the fungal cell wall degrading enzymes (e.g., pectinases) is suitable for degradation of a specific host cell wall component (e.g., partly esterified pectin), endogenous suppressors will be produced which prevent the elicitor induced lignification response, thus leading to susceptibility.

Caspofungin is the first of a new class termed the echinocandins. It was approved in the US and in Europe in 2001. It shows activity against infections with Aspergillus and Candida, and works by inhibiting p(, 3)-D-Glucan of the fungal cell wall. Compared to amphotericin B, caspofungin seems to have a relatively low incidence of side-effects. 

Mechanism of Action An imidazole derivative that changes the permeability of the fungal cell wall. TherapeuticEffect Inhibits fungal biosynthesis of triglycerides, phospholipids. Fungistatic. 

Echinocandins act at the level of the fungal cell wall by inhibiting the synthesis of B(l-3)-glucan (Figure 48-1). This results in disruption of the fungal cell wall and cell death. 

Dimethomorph inhibits the formation of the fungal cell wall and is not cross-resistant to any known class of fungicides. 

Boucias, D. G., and Pendland, J. C. (1991). The fungal cell wall and its involvement in the pathogenic process in insect hosts. In J. P. Latge, and D. G. Boucias (Eds.), Fungal Cell Wall and Immune Response, (vol. H 53, pp. 303-316). Berlin Springer-Verlag. 

The mechanisms of metal uptake may be modified in those plants where the roots are associated with mycorrhizal fungi. Streit and Stumm (1993) suggest that metal ions might form complexes with the chitin of the fungal cell wall. However is it not clear whether this would facilitate the uptake of metals by the plant host. Some selection seems to be involved since not all the elements taken up by the fungus are released... 

Caspofungin is a cyclic polypeptide that inhibits synthesis of the fungal cell wall. It can be used in systemic mycoses due to as-pergillus fungi when amphotericin B or itroconazole cannot be employed. It is given by infusion and causes various adverse effects. 

Imidazoles (ketoconazole, miconazole, fenticonazole, clotrimazole, isoconazole, tioconazole) interfere with fungal oxidative enzymes to cause lethal accumulation of hydrogen peroxide they also reduce the formation of ergosterol, an important constituent of the fungal cell wall which thus becomes permeable to intracellular constituents. Lack of selectivity in these actions results in important adverse effects. 

The principal action of the azole group is to destabilize the fungal cell wall by inhibiting ergosterol synthesis in the cell membrane. In addition, they variably bind to and inhibit mitochondrial... 

Flucytosine is a fluorinated pyrimidine that is transported across the fungal cell wall by a permease, where it is deaminated to the cytotoxic principal fluorouracil. Some fungi may lack the permease and are resistant to the drug and its clinical use is usually restricted to treating Candida spp. infection, although even here resistance may arise. It is synergistic with amphotericin B and... 

---