Effects of lysozyme and chitinase on the spherules of Coccidioides immitis in vitro

Compounds active against cell walls of medically important fungi

A number of substances that directly or indirectly affect the cell walls of fungi have been identified. Those that actively interfere with the synthesis or degradation of polysaccharide components share the property of being produced by soil microbes as secondary metabolites. Compounds specifically interfering with chitin or beta-glucan synthesis have proven effective in studies of preclinical models of mycoses, though they appear to have a restricted spectrum of coverage. Semisynthetic derivatives of some of the natural products have offered improvements in activity, toxicology, or pharmacokinetic behavior. Compounds which act on the cell wall indirectly or by a secondary mechanism of action, such as the azoles, act against diverse fungi but are usually fungistatic in nature. Overall, these compounds are attractive candidates for further development.

Models of cell differentiation in conidial fungi

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Morphogenesis throughout saprobic and parasitic cycles of Coccidioides immitis

The fungus, Coccidioides immitis, differs from other dimorphic pathogens in that its parasitic stage is a complex morphogenic cycle, raising the question that changes and composition during morphogenesis might influence host responses. As a prelude to examining the interaction of fungal morphogenesis and host responses, the life cycle of this fungus has been examined in greater detail than previously accomplished. During saprobic development, alternating enterothallic arthroconidia are formed as infectious propagules. The outer wall is broken and loosely adherent. Under in vitro conditions supporting the parasitic cycle, multinucleate arthroconidia transform into uninucleate round cells. Rapid, synchronous, nuclear replication is initiated, accompanied by increase in cell mass and deposition of new cell wall substance. As karyokinesis ceases, morphologic differentiation begins with invagination of the inner layers of the spherule wall and then is progressive, eventually segmenting the protoplasm into uninucleate endospores grouped in clusters within a hyaline membrane. Endospores, escaping through a break in the spherule wall, are held in aggregates by fibrils which are stretched and broken as endospores separate. It would seem that rapid production of hundreds of progeny from an original single cell, protected during development by an enclosing spherule wall and then released in clusters, should favor establishment of the fungus in a host, and dynamic changes in the cell wall during morphogenesis should influence the host response.

Role of lymphocytes in macrophage-induced killing of Coccidioides immitis in vitro

Peritoneal macrophages from normal mice phagocytized arthroconidia and endospores of Coccidioides immitis without affecting the viability of the spores within 4 h after infection. In contrast, macrophages, when infected in the presence of lymphocytes from immune mice, significantly reduced the viability of phagocytized endospores and arthroconidia. The inability of macrophages from normal mice to kill C. immitis may in part be explained by the observation that C. immitis appeared to inhibit fusion of the phagosomes containing fungal spores with the lysosomes within the macrophages. However, fusion of phagosomes containing spores and lysosomes was observed in macrophages infected in the presence of lymphocytes from immune mice.

Immunization of mice against coccidioidomycosis with a subcellular vaccine

In vitro-cultivated spherules of Coccidioides immitis were disrupted in a Braun homogenizer. The resultant wall fragments were separated from cell sap and endospores by centrifugation. Extraction of the walls with phosphate-buffered saline yielded a subcellular fraction that was immunogenic in mice. This fraction, which contained polysaccharide and protein, gave substantial protection against intranasal challenge with a usually lethal dose (1,000) of arthrospores, provided that it was administered with adjuvant.

Inhibition of Coccidioides immitis in vitro and enhancement of antiococcidiodial effects of amphotericin B by polymyxin B

Growth of the spherule phase of Coccidioides immitis in liquid glucose-mineral salts medium was suppressed for 13 days by 5 to 10 mug of polymyxin B per ml. Inhibition of growth was also noted when filter paper disks containing polymyxin B were placed on the surface of arthrospore-seeded defined medium solidified with refined agar. The antibiotic evidently damaged the cytoplasmic membrane inasmuch as spherules suspended in distilled water containing 10 mug of polymyxin B per ml rapidly lost nucleotides. Leakage of nucleotides was prevented by 0.1 M Ca(2+). The anticoccidioidal activity of amphotericin B (0.02 to 0.08 mug/ml) was enhanced by 2.5 mug of polymyxin B per ml. Colistin (polymyxin E) methanesulfonate did not inhibit spherule growth at concentrations as high as 50 mug/ml. This may be because colistin, though structurally similar to polymyxin B, is not cationic because its gamma-amino groups are masked by methanesulfonate radicals.

Inhibition by lysozyme of growth of the spherule phase of Coccidioides immitis in vitro

Development of mature endosporulating spherules from an endospore inoculum was markedly inhibited by human or hen egg-white (HEW) lysozyme at 5 mug/ml. Mature spherules formed in medium containing 5 mug per lysozyme per ml (3.3 x 10(-7) M) were approximately 50% smaller than control spherules. In addition, lysozyme induced a large portion of the endospore inoculum to revert to the mycelial growth phase. Increasing lysozyme concentrations to 10 or 20 mug/ml prompted a nearly complete reversion of the inoculum to the mycelial phase. Mature endosporulating spherules removed from growth medium and resuspended in a solution of human or HEW lysozyme at 18 mug/ml in distilled water prompted leakage of four to five times as much of materials absorbing maximally at 260 nm into the supernatant as untreated control spherules during 90 min of incubation. This four- to fivefold increase in nucleotide loss was evident at 4, 25, and 37 C. The permeability of 1-day-old immature spherules and 8-day-old endospores was considerably altered by lysozyme treatment of cells suspended in distilled water. Large amounts of potassium and nucleotides were rapidly lost by each type of cell when treated with 20 mug of lysozyme per ml. After 270 min of exposure to lysozyme, 98% of the immature spherules and 25% of the endospores were nonviable. Lysozyme adsorption by formalin-killed spherules in the presence of varying concentrations of calcium ion and the rapid alteration of permeability seen after lysozyme treatment suggested that the cell membrane was damaged as a result of binding lysozyme.