The Evaluation of Surface Charges of Ascaris Lumbricoides, Giardia Duodenalis, and Taenia spp., in Preserved Fecal Samples Processed in Natura.

OBJECTIVE: Parasite structures eliminated in feces have chemical characteristics resulting from their interactions with the environment in which they are found. These poorly documented physicochemical conditions may interfere with separation techniques used to detect helminth eggs and larvae, as well as protozoan cysts, oocysts, and spores. This interference negatively affects diagnostic protocols for these pathogens, which are generally low to moderate in sensitivity. As such, we sought to evaluate the surface charge by zeta potential (ZP) of the species Ascaris lumbricoides, Giardia duodenalis, and Taenia spp. METHODS: We screened fecal samples that tested positive for these parasites at high intensity. These positive samples were then filtered through tubes containing 400 µm and 200 µm meshes, after which a 500 µL aliquot was diluted with 9 mL of deionized water and centrifuged (490 g / 5 min). This dilution and centrifugation procedure was performed 5 times to obtain a concentrated parasite sediment, which was then transferred to Petri dishes containing 7.5% formalin in deionized water. Eggs and cysts were visualized with stereomicroscopy equipment, captured with a 10 µL micropipette, and stored in Eppendorf tubes (2 mL). RESULTS: Zeta potential values were analyzed with a Zetasizer nano device, and the average data obtained from in triplicate were - 28 mV, - 21.9 mV, and - 18.4 mV for G. duodenalis, A. lumbricoides, and Taenia spp., respectively. CONCLUSION: We conclude that the negative charges presented on the surfaces of these parasite structures in natural fecal samples can negatively affect laboratory diagnostic techniques.