Cargando…

Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans

Cryptococcal meningoencephalitis remains a global health threat with limited treatment options. Currently, the most effective treatment regimens are based on a combination therapy of flucytosine with either amphotericin B or fluconazole. Slow but steady progress is being made toward universal access...

Descripción completa

Detalles Bibliográficos
Autores principales: Jezewski, Andrew J., Ristow, Laura C., Krysan, Damian J.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Society for Microbiology 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10101005/
https://www.ncbi.nlm.nih.gov/pubmed/36719209
http://dx.doi.org/10.1128/spectrum.04783-22
_version_ 1785025413943132160
author Jezewski, Andrew J.
Ristow, Laura C.
Krysan, Damian J.
author_facet Jezewski, Andrew J.
Ristow, Laura C.
Krysan, Damian J.
author_sort Jezewski, Andrew J.
collection PubMed
description Cryptococcal meningoencephalitis remains a global health threat with limited treatment options. Currently, the most effective treatment regimens are based on a combination therapy of flucytosine with either amphotericin B or fluconazole. Slow but steady progress is being made toward universal access to flucytosine-based therapies. The broadening access to flucytosine combination therapies will be accompanied by the need for microbiological methods that reliably determine strain susceptibility. This is especially true considering that flucytosine susceptibility can vary widely across clinical isolates. Identifying culture conditions that best represent the host environment are likely optimal and may even be required for accurately determining in vivo flucytosine susceptibility. Here, we report that culture conditions incorporating host-like concentrations of carbon dioxide (CO(2)) potentiated flucytosine susceptibilities across clinical isolates (10 of 11) that exhibited a range of MIC values under ambient growth conditions (2 to 8 μg/mL) by standard Clinical and Laboratory Standards Institute susceptibility testing. CO(2) induced a dose-dependent increase in flucytosine susceptibility between 2- and 8-fold over standard conditions. The CO(2)-dependent increase in flucytosine susceptibility did not correspond to an increase in fluorouracil susceptibility, indicating a central role for flucytosine uptake through the cytosine permease in the presence of host-like CO(2) concentrations. Indeed, the expression of the cytosine permease gene (FCY2) was induced 18- to 60-fold in the mouse lung environment. Therefore, the activity of flucytosine is likely to be very dependent upon host environment and may not be well represented by standard in vitro susceptibility testing. IMPORTANCE Cryptococcus neoformans causes life-threatening infections of the brain. The most effective treatment regimens are based on flucytosine-based combination therapy, which has led to increasingly successful broadening of access to flucytosine globally. Wider use of flucytosine-based therapies for cryptococcal infections will require the ability to reliably determine clinical isolate susceptibilities. We showed that host-like carbon dioxide stress affected flucytosine susceptibility, and this likely occurred through flucytosine uptake. We further showed that the gene encoding the permease, FCY2, and that is responsible for flucytosine uptake was strongly induced during cryptococcal infection. Our data provide insights into the distinctions between the activity of flucytosine in the host environment and during in vitro susceptibility testing.
format Online
Article
Text
id pubmed-10101005
institution National Center for Biotechnology Information
language English
publishDate 2023
publisher American Society for Microbiology
record_format MEDLINE/PubMed
spelling pubmed-101010052023-04-14 Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans Jezewski, Andrew J. Ristow, Laura C. Krysan, Damian J. Microbiol Spectr Observation Cryptococcal meningoencephalitis remains a global health threat with limited treatment options. Currently, the most effective treatment regimens are based on a combination therapy of flucytosine with either amphotericin B or fluconazole. Slow but steady progress is being made toward universal access to flucytosine-based therapies. The broadening access to flucytosine combination therapies will be accompanied by the need for microbiological methods that reliably determine strain susceptibility. This is especially true considering that flucytosine susceptibility can vary widely across clinical isolates. Identifying culture conditions that best represent the host environment are likely optimal and may even be required for accurately determining in vivo flucytosine susceptibility. Here, we report that culture conditions incorporating host-like concentrations of carbon dioxide (CO(2)) potentiated flucytosine susceptibilities across clinical isolates (10 of 11) that exhibited a range of MIC values under ambient growth conditions (2 to 8 μg/mL) by standard Clinical and Laboratory Standards Institute susceptibility testing. CO(2) induced a dose-dependent increase in flucytosine susceptibility between 2- and 8-fold over standard conditions. The CO(2)-dependent increase in flucytosine susceptibility did not correspond to an increase in fluorouracil susceptibility, indicating a central role for flucytosine uptake through the cytosine permease in the presence of host-like CO(2) concentrations. Indeed, the expression of the cytosine permease gene (FCY2) was induced 18- to 60-fold in the mouse lung environment. Therefore, the activity of flucytosine is likely to be very dependent upon host environment and may not be well represented by standard in vitro susceptibility testing. IMPORTANCE Cryptococcus neoformans causes life-threatening infections of the brain. The most effective treatment regimens are based on flucytosine-based combination therapy, which has led to increasingly successful broadening of access to flucytosine globally. Wider use of flucytosine-based therapies for cryptococcal infections will require the ability to reliably determine clinical isolate susceptibilities. We showed that host-like carbon dioxide stress affected flucytosine susceptibility, and this likely occurred through flucytosine uptake. We further showed that the gene encoding the permease, FCY2, and that is responsible for flucytosine uptake was strongly induced during cryptococcal infection. Our data provide insights into the distinctions between the activity of flucytosine in the host environment and during in vitro susceptibility testing. American Society for Microbiology 2023-01-31 /pmc/articles/PMC10101005/ /pubmed/36719209 http://dx.doi.org/10.1128/spectrum.04783-22 Text en Copyright © 2023 Jezewski et al. https://creativecommons.org/licenses/by/4.0/This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0/) .
spellingShingle Observation
Jezewski, Andrew J.
Ristow, Laura C.
Krysan, Damian J.
Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans
title Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans
title_full Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans
title_fullStr Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans
title_full_unstemmed Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans
title_short Carbon Dioxide Potentiates Flucytosine Susceptibility in Cryptococcus neoformans
title_sort carbon dioxide potentiates flucytosine susceptibility in cryptococcus neoformans
topic Observation
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10101005/
https://www.ncbi.nlm.nih.gov/pubmed/36719209
http://dx.doi.org/10.1128/spectrum.04783-22
work_keys_str_mv AT jezewskiandrewj carbondioxidepotentiatesflucytosinesusceptibilityincryptococcusneoformans
AT ristowlaurac carbondioxidepotentiatesflucytosinesusceptibilityincryptococcusneoformans
AT krysandamianj carbondioxidepotentiatesflucytosinesusceptibilityincryptococcusneoformans