In Vitro Anticryptosporidial Activity of Ranalexin Alone and in Combination with Other Peptides and with Hydrophobic Antibiotics

 The in vitro activity of ranalexin alone and in combination with other cationic peptides, macrolides, rifampin, and rifabutin was investigated against a clinical isolate of Cryptosporidium parvum. Susceptibility tests were performed by inoculation of the isolate onto cell monolayers and determining the parasite count after 48 h of incubation at 37  °C. Antibiotic-free cultures were used as controls in the study. Ranalexin showed low anticryptosporidial activity: it suppressed the growth of parasites by ≥40% at 50 μM. Ranalexin showed enhanced activity when it was combined with noninhibitory concentrations of other compounds: a 74.4–94.1% reduction in the number of parasites was observed when ranalexin 50 μM was combined with magainin II 50 μM, indolicidin 50 μM, clarithromycin 8 mg/l, azithromycin 8 mg/l, rifampin 8 mg/l, and rifabutin 8 mg/l. The results suggest that ranalexin may be effective in inhibiting Cryptosporidium parvum growth in vitro upon combination with other peptides and hydrophobic antibiotics.