Killing of Coccidioides immitis by hypochlorous acid or monochloramine

To identify possible explanations for the resistance of Coccidioides immitis to killing by human neutrophils, its susceptibility to typical oxidants generated during the neutrophil respiratory burst was compared to the sensitivity of other microbes. When microbial suspensions were exposed to hypochlorous acid, arthroconidia or spherules of C. immitis were killed more slowly than yeast cells of Candida (Torulopsis) glabrata or Staphylococcus aureus. In contrast, exposure to the more lipophilic oxidant, monochloramine, produced equivalent rates of killing for spherules and yeast cells of C. glabrata, and arthroconidia were killed more rapidly. When larger microbial concentrations were used, significantly greater concentrations of hypochlorous acid were required to kill equivalent percentages of spherules as compared to yeast cells of C. glabrata. Mixing studies with either whole spherules or extracts of spherules demonstrated that these substances could also block hypochlorous acid killing of S. aureus. These studies suggest possible mechanisms whereby C. immitis might resist oxidative phagocytic killing.