N -Chlorotaurine Exhibits Fungicidal Activity against Therapy-Refractory Scedosporium Species and Lomentospora prolificans

Abstract

N-Chlorotaurine (NCT), a well-tolerated endogenous long-lived oxidant that can be applied topically as an antiseptic, was tested on its fungicidal activity against Scedosporium and Lomentospora, opportunistic fungi that cause severe infections with limited treatment options, mainly in immunocompromised patients. In quantitative killing assays, both hyphae and conidia of Scedosporium apiospermum, Scedosporium boydii, and Lomentospora prolificans (formerly Scedosporium prolificans) were killed by 55 mM (1.0%) NCT at pH 7.1 and 37°C, with a 1-to 4-log 10 reduction in CFU after 4 h and a 4-to >6-log 10 reduction after 24 h. The addition of ammonium chloride to NCT markedly increased this activity. LIVE/DEAD staining of conidia treated with 1.0% NCT for 0.5 to 3 h increased the permeability of the cell wall and membrane. Preincubation of the test fungi in 1.0% NCT for 10 to 60 min delayed the time to germination of conidia by 2 h to >12 h and reduced their germination rate by 10.0 to 100.0%. Larvae of Galleria mellonella infected with 1.0 ؋ 10 7 conidia of S. apiospermum and S. boydii died at a rate of 90.0 to 100% after 8 to 12 days. The mortality rate was reduced to 20 to 50.0% if conidia were preincubated in 1.0% NCT for 0.5 h or if heat-inactivated conidia were used. Our study demonstrates the fungicidal activity of NCT against different Scedosporium and Lomentospora species. A postantifungal effect connected with a loss of virulence occurs after sublethal incubation times. The augmenting effect of ammonium chloride can be explained by the formation of monochloramine.

Bactericidal and Fungicidal Activity of N -Chlorotaurine Is Enhanced in Cystic Fibrosis Sputum Medium

“…Similar to findings with other organic materials (26,42,44), the activity in ASM was even stronger than that in buffer solutions without chlorine-consuming molecules (39,40,42,43). This effect was particularly remarkable with fungi, leading to approximately 50-fold more rapid killing.…”

“…Comparisons were made with our previous data from killing assays performed in phosphate buffer (39)(40)(41)(42)(43). Remarkably, the microbicidal activities of 1% NCT in ASM were higher throughout than those in phosphate buffer at the test pH values of 6.9 to 7.1.…”

“…Furthermore, the repeated applications in vivo, by irrigation or by inhalation, could not be matched in vitro. Hyphae were not investigated here; however, their susceptibility is similar to that of conidia, as we saw in previous studies (39,42). Finally, the in vivo efficacy of NCT can be shown only in clinical trials.…”

“…All experiments were performed at 37°C in a water bath (39,40). To 3.6 ml of prewarmed ASM, 40 l of the respective suspension containing bacteria or fungal spores was added, followed by the addition of 0.4 ml NCT at time zero and vortex-mixing.…”

“…Subsequently, they were washed twice in 0.9% saline before use. Strains used were S. aureus ATCC 25923, P. aeruginosa ATCC 27853, E. coli ATCC 11229, S. aureus Smith diffuse (50) (39,42,43). ND, no data available.…”