In Vitro Efficacy of Nikkomycin Z against the Human Isolate of the Microsporidian Species Encephalitozoon hellem

Since 1985 microsporidia have been recognized as a cause of emerging infections in humans, mainly in immunocompromised human immunodeficiency virus-positive subjects. As chitin is a basic component of the microsporidian infective stage, the spore, we evaluated in vitro the susceptibility of a human-derived strain of Encephalitozoon hellem to nikkomycin Z, a peptide-nucleoside antibiotic known as a competitive inhibitor of chitin synthase enzymes. Transmission electron microscopy showed that this drug, at 25 μg/ml, reduced the number of parasitic foci by about 35% ± standard deviation after 7 days of culture (P < 0.0001) and induced cell damage of both mature and immature spores and also other sporogonic and merogonic stages. In particular, an irregular outline of the cell shape and an abnormally condensed cytoplasm in meronts and sporonts were documented. Also, the polar tubule and the polaroplast membranes appeared disarrayed in the sporoblast stage. The spore wall showed an enlarged endospore and delaminated exospore. Mature spores had a complete cytoplasmic disorganization and a swollen and delaminated cell wall. No ultrastructural cell damage was observed in uninfected control cultures treated with the drug.

自1985年起，微孢子虫（microsporidia）已被确认为人类新发感染的致病菌，此类感染主要累及免疫功能低下的人类免疫缺陷病毒（human immunodeficiency virus, HIV）阳性受试者。由于几丁质（chitin）是微孢子虫感染阶段——孢子的核心组成成分，本研究体外评估了人源赫氏脑炎微孢子虫（Encephalitozoon hellem）菌株对尼可霉素Z（nikkomycin Z）的药敏性；尼可霉素Z是一种可竞争性抑制几丁质合酶（chitin synthase）活性的肽核苷类抗生素。透射电子显微镜（transmission electron microscopy）检测显示，浓度为25 μg/ml的该药物可使培养7天后的寄生虫病灶数量减少约35%±标准差（P < 0.0001），并对成熟、未成熟孢子以及其他孢子生殖、裂殖生殖阶段的虫体造成细胞损伤。具体而言，裂殖体（meronts）与产孢体（sporonts）可见细胞外形不规则、细胞质异常浓缩；成孢子细胞（sporoblast）阶段的极丝（polar tubule）与极体膜（polaroplast membranes）结构紊乱。孢子壁表现为内壁增厚、外壁分层脱落；成熟孢子则出现完全的细胞质紊乱，以及细胞壁肿胀且分层脱落的改变。经该药物处理的未感染对照培养物中，未观察到任何超微结构层面的细胞损伤。