Eimeria tenella: effect of narasin, a polyether antibiotic on the ultrastructure of intracellular sporozoites

Early Transcriptional Response to Monensin in Sensitive and Resistant Strains of Eimeria tenella

Eimeria parasites are the causative agents of coccidiosis, a common parasitic disease in poultry and livestock that causes significant economic losses to the animal husbandry industry. Ionophore coccidiostats, such as monensin and salinomycin, are widely used for prophylaxis of coccidiosis in poultry. Unfortunately, widespread drug resistance has compromised their efficacy. As a result, there is an increasing need to understand the targets and resistance mechanisms to anticoccidials. However, how Eimeria parasite genes respond to ionophores remains unclear. In this study, resistance to monensin was induced in E. tenella through serial generations of selection. Both sensitive and resistant E. tenella sporozoites were treated with 5 μg/ml monensin for 0, 2, and 4 h, respectively. Gene transcription profiles were then compared by high-throughput sequencing. The results showed that protein translation-related genes were significantly downregulated after drug induction. A total of 1,848 DEGs were detected in the sensitive strain after 2 h of exposure, whereas only 31 were detected in the resistant strain. Among these DEGs in the sensitive strain, genes associated with protein degradation were significantly upregulated, supporting the autophagy-like parasite killing theory. Then, 4 h of exposure resulted in additional 626 and 621 DEGs for sensitive and resistant strains, respectively. This result implies that the gene transcription in sensitive strain is more susceptible to monensin treatment. Our results provide gene expression landscapes of E. tenella following monensin treatment. These data will contribute to a better understanding of the mechanism of drug resistance to polyether ionophores in coccidia.

Alkaline-earth metal(II) complexes of salinomycin – spectral properties and antibacterial activity

In the present paper the synthesis and structural characterization of alkaline-earth metal(II) complexes of the polyether ionophorous antibiotic salinomycinic acid (SalH.H2O) are discussed. The complexes [M(Sal)2(H2O)2] (M = Mg2+, 1; Ca2+, 2; Sr2+, 3; Ba2+, 4) were obtained reacting salinomycinic acid and Et4NOH with the corresponding metal(II) salts at metal-to-ligand-to-base molar ratio of 1:1:1. The spectral properties of 1–4 were characterized using infrared spectroscopy, fast atom bombardment-mass spectrometry, nuclear magnetic resonance and elemental analysis data. The crystallinity degree and morphology of complex 2 were studied by X-ray powder diffraction and transmission electron microscopy. The biometal(II) salinomycinate complexes 1 and 2 possess an enhanced antimicrobial activity compared to the parent antibiotic against Gram-positive bacteria. The comparison between the effectiveness of the complexes, reported here, and the already known isostructural coordination species of salinomycin and monensin (MonH.H2O), revealed that magnesium(II) and calcium(II) monensinates appear to be promising antibacterial agents against Bacillus subtilis, Bacillus cereus and Micrococcus luteus.

In Vitro Assessment of Anticoccidials: Methods and Molecules

Simple Summary

Coccidiosis is a major problem in poultry production, leading to significant economic losses. Due to the outbreak of resistance to the available treatments, research is focusing on finding new molecules that work against the pathogen. Botanical compounds represent promising alternatives, but reliable in vitro tests are needed for their screening and to understand their mechanism of action. Research in vitro involves studies on the environmental phase of the parasite and studies on the endogenous development, which occurs inside the host cells and that requires cell cultures or in ovo models to be studied. This review aims to summarize the protocols that have been successfully applied so far, as well as to suggest potential cues to improve research on this field. Moreover, as the surge of botanicals as anticoccidial molecules is on the rise, the intent is to provide an overview of the methods to assess their effectiveness in vitro in comparison with conventional drugs.

Abstract

Avian coccidiosis is a disease causing considerable economic losses in the poultry industry. It is caused by Eimeria spp., protozoan parasites characterized by an exogenous–endogenous lifecycle. In vitro research on these pathogens is very complicated and lacks standardization. This review provides a description of the main in vitro protocols so far assessed focusing on the exogenous phase, with oocyst viability and sporulation assays, and on the endogenous phase, with invasion and developmental assays in cell cultures and in ovo. An overview of these in vitro applications to screen both old and new remedies and to understand the relative mode of action is also discussed.

The impact of Bacillus subtilis DSM 32315 on the pathology, performance, and intestinal microbiome of broiler chickens in a necrotic enteritis challenge

It was hypothesized that dietary inclusion of Bacillus subtilis DSM 32315 could inhibit Clostridium perfringens induced necrotic enteritis (NE), thereby improving broiler performance. Male, d 0 chicks were randomly assigned 14 birds/pen, 11 pens/treatment in 3 treatments: a basal diet (control), a coccidiostat fed control (Narasin), and a direct fed microbial (DFM) B. subtilis DSM 32315 treatment. Necrotic enteritis was induced in all birds by oral inoculation of Eimeria maxima oocysts on d 12 and a virulent C. perfringens on d 16. Mortality was reduced (P < 0.001) in DFM and Narasin compared to control. DFM reduced (P < 0.001) feed conversion ratio (FCR) compared to control. Furthermore, DFM and Narasin reduced (P < 0.001) footpad lesions. The DFM was shown to increase (P < 0.05) Bacillus spp. and decrease (P < 0.05) C. perfringens in the ileum and cecum at several time points. To investigate microbiome changes in the cecum, digesta samples were analyzed with % guanine and cytosine (%G+C) microbial profiling which fractionates bacterial chromosomes based on the %G+C in DNA. The method revealed treatment profile peaks in low (27.0 to 34.5%), mid (40.5 to 54.0%), and high (59.0 to 68.0%) G+C fractions. 16S rRNA gene amplification and high throughput sequencing was conducted on each of these fractions in order to elucidate specific bacterial population differences. In the low and mid %G+C fractions, DFM had greater abundance of Lactobacillaceae family members (P = 0.03 and P = 0.01, respectively) and Lactobacillus salivarius (P = 0.04 and P = 0.01, respectively) than control or Narasin. Lactobacillus johnsonii was also greater in the low %G+C fraction compared to control and Narasin (P = 0.01). Lachnospiraceae (P = 0.04) and Ruminococcaceae (P < 0.01) in the mid %G+C fraction were reduced in the DFM compared to control. Positive alterations to the microbial populations in the gut of broilers may at least be a partial mechanism by which B. subtilis DSM 32315 reduced pathology and improved performance of broilers in the NE challenge.

Anticoccidial drugs of the livestock industry

Coccidiosis is a parasitic disease of a wide variety of animals caused by coccidian protozoa. The coccidia are responsible for major economic losses of the livestock industry. For example, the annual cost due to coccidiosis to the global poultry industry has been estimated to exceed US$ 3 billion annually. Currently available drugs for the control of this disease are either polyether ionophorous antibiotics that are derived from fermentation products, or synthetic compounds, produced by chemical synthesis. Unfortunately, no new drugs in either category have been approved for use for decades. Resistance has been documented for all those of the drugs currently employed and therefore the discovery of novel drugs with unique modes of action is imperative if chemotherapy is to remain the principal means to control this disease. This chapter aims to give an overview of the efficacy and mode of action of the current compounds used to control coccidiosis in livestock and provides a brief outlook of research needs for the future.

Disruption of a mitochondrial MutS DNA repair enzyme homologue confers drug resistance in the parasite Toxoplasma gondii

MutS homologues (MSHs) are critical components of the eukaryotic mismatch repair machinery. In addition to repairing mismatched DNA, mismatch repair enzymes are known in higher eukaryotes to directly signal cell cycle arrest and apoptosis in response to DNA-damaging agents. Accordingly, mammalian cells lacking certain MSHs are resistant to chemotherapeutic drugs. Interestingly, we have discovered that the disruption of TgMSH-1, an MSH in the pathogenic parasite, Toxoplasma gondii, confers drug resistance. Through a genetic selection for T. gondii mutants resistant to the antiparasitic drug monensin, we have isolated a strain that is resistant not only to monensin but also to salinomycin and the alkylating agent, methylnitrosourea. We have shown that this phenotype is due to the disruption of TgMSH-1 as the multidrug-resistance phenotype is complemented by a wild-type copy of TgMSH-1 and is recapitulated by a directed disruption of this gene in a wild-type strain. We have also shown that, unlike previously described MSHs involved in signalling, TgMSH-1 localizes to the parasite mitochondrion. These results provide the first example of a mitochondrial MSH that is involved in drug sensitivity and implicate the induction of mitochondrial stress as a mode of action of the widely used drug, monensin.

Polyether ionophores: broad-spectrum and promising biologically active molecules for the control of drug-resistant bacteria and parasites

BACKGROUND

As multidrug-resistant (MDR) pathogens continue to emerge, there is a substantial amount of pressure to identify new drug candidates. Carboxyl polyethers, also referred to as polyether antibiotics, are a unique class of compounds with outstanding potency against a variety of critical infectious disease targets including protozoa, bacteria and viruses. The characteristics of these molecules that are of key interest are their selectivity and high potency against several MDR etiological agents.

OBJECTIVE

Although many studies have been published about carboxyl polyether antibiotics, there are no recent reviews of this class of drugs. The purpose of this review is to provide the reader with an overview of the spectrum of activity of polyether antibiotics, their mechanism of action, toxicity and potential as drug candidates to combat drug-resistant infectious diseases.

CONCLUSION

Polyether ionophores show a high degree of promise for the potential control of drug-resistant bacterial and parasitic infections. Despite the long history of use of this class of drugs, very limited medicinal chemistry and drug optimization studies have been reported, thus leaving the door open to these opportunities in the future. Scifinder and PubMed were the main search engines used to locate articles relevant to the topic presented in the present review. Keywords used in our search were specific names of each of the 88 compounds presented in the review as well as more general terms such as polyethers, ionophores, carboxylic polyethers and polyether antibiotics.

Identification of new leishmanicidal peptide lead structures by automated real-time monitoring of changes in intracellular ATP

Leishmanicidal drugs interacting stoichiometrically with parasite plasma membrane lipids, thus promoting permeability, have raised significant expectations for Leishmania chemotherapy due to their nil or very low induction of resistance. Inherent in this process is a decrease in intracellular ATP, either wasted by ionic pumps to restore membrane potential or directly leaked through larger membrane lesions caused by the drug. We have adapted a luminescence method for fast automated real-time monitoring of this process, using Leishmania donovani promastigotes transfected with a cytoplasmic luciferase form, previously tested for anti-mitochondrial drugs. The system was first assayed against a set of well-known membrane-active drugs [amphotericin B, nystatin, cecropin A-melittin peptide CA(1-8)M(1-18)], plus two ionophoric polyethers (narasin and salinomycin) not previously tested on Leishmania, then used to screen seven new cecropin A-melittin hybrid peptides. All membrane-active compounds showed a good correlation between inhibition of luminescence and leishmanicidal activity. Induction of membrane permeability was demonstrated by dissipation of membrane potential, SYTOX trade mark Green influx and membrane damage assessed by electron microscopy, except for the polyethers, where ATP decrease was due to inhibition of its mitochondrial synthesis. Five of the test peptides showed an ED50 around 1 microM on promastigotes. These peptides, with equal or better activity than 26-residue-long CA(1-8)M(1-18), are the shortest leishmanicidal peptides described so far, and validate our luminescence assay as a fast and cheap screening tool for membrane-active compounds.

Synthesis and evaluation of a series of 1,4-diarylbutadienes for anticoccidial activity

During the course of a collaborative screening program, a set of 1-phenyl-4-pyridyl-butadienes was found to exhibit in vitro activity against Eimeria tenella in a cell-based assay. Activity was dependent on the chain length and degree of unsaturation of the linker between the two aryl groups as well as substitution of the pyridine moiety. Structure-activity relationship studies were subsequently conducted over a larger range of 1,4-diarylbutadienes in order to determine the scope of active compounds, to identify structural patterns governing activity and to enhance in vitro potency against E. tenella. In addition, the efficacy of many compounds for treating coccidiosis in chickens was measured by testing the ability of the compound to prevent or reduce intestinal and cecal lesions when administered by oral gavage. A few compounds in the series were identified that exhibited a moderate degree of in vitro and in vivo activity.

Flow cytometric analysis of Eimeria tenella sporozoite populations exposed to salinomycin sodium in vitro: a comparative study using light and electron microscopy and an in vitro sporozoite invasion-inhibition test

Eimeria tenella sporozoites exposed to 100, 70, 60 and 50 micrograms salinomycin sodium (SAL)/ml medium 199 at 41 degrees C and then stained with propidium iodide/fluorescein diacetate were analysed by means of flow cytometry (FCM). After 20 min exposure, they showed dose-dependent alterations in their size and shape, i.e. ballooning of most cells, and enhanced intracellular esterase activity as compared with untreated controls. After longer exposure periods (40 and 70 min), inflated cells gradually changed into shrivelled or crumpled, nonviable ones, thereby showing a gradual decrease in esterase activity and a gradual loss of membrane integrity (RFA+). As compared with untreated controls, sporozoites treated with 10 micrograms SAL/ml showed negligible RFA+ values (0.4%-2%), whereas those exposed to 1 and 0.1 microgram SAL ml and to the solvent dimethylsulfoxide (DMSO, 1%) did not, even after 70 min exposure. Slight to severe structural changes manifesting as an extremely wavy surface (1 microgram SAL/ml), vacuolization of the cytoplasm, distension or destruction of the mitochondrion and rupture of cell membranes (10 micrograms SAL/ml) were seen not only at higher SAL concentrations but also (rarely) at lower ones. The ability of sporozoites to invade primary chick-kidney cells was significantly inhibited by 70, 60 and 50 micrograms SAL/ml. In general, there were close relationships between findings obtained using FCM, electron microscopy and an invasion-inhibition test. The results indicate that FCM is a reliable and sensitive technique for characterizing the parasiticidal effects on and the possible mode of action of drugs in free coccidian sporozoites.

Ultrastructural studies of the effects of the ionophore lasalocid on Eimeria tenella in chickens

The ultrastructural development of Eimeria tenella was studied in experimentally infected chicks fed 90 ppm lasalocid, an ionophorous anticoccidial antibiotic. Drug treatment was timed to target-specific endogenous stages. At 6 h after infection, many sporozoites within the epithelium showed degradation as a result of drug action. Only a few intact sporozoites were seen. The drug caused outer-membrane blistering, large surface swellings and enlarged mitochondria in both first- and second-generation merozoites. No effect on the gamonts was discerned.

The effect of zinc bacitracin and roxarsone on performance of broiler chickens when fed in combination with narasin

Six trials were conducted at various locations to determine the response of broiler chickens to combinations of zinc bacitracin and roxarsone when fed in the presence of narasin. The addition of zinc bacitracin at 55 mg per kg significantly improved growth rate and feed utilization when data from all locations were combined. There was no effect of roxarsone fed at 50 mg per kg on BW or feed utilization, nor was there an interaction of roxarsone and zinc bacitracin on BW. There was a significant interaction of roxarsone and zinc bacitracin for feed utilization; addition of zinc bacitracin significantly improved feed utilization both in the presence and absence of roxarsone, but the improvement was greater in the absence of roxarsone.

The interactions between drugs and the parasite surface

The interrelationships between drugs and parasite surfaces are considered under the headings of (a) effects on membrane transport, (b) drug uptake mechanisms and (c) effects on surface morphology and function: praziquantel is discussed under a separate heading. The range of chemotherapeutic compounds that cause permeability changes and concomitant morphological disruption is discussed in terms of mode of drug action. Interpretation of the available data renders it difficult to identify the primary mode of action in the drugs considered. Drug uptake mechanisms are known for relatively few compounds; drug resistance as a function of drug acquisition is discussed. The role of the parasite surface as a specific drug target is argued.

Response of broiler chickens to dietary supplementation with roxarsone and bacitracin methylene disalicylate in diets containing narasin

Six trials were conducted at different locations to examine the response of broiler chickens to roxarsone and bacitracin in the form of bacitracin methylene disalicylate (BMD) in the presence of the anticoccidal narasin. All diets contained narasin (80 mg/kg) and were fortified with a factorial arrangement of roxarsone (0 to 50 mg/kg) and BMD (0 or 55 mg/kg). Broilers were grown to market weights with narasin and roxarsone removed from the diets for the final 5 days. Addition of both roxarsone and BMD resulted in significant (P less than .05) improvements in body weight and feed utilization. Response to roxarsone for feed utilization was influenced to some extent by the presence or absence of BMD. Although the response to roxarsone was always positive, the degree of response was lessened by the presence of BMD. This resulted in a significant (P less than .10) interaction between roxarsone and BMD for feed utilization but not for body weight.

Effect of ionophorous anticoccidials on invasion and development of Eimeria: comparison of sensitive and resistant isolates and correlation with drug uptake

Prophylactic levels of three ionophorous antibiotics, monensin, salinomycin, and lasalocid, were administered to groups of chickens and turkeys. All three ionophores markedly inhibited invasion of cecal tissues by sporozoites of ionophore-sensitive (IS) Eimeria tenella. Monensin and salinomycin also reduced invasion in turkeys by sporozoites of E. adenoeides, but lasalocid only minimally inhibited invasion. Invasion of ceca of monensin-medicated chickens was significantly greater by sporozoites of ionophore-resistant (IR) E. tenella than of the IS isolate. Concomitant experiments showed significant differences in [14C]monensin accumulation among IS and IR isolates of E. tenella. The decreased uptake of monensin by the IR isolates appeared to be accompanied by a decrease in responsiveness to the activity of monensin as well as to two other ionophores, salinomycin and narasin in cell culture. The amount of monensin, salinomycin or narasin required to inhibit development of E. tenella by 50% was 20 to 40 times higher for the IR isolates than for the IS ones. Collectively, the data suggest that differences in ionophore accumulation by IS and IR isolates of E. tenella might reflect differences in membrane chemistry and that these differences are responsible for the expressions of resistance that were observed in these studies. This expression of resistance appears to be common to all ionophores tested.

Control of chicken coccidiosis

Coccidiosis could potentially cause enormous economic loss to the poultry industry, especially in the production of broiler chickens (see Box 1). Losses are currently minimized by chemotherapeutic treatment but the effectiveness of many drugs seems to be declining. In this article, Peter Long and Tom Jeffers discuss the future for coccidial chemotherapy, and the potential for immunological control methods.

Drug resistance in avian coccidia (a review)

Drug resistance is now recognised as a major cause of the failure of drugs to control coccidiosis in the fowl. In this article, biological, biochemical and genetic aspects of resistance in Eimeria are reviewed and some of the problems that may limit progress in understanding the nature of resistance in coccidia are discussed.

The action of polyether ionophorous antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) in vivo and in vitro: study by light and electron microscopy

The effect of three polyether antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) was studied in vivo and in vitro by means of light and electron microscopy. It was found that these three drugs act against free merozoites, which are destroyed by bursting of the cell border (i.e. pellicle), endoplasmic reticulum and internal organelles even after very short exposure times (20 min) in media containing 1 ppm, 10 ppm or 100 ppm of these drugs. Sporozoites, however, survived these drug concentrations during an exposure time of 30 min (this would be sufficient to penetrate host cells and start development). Intracellular stages, which were situated in a parasitophorous vacuole within an intact host cell, were not attacked, apparently because these drugs are almost incapable of penetrating host cells. On the other hand, parasites (such as differentiated schizonts, gamonts) located within degenerating host cells showed slight disintegration, which did not necessarily led to their death. From these results it becomes clear why these polyether antibiotics have to be fed daily. Doses of 70 ppm salinomycin, 125 ppm monensin and 125 ppm lasalocid were found to bring about an equivalent protective effect against an infection with 40,000 Eimeria tenella oocysts.