Precision-cut lung slices as an ex vivo model to study Pneumocystis murina survival and antimicrobial susceptibility

Pneumocystis pneumonia (PCP) is a serious fungal lung infection caused by Pneumocystis jirovecii in immunosuppressed individuals. The lack of viable in vitro/ex vivo PCP models has greatly hindered the progress in studying the biology of these fungi, the host/pathogen interactions, as well as antifungal susceptibility testing. In this study, we show the utility of precision-cut lung slices (PCLS) to support the survival of Pneumocystis murina in vitro. We cultured PCLS tissue derived from wild type and immunocompromised mice with a P. murina inoculum in submerged or air-liquid interface models for up to 14 days. We isolated total RNA from the cultured lung tissues at days 0, 3, 7, 10, and 14 and analyzed for the expression of host lung genes and P. murina genes (Gsc1 for asci and Sp for trophs) by real-time quantitative PCR. When cultured in media alone, P. murina died gradually within a few days. However, when cultured on PCLS, both the troph and ascus forms survived throughout the incubation period of 2 weeks. Moreover, immunohistochemistry staining of P. murina inoculated PCLS sections using polyclonal anti-Pneumocystis sera and showed evidence of fungal aggregation and possible biofilm formation. Additionally, in vitro (PCLS) antibiotic susceptibility testing using commonly used antifungal drugs confirmed successful targeting of the troph and ascus forms by trimethoprim sulfamethoxazole and the ascus form by echinocandins.IMPORTANCEOur study reveals the potential of precision-cut lung slices as an ex vivo platform to study the growth/survival of Pneumocystis spp. that can facilitate the development of new anti-fungal drugs.