Inhibition by Lysozyme of Growth of the Spherule Phase of Coccidioides immitis In Vitro

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Development of mature endosporulating spherules from an endospore inoculum was markedly inhibited by human or hen egg-white (HEW) lysozyme at 5 μg/ml. Mature spherules formed in medium containing 5 μg per lysozyme per ml (3.3 × 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 μg/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 μg/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 μg 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.

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