Acanthamoeba keratitis (AK) is a severe infection of the cornea. Prevention and treatment are difficult due to the inefficacy of currently available compounds. The impact of many commonly used compounds for routine examinations of Acanthamoeba is unexplored but might offer insight useful in combatting AK. In this study, we demonstrate that sodium metabisulfite, a common preservation constituent of eye care solutions, was found to be active against Acanthamoeba trophozoites at concentrations lower than that commonly found in eye drops (IC₅₀ 0.03 mg/mL). We demonstrate that sodium metabisulfite depletes thiamine from growth medium and that Acanthamoeba is a thiamine auxotroph, requiring thiamine salvage for growth. The inhibitory effects of sodium metabisulfite can be overcome by thiamine supplementation. These results are consistent with the lack of key enzymes for thiamine biosynthesis in the genome of Acanthamoeba, an area which might prove exploitable using new or existing compounds. Indeed, this study highlights sodium metabisulfite as a useful inhibitor of Acanthamoeba castellanii trophozoites in vitro and that it acts, at least in part, by limiting available thiamine.

Gregarines are a notably understudied but widespread group of protists that colonise aquatic and terrestrial invertebrates. This limited understanding of gregarines and their interactions with their hosts results partly from the absence of established culturing techniques and our understanding therefore has heavily relied on field collections. This study utilised for the first time cultured Gammarus pulex populations and comparative functional response models to explore the effects of gregarine colonisation on the host's consumption of Chironomid prey. This study shows that both positive and negative G. pulex displayed a Type II functional response. There were no statistical differences in the functional response parameters between the two groups. These results suggest that, under the study conditions, gregarines may function as commensal symbionts within their G. pulex host. This is consistent with growing evidence for gregarines acting across a range of symbiotic roles within their hosts. These findings provide insight into the role of gregarines in G. pulex, an invertebrate species frequently used for field- and lab-based experiments, contributing to the evidence of the complex and varied gregarine host-symbiont interactions.