Novel antiparasitic activity was observed for the antifungal occidiofungin. It efficaciously and irreversibly inhibited the zoonotic enteric parasite Cryptosporidium parvum in vitro with limited cytotoxicity (50% effective concentration [EC50] = 120 nM versus 50% cytotoxic concentration [TC50] = 988 nM), and its application disrupted the parasite morphology. This study expands the spectrum of activity of a glycolipopeptide named occidiofungin. Occidiofungin has poor gastrointestinal tract absorption properties, supporting future investigations into its potential activities on other enteric parasites.

Background Cryptosporidium is a genus of apicomplexan parasites, the causative agents of cryptosporidiosis in humans and/or animals. Although most apicomplexans parasitize within the host cell cytosols, Cryptosporidium resides on top of host cells, but it is embraced by a double-layer parasitophorous vacuole membrane derived from host cell. There is an electron-dense band to separate the parasite from host cell cytoplasm, making it as an intracellular but extracytoplasmic parasite. However, little is known on the molecular machinery at the host cell-parasite interface. Methods Cryptosporidium parvum at various developmental stages were obtained by infecting HCT-8 cells cultured in vitro. Immunofluorescence assay was used to detect CpEF1α with a polyclonal antibody and host cell F-actin with rhodamine-phalloidin. Recombinant CpEF1α protein was used to evaluate its effect on the invasion by the parasite. Results We discovered that a C parvum translation elongation factor 1α (CpEF1α) was discharged from the invading sporozoites into host cells, forming a crescent-shaped patch that fully resembles the electron-dense band. At the same time, host cell F-actin aggregated to form a globular-shaped plug beneath the CpEF1α patch. The CpEF1α patch remained for most of the time but became weakened and dissolved upon the completion of the invasion process. In addition, recombinant CpEF1α protein could effectively interfere the invasion of sporozoites into host cells. Conclusions CpEF1α plays a role in the parasite invasion by participating in the formation of electron-dense band at the base of the parasite infection site.

Cryptosporidium parvum is a globally important zoonotic parasite capable of causing severe to deadly diarrhea in humans and animals. Its small genome (~9.1 Mb) encodes not only a highly streamlined metabolism, but also a 25-kb, 3-module fatty acid synthase (CpFAS1) and a 40-kb, 7-module polyketide synthase (CpPKS1). The two megasynthases contain a C-terminal reductase domain to release the final products with predicted chain lengths of ≥C22 for CpFAS1 or C28 to C38 for CpPKS1.The parasite genome also encodes a discrete thioesterase ortholog, suggesting its role to be an alternative tool in releasing the final products from CpFAS1 and/or CpPKS1, or as an editor to remove non-reactive residues or aberrant intermediates, or to control starter units as seen in other parasites. In this study, we have confirmed that this C. parvum thioesterase is a type II thioesterase (thus named as CpTEII). CpTEII contains motifs and a catalytic triad characteristic to the type II thioesterase family. CpTEII is expressed during the entire parasite life cycle stages with the highest levels of expression in the later developmental stages. CpTEII showed the highest hydrolytic activity toward C10:0 decanoyl-CoA, so we speculated that CpTEII may mainly act as an editor to remove non-reactive residues and/or aberrant medium acyl chain from CpFAS1 and/or CpPKS1. However, we cannot rule out the possibility that CpTEII may also participate in the release of final products from CpFAS1 because of its moderate activity on C20:0, C:22:0 and C24:0 acyl-CoA thioesters (i.e., ~20–30% activity vs. decanoyl-CoA).

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Inter-kingdom endosymbiotic interactions between bacteria and eukaryotic cells are critical to human health and disease. However, the molecular mechanisms that drive the emergence of endosymbiosis remain obscure. Here, we describe...