The caspofungin paradoxical effect is a tolerant "Eagle effect" in the filamentous fungal pathogen Aspergillus fumigatus

Cell responses against antifungals different from resistance have been rarely studied in filamentous fungi, while terms such as tolerance and persistence are well-described for bacteria and increasingly examined in yeast-like organisms. <i>Aspergillus fumigatus </i>is a filamentous fungal pathogen that causes a disease named aspergillosis and caspofungin (CAS), a fungistatic drug, used as second-line therapy. Some <i>A. fumigatus </i>clinical isolates can survive and grow in CAS concentrations above the minimum effective concentration (MEC), a phenomenon known as “caspofungin paradoxical effect” (CPE). Here we evaluated the CPE in 67 <i>A. fumigatus </i>clinical isolates by calculating the Recovery Rate (RR) value, where isolates with RR ≥ 0.1 are considered CPE⁺ while isolates with RR &lt; 0.1 are classified as CPE^-. Conidia produced by three CPE⁺ clinical isolates, CEA17 (RR=0.42), Af293 (RR=0.59), CM7555 (RR=0.38) all showed the ability to grow in high levels of CAS while all conidia produced by the CPE^- isolate IFM61407 (RR=0.00) showed no evidence of paradoxical growth. Given the importance of calcium/calcineurin/transcription factor CrzA pathway in CPE regulation, we also demonstrated that all Δ<i>crzA</i>^CEA17 (CPE⁺) conidia showed CPE while 100% of Δ<i>crzA</i>^Af293(CPE^-) were CPE^-.As all spores derived from an individual strain were phenotypically indistinct with respect to CPE it is likely that CPE is a genetically encoded adaptive trait that should be considered an antifungal tolerant phenotype. As the RR parameter shows that the strength of the CPE is not uniform between strains, we propose that the mechanisms that govern this phenomenon are multi-factorial. <b> </b>

除耐药性外，丝状真菌针对抗真菌药物的细胞应答研究鲜有报道；而诸如耐受（tolerance）与持留（persistence）等概念在细菌中已有充分阐释，并在类酵母生物中得到日益深入的研究。烟曲霉（*Aspergillus fumigatus*）是一种丝状真菌病原体，可引发曲霉病；卡泊芬净（caspofungin, CAS）是一种抑菌类抗真菌药物，常作为二线治疗用药。部分烟曲霉临床分离株可在高于最低有效浓度（minimum effective concentration, MEC）的卡泊芬净环境中存活并增殖，该现象被称为‘卡泊芬净反常效应’（caspofungin paradoxical effect, CPE）。本研究通过计算恢复率（Recovery Rate, RR）值，对67株烟曲霉临床分离株的CPE进行了评估：RR≥0.1的分离株被定义为CPE阳性（CPE⁺），RR<0.1的分离株则归类为CPE阴性（CPE^-）。三株CPE阳性临床分离株CEA17（RR=0.42）、Af293（RR=0.59）与CM7555（RR=0.38）产生的分生孢子（conidia）均可在高浓度卡泊芬净环境中增殖；而CPE阴性分离株IFM61407（RR=0.00）产生的所有分生孢子均未表现出反常生长现象。鉴于钙/钙调磷酸酶/转录因子CrzA通路在CPE调控中的重要作用，本研究还证实，ΔcrzA^CEA17（CPE⁺）的所有分生孢子均表现出CPE表型，而ΔcrzA^Af293（CPE^-）的分生孢子100%为CPE阴性。由于同一菌株产生的所有孢子在CPE表型上并无差异，提示CPE很可能是一种由遗传编码的适应性性状，应将其归为抗真菌耐受表型。由于恢复率参数显示不同菌株的CPE强度并不均一，本研究提出，调控该现象的分子机制是多因素共同作用的。