Quantifying metabolic activity of Ascaris suum L3 using resazurin reduction

Abstract

Background Helminth infections are an important public health problem in humans and have an even greater impact on domestic animal and livestock welfare. Current readouts for anthelmintic drug screening assays are stage development, migration, or motility that can be subjective, laborious, and low in throughput. The aim of this study was to apply and optimize a fluorometric technique using resazurin for evaluating changes in the metabolic activity of Ascaris suum third-stage larvae (L3), a parasite of high economic relevance in swine. Methods Ascaris suum L3 were mechanically hatched from 6- to 8-week embryonated and sucrose-gradient-enriched eggs. Resazurin dye and A. suum L3 were titrated in 96-well microtiter plates, and resazurin reduction activity was assessed by fluorometry after 24 h of incubation. Fluorescence microscopy was used to localize the resazurin reduction site within the larvae. Finally, we exposed A. suum L3 to various stress conditions including heat, methanol, and anthelmintics, and investigated their impact on larval metabolism through resazurin reduction activity. Results We show that the non-fluorescent dye resazurin is reduced inside vital A. suum L3 to fluorescent resorufin and released into the culture media. Optimal assay parameters are 100–1000 L3 per well, a resazurin concentration of 7.5 µg/ml, and incubation at 37 °C/5% CO2 for 24 h. An intact L2 sheath around the L3 of A. suum completely prevents the uptake of resazurin, while in unsheathed L3, the most intense fluorescence signal is observed along the larval midgut. L3 exposed to methanol or heat show a gradually decreased resazurin reduction activity. In addition, 24 h exposure to ivermectin at 0.625 µM, mebendazole at 5 µM, and thiabendazole from 10 to 100 µM significantly decreased larval metabolic activity by 55%, 73%, and 70% to 89%, respectively. Conclusions Together, our results show that both metabolic stressors and anthelmintic drugs significantly and reproducibly reduce the resazurin reduction activity of A. suum L3, making the proposed assay a sensitive and easy-to-use method to evaluate metabolic activity of A. suum L3 in vitro. Graphical Abstract

Acute Ascaris infection impairs the effector functions of natural killer cells in single and Salmonella co-infected pigs

“…6 pigs ( Ascaris group) were orally infected with 2000 embryonated Ascaris suum eggs on 4 consecutive days (total inoculation dose of 8000 eggs, embryonation rate 97.80%). Ascaris suum egg collection, density purification and evaluation of the embryonation rate were carried out as previously reported 52 . The Ascaris group pigs were dissected two weeks post-infection.…”

Evaluation of copromicroscopy, multiplex-qPCR and antibody serology for monitoring of human ascariasis in endemic settings

“…Eggs were obtained by culturing female worms overnight in Hank’s balanced salt solution (HBSS-AB) supplemented with 200U/mL Penicillin, 200μg/mL Streptomycin, 50μg/mL Gentamicin, and 0.25μg/mL Amphotericin B. Eggs were washed several times in water, and placed in 0.1% formalin-containing distilled water for four weeks for embryonation. Hatched L3 were collected as previously described [ 24 ], washed twice in HBSS-AB, and homogenised with Fast Prep-24 for 30s using lysing tubes A (Innuspeed, Germany). Centrifugation was done at 4°C, 16,500x g for 20min and the supernatant was sterile-filtered with Millex-GV (0.22μm).…”

Th2-biased immune responses to body migrating Ascaris larvae in primary infection are associated with pathology but not protection

“…Under the same conditions 7 to 8 weeks old female wild-type BALB/c (BALB/c WT) and BALB/c eosinophil-deficient mice (BALB/c ΔdblGATA) were caged together upon arrival. Thereafter, 2,500 fully embryonated Ascaris suum eggs (preparation according to Kundik et al 62 ) suspended in 150 µL of drinking water were used to infect the 9-weeks old female mice via oral gavage. Naïve mice as well as mice at day 4 p.i.…”