Lactobacillus casei as a probiotic in malnourished Giardia lamblia-infected mice: a biochemical and histopathological study

Probiotics: an alternative anti-parasite therapy

This paper review about probiotic effects and mechanism of action against the gut and non-gut helminths and protozoan parasites. Gastrointestinal parasitic infections are considered a serious health problem and are widely distributed globally. The disease process which emanates from this parasite infection provides some of the many public and veterinary health problems in the tropical and sub-tropical countries. Prevention and control of the parasite disease is through antihelmintic and anti-protozoan drugs, but, due to the increasing emergence of such drug resistance, eradication of parasite infestation in human and livestock still lingers a challenge, which requires the development of new alternative strategies. The use of beneficial microorganisms i.e. probiotics is becoming interesting due to their prophylactic application against several diseases including parasite infections. Recent studies on the interactions between probiotics, parasites and host immune cells using animal models and in vitro culture systems has increased considerably and draw much attention, yet the mechanisms of actions mediating the positive effects of these beneficial microorganisms on the hosts remain unexplored. Therefore, the aim of the present review is to summarize the latest findings on the probiotic research against the gut and non-gut parasites of significance.

Efficacy of Lactobacillus taiwanensis S29 and Lactiplantibacillus plantarum S27 against tapeworm infection in Swiss Albino rats

Hymenolepis diminuta a zoonotic tapeworm infection in human remains an important cestode model for anthelmintic study as it display common clinical symptoms like other adult human tapeworms during heavy infestation. The use of Lactobacillus as a probiotic is an alternative to drugs which have increased in research and usage considerably during the last decade. The present study aims to determine the anthelmintic efficacy of two probiotics, L. taiwanensis strain S29 and L. plantarum strain S27 against H. diminuta in infected rat. Four groups of animals, each with six numbers were randomly chosen as the negative control (Group I), positive control (infected) (Group II) and the infected treated with two probiotics Group III and Group IV respectively. Another four groups (Group V-VIII) were selected and further subdivided into four sub-groups to investigate the development of larvae to adult during probiotics treatment. Worm burden, egg per gram were determined after treatment with these two probiotics. Furthermore, hematological assays and levels of biochemical markers were estimated, tissue damage was assayed through histological study and intestinal mitochondria detection was done. Worm sustainability reduced about 70-90% and EPG count decreased by 81-94% in probiotics treated groups. A significant level of unsuccessful establishment of larvae was observed in the developmental phase. Improvement in hematological parameter along with some biochemical parameters in the host were significantly observed after treatment with probiotics. The architecture damaged caused in the intestine and mitochondria density due to parasite infection improved significantly as that of control after probiotics treatment.

Giardia Antagonizes Beneficial Functions of Indigenous and Therapeutic Intestinal Bacteria during Malnutrition

Undernutrition in children commonly disrupts the structure and function of the small intestinal microbial community, leading to enteropathies, compromised metabolic health, and impaired growth and development. The mechanisms by which diet and microbes mediate the balance between commensal and pathogenic intestinal flora remain elusive. In a murine model of undernutrition, we investigated the direct interactions Giardia lamblia, a prevalent small intestinal pathogen, on indigenous microbiota and specifically on Lactobacillus strains known for their mucosal and growth homeostatic properties. Our research reveals that Giardia colonization shifts the balance of lactic acid bacteria, causing a relative decrease in Lactobacillus spp . and an increase in Bifidobacterium spp . This alteration corresponds with a decrease in multiple indicators of mucosal and nutritional homeostasis. Additionally, protein-deficient conditions coupled with Giardia infection exacerbate the rise of primary bile acids and susceptibility to bile acid-induced intestinal barrier damage. In epithelial cell monolayers, Lactobacillus spp . mitigated bile acid-induced permeability, showing strain-dependent protective effects. In vivo, L. plantarum, either alone or within a Lactobacillus spp consortium, facilitated growth in protein-deficient mice, an effect attenuated by Giardia , despite not inhibiting Lactobacillus colonization. These results highlight Giardia's potential role as a disruptor of probiotic functional activity, underscoring the imperative for further research into the complex interactions between parasites and bacteria under conditions of nutritional deficiency.

In Vivo Implications of Potential Probiotic Lactobacillus reuteri LR6 on the Gut and Immunological Parameters as an Adjuvant Against Protein Energy Malnutrition

The present study investigated the impact of probiotic Lactobacillus reuteri LR6 on the gut and systemic immunity using protein energy malnourished (PEM) murine model. Thirty male Swiss albino mice were divided into five groups: control (C), malnourished (M), probiotic fermented milk (PFM), skim milk (SM), and bacterial suspension (BS) with six mice per group. Group C was fed with conventional diet throughout the study while the other groups were fed with protein calorie restricted diet until the development of malnutrition. After development of malnutrition, group M was continued with the restricted diet while other groups were fed with re-nourished diet supplemented with PFM, SM, and BS for 1 week, respectively. Thereafter, mice were sacrificed and different histological, microbiological, and immunological parameters were studied. Probiotics feeding in PEM model as fermented product or bacterial suspension improved the intestinal health in terms of intact morphology of colonic crypts, normal goblet cells, and intact lamina propria with no inflammation in large intestine, absence of fibrosis, and no inflammation in spleen. The number of secretory IgA⁺ cells was significantly higher in group PFM and BS. Also, increase in the phagocytic percentage of the macrophages and bone marrow derived dendritic cells (DCs) were observed in the PFM and BS group in comparison to the group M. In comparison to the group M and SM, lactobacilli, bifidobacteria, and Firmicutes counts were significantly higher in the group PFM and BS. This study concludes that probiotic supplementation to re-nutrition diet could emerge as wonder therapeutics against PEM.

Disturbed gut microbiota and bile homeostasis in Giardia-infected mice contributes to metabolic dysregulation and growth impairment

Although infection with the human enteropathogen Giardia lamblia causes self-limited diarrhea in adults, infant populations in endemic areas experience persistent pathogen carriage in the absence of diarrhea. The persistence of this protozoan parasite in infants has been associated with reduced weight gain and linear growth (height-for-age). The mechanisms that support persistent infection and determine the different disease outcomes in the infant host are incompletely understood. Using a neonatal mouse model of persistent G. lamblia infection, we demonstrate that G. lamblia induced bile secretion and used the bile constituent phosphatidylcholine as a substrate for parasite growth. In addition, we show that G. lamblia infection altered the enteric microbiota composition, leading to enhanced bile acid deconjugation and increased expression of fibroblast growth factor 15. This resulted in elevated energy expenditure and dysregulated lipid metabolism with reduced adipose tissue, body weight gain, and growth in the infected mice. Our results indicate that this enteropathogen's modulation of bile acid metabolism and lipid metabolism in the neonatal mouse host led to an altered body composition, suggesting how G. lamblia infection could contribute to growth restriction in infants in endemic areas.

Bile Salt Hydrolases: At the Crossroads of Microbiota and Human Health

The gut microbiota has been increasingly linked to metabolic health and disease over the last few decades. Several factors have been suggested to be involved in lipid metabolism and metabolic responses. One mediator that has gained great interest as a clinically important enzyme is bile salt hydrolase (BSH). BSH enzymes are widely distributed in human gastrointestinal microbial communities and are believed to play key roles in both microbial and host physiology. In this review, we discuss the current evidence related to the role of BSHs in health and provide useful insights that may pave the way for new therapeutic targets in human diseases.

A Complementary Herbal Product for Controlling Giardiasis

Giardiasis is an intestinal protozoal disease caused by Giardia lamblia. The disease became a global health issue due to development of resistance to commonly used drugs. Since many plant-derived products have been used to treat many parasitic infestations, we aimed to assess the therapeutic utility of Artemisia annua (A. annua) for giardiasis. We showed that NO production was significantly reduced whereas serum levels of IL-6, IFN-γ, and TNF-α were elevated in infected hamsters compared to uninfected ones. Additionally, infection resulted in increased numbers of intraepithelial lymphocytes and reduced villi heights, goblet cell numbers, and muscularis externa thickness. We also showed that inducible NO synthase (iNOS) and caspase-3 were elevated in the intestine of infected animals. However, treatment with A. annua significantly reduced the intestinal trophozoite counts and IEL numbers, serum IL-6, IFN-γ, and TNF-α, while increasing NO and restoring villi heights, GC numbers, and ME thickness. Moreover, A. annua treatment resulted in lower levels of caspase-3, which indicates a protective effect from apoptotic cell death. Interestingly, A. annua therapeutic effects are comparable to metronidazole. In conclusion, our results show that A. annua extract is effective in alleviating infection-induced intestinal inflammation and pathological effects, which implies its potential therapeutic utility in controlling giardiasis.

Giardia spp. and the Gut Microbiota: Dangerous Liaisons

Alteration of the intestinal microbiome by enteropathogens is commonly associated with gastrointestinal diseases and disorders and has far-reaching consequences for overall health. Significant advances have been made in understanding the role of microbial dysbiosis during intestinal infections, including infection with the protozoan parasite Giardia duodenalis, one of the most prevalent gut protozoa. Altered species composition and diversity, functional changes in the commensal microbiota, and changes to intestinal bacterial biofilm structure have all been demonstrated during the course of Giardia infection and have been implicated in Giardia pathogenesis. Conversely, the gut microbiota has been found to regulate parasite colonization and establishment and plays a critical role in immune modulation during mono and polymicrobial infections. These disruptions to the commensal microbiome may contribute to a number of acute, chronic, and post-infectious clinical manifestations of giardiasis and may account for variations in disease presentation within and between infected populations. This review discusses recent advances in characterizing Giardia-induced bacterial dysbiosis in the gut and the roles of dysbiosis in Giardia pathogenesis.

Beyond Heat Stress: Intestinal Integrity Disruption and Mechanism-Based Intervention Strategies

The current climate changes have increased the prevalence and intensity of heat stress (HS) conditions. One of the initial consequences of HS is the impairment of the intestinal epithelial barrier integrity due to hyperthermia and hypoxia following blood repartition, which often results in a leaky gut followed by penetration and transfer of luminal antigens, endotoxins, and pathogenic bacteria. Under extreme conditions, HS may culminate in the onset of “heat stroke”, a potential lethal condition if remaining untreated. HS-induced alterations of the gastrointestinal epithelium, which is associated with a leaky gut, are due to cellular oxidative stress, disruption of intestinal integrity, and increased production of pro-inflammatory cytokines. This review summarizes the possible resilience mechanisms based on in vitro and in vivo data and the potential interventions with a group of nutritional supplements, which may increase the resilience to HS-induced intestinal integrity disruption and maintain intestinal homeostasis.

Pathogenesis and post-infectious complications in giardiasis

Giardia is an important cause of diarrhoea, and results in post-infectious and extra-intestinal complications. This chapter presents a state-of-the art of our understanding of how this parasite may cause such abnormalities, which appear to develop at least in part in Assemblage-dependent manner. Findings from prospective longitudinal cohort studies indicate that Giardia is one of the four most prevalent enteropathogens in early life, and represents a risk factor for stunting at 2 years of age. This may occur independently of diarrheal disease, in strong support of the pathophysiological significance of the intestinal abnormalities induced by this parasite. These include epithelial malabsorption and maldigestion, increased transit, mucus depletion, and disruptions of the commensal microbiota. Giardia increases epithelial permeability and facilitates the invasion of gut bacteria. Loss of intestinal barrier function is at the core of the acute and post-infectious complications associated with this infection. Recent findings demonstrate that the majority of the pathophysiological responses triggered by this parasite can be recapitulated by the effects of its membrane-bound and secreted cysteine proteases.

Animal Models of Undernutrition and Enteropathy as Tools for Assessment of Nutritional Intervention

: Undernutrition is a major public health problem leading to 1 in 5 of all deaths in children under 5 years. Undernutrition leads to growth stunting and/or wasting and is often associated with environmental enteric dysfunction (EED). EED mechanisms leading to growth failure include intestinal hyperpermeability, villus blunting, malabsorption and gut inflammation. As non-invasive methods for investigating gut function in undernourished children are limited, pre-clinical models are relevant to elucidating the pathophysiological processes involved in undernutrition and EED, and to identifying novel therapeutic strategies. In many published models, undernutrition was induced using protein or micronutrient deficient diets, but these experimental models were not associated with EED. Enteropathy models mainly used gastrointestinal injury triggers. These models are presented in this review. We found only a few studies investigating the combination of undernutrition and enteropathy. This highlights the need for further developments to establish an experimental model reproducing the impact of undernutrition and enteropathy on growth, intestinal hyperpermeability and inflammation, that could be suitable for preclinical evaluation of innovative therapeutic intervention.

Prophylactic Potential of Synbiotic (Lactobacillus casei and Inulin) in Malnourished Murine Giardiasis: an Immunological and Ultrastructural Study

Giardiasis is a re-emerging infectious disease with outbreaks reported globally specially in children and malnourished individuals leading to malabsorption, growth retardation, and severe diarrhea. Thus, in the present study, prophylactic administration of synbiotic as the functional food was used to assess its antigiardial potential in malnourished murine giardiasis. Interestingly, prior administration of synbiotic (Lactobacillus casei + inulin) even to malnourished-Giardia-infected mice led to increased body mass, small intestine mass, lactobacilli counts, and reduced severity of giardiasis as evident by decreased cyst and trophozoite counts. Synbiotic therapy further boosted the innate and acquired immune response resulting into increase in nitric oxide, antigiardial secretory IgA and IgG antibody levels along with IL-6 and IL-10 cytokines, and decreased levels of inflammatory TNF-α cytokine in both serum and intestinal fluid in malnourished-synbiotic-Giardia-infected mice compared with malnourished-Giardia-infected mice. More specifically, histopathological and scanning electron microscopy analysis of the small intestine also confirmed the modulatory potentials of synbiotic in malnourished-synbiotic-Giardia mice which had less cellular and mucosal damage compared with severely damaged, mummified, and blunted villi in malnourished-Giardia-infected mice. Taken together, this is the first experimental study to report that prior supplementation of synbiotic restored the gut morphology and improved the immune status of the malnourished-Giardia-infected mice, and could be considered as the prophylactic adjunct therapy for malnourished individuals.

The Anti-parasitic Effect of Probiotic Bacteria via Limiting the Fecundity of Trichinella Spiralis Female Adults

A potential protective effect of probiotic strains against zoonotic Trichinella spiralis infection was investigated in the framework of a new therapeutic strategy aimed at using probiotics to control parasitic zoonoses. The study was focused on the impact of six selected probiotic (bacteriocinogenic) strains on the intensity of T. spiralis infection and female fecundity ex vivo and in vitro. Bacterial strains of different origin (Enterococcus faecium EF55, Enterococcus faecium 2019 = CCM7420, Enterococcus faecium AL41 = CCM8558, Enterococcus durans ED26E/7, Lactobacillus fermentum AD1 = CCM7421, Lactobacillus plantarum 17L/1) were administered daily in a dose of 109 CFU/ml in 100 μl, and mice were infected with 400 T. spiralis larvae on day 7 of treatment. Female adults of T. spiralis were isolated on day 5 post infection (p.i.) and subsequently were used in fecundity test ex vivo. E. faecium CCM8558, E. faecium CCM7420 and E. durans ED26E/7 strains significantly reduced the number of adults in the intestine. The application of L. fermentum CCM7421, L. plantarum 17L/1, E. faecium CCM8558 and E. durans ED26E/7 caused a significant decrease in the number of muscle larvae. The treatment with E. faecium CCM8558 and E. durans ED26E/7 showed the highest inhibitory effect on female fecundity (94 %). The number of newborn larvae (NBL) was also significantly decreased after administration of L. fermentum CCM7421 and L. plantarum 17L/1 (80 %). A direct impact of probiotic strains on female reproductive capacity was examined in vitro in females isolated from untreated infected mice on day 5 p.i. A correlation was found between the inhibitory effect and the concentration of probiotic strains. The reduction effects of the strains manifested as follows: L. fermentum CCM7421 (93 %), E. faecium CCM8558, L. plantarum 17L/1, E. faecium EF55 (about 80 %), E. faecium CCM7420 and E. durans ED26E/7 (about 60 %).

Bile-Salt-Hydrolases from the Probiotic Strain Lactobacillus johnsonii La1 Mediate Anti-giardial Activity in Vitro and in Vivo

Giardia duodenalis (syn. G. lamblia, G. intestinalis) is the protozoan parasite responsible for giardiasis, the most common and widely spread intestinal parasitic disease worldwide, affecting both humans and animals. After cysts ingestion (through either contaminated food or water), Giardia excysts in the upper intestinal tract to release replicating trophozoites that are responsible for the production of symptoms. In the gut, Giardia cohabits with the host's microbiota, and several studies have revealed the importance of this gut ecosystem and/or some probiotic bacteria in providing protection against G. duodenalis infection through mechanisms that remain incompletely understood. Recent findings suggest that Bile-Salt-Hydrolase (BSH)-like activities from the probiotic strain of Lactobacillus johnsonii La1 may contribute to the anti-giardial activity displayed by this strain. Here, we cloned and expressed each of the three bsh genes present in the L. johnsonii La1 genome to study their enzymatic and biological properties. While BSH47 and BSH56 were expressed as recombinant active enzymes, no significant enzymatic activity was detected with BSH12. In vitro assays allowed determining the substrate specificities of both BSH47 and BSH56, which were different. Modeling of these BSHs indicated a strong conservation of their 3-D structures despite low conservation of their primary structures. Both recombinant enzymes were able to mediate anti-giardial biological activity against Giardia trophozoites in vitro. Moreover, BSH47 exerted significant anti-giardial effects when tested in a murine model of giardiasis. These results shed new light on the mechanism, whereby active BSH derived from the probiotic strain Lactobacillus johnsonii La1 may yield anti-giardial effects in vitro and in vivo. These findings pave the way toward novel approaches for the treatment of this widely spread but neglected infectious disease, both in human and in veterinary medicine.

Giardia Alters Commensal Microbial Diversity throughout the Murine Gut

Giardia lamblia is the most frequently identified protozoan cause of intestinal infection. Over 200 million people are estimated to have acute or chronic giardiasis, with infection rates approaching 90% in areas where Giardia is endemic. Despite its significance in global health, the mechanisms of pathogenesis associated with giardiasis remain unclear, as the parasite neither produces a known toxin nor induces a robust inflammatory response. Giardia colonization and proliferation in the small intestine of the host may, however, disrupt the ecological homeostasis of gastrointestinal commensal microbes and contribute to diarrheal disease associated with giardiasis. To evaluate the impact of Giardia infection on the host microbiota, we used culture-independent methods to quantify shifts in the diversity of commensal microbes throughout the gastrointestinal tract in mice infected with Giardia We discovered that Giardia's colonization of the small intestine causes a systemic dysbiosis of aerobic and anaerobic commensal bacteria. Specifically, Giardia colonization is typified by both expansions in aerobic Proteobacteria and decreases in anaerobic Firmicutes and Melainabacteria in the murine foregut and hindgut. Based on these shifts, we created a quantitative index of murine Giardia-induced microbial dysbiosis. This index increased at all gut regions during the duration of infection, including both the proximal small intestine and the colon. Giardiasis could be an ecological disease, and the observed dysbiosis may be mediated directly via the parasite's unique anaerobic fermentative metabolism or indirectly via parasite induction of gut inflammation. This systemic alteration of murine gut commensal diversity may be the cause or the consequence of inflammatory and metabolic changes throughout the gut. Shifts in the commensal microbiota may explain observed variations in giardiasis between hosts with respect to host pathology, degree of parasite colonization, infection initiation, and eventual clearance.

Interactions of Giardia sp. with the intestinal barrier: Epithelium, mucus, and microbiota

Understanding how intestinal enteropathogens cause acute and chronic alterations has direct animal and human health perspectives. Significant advances have been made on this field by studies focusing on the dynamic crosstalk between the intestinal protozoan parasite model Giardia duodenalis and the host intestinal mucosa. The concept of intestinal barrier function is of the highest importance in the context of many gastrointestinal diseases such as infectious enteritis, inflammatory bowel disease, and post-infectious gastrointestinal disorders. This crucial function relies on 3 biotic and abiotic components, first the commensal microbiota organized as a biofilm, then an overlaying mucus layer, and finally the tightly structured intestinal epithelium. Herein we review multiple strategies used by Giardia parasite to circumvent these 3 components. We will summarize what is known and discuss preliminary observations suggesting how such enteropathogen directly and/ or indirectly impairs commensal microbiota biofilm architecture, disrupts mucus layer and damages host epithelium physiology and survival.

Deconjugated Bile Salts Produced by Extracellular Bile-Salt Hydrolase-Like Activities from the Probiotic Lactobacillus johnsonii La1 Inhibit Giardia duodenalis In vitro Growth

Giardiasis, currently considered a neglected disease, is caused by the intestinal protozoan parasite Giardia duodenalis and is widely spread in human as well as domestic and wild animals. The lack of appropriate medications and the spread of resistant parasite strains urgently call for the development of novel therapeutic strategies. Host microbiota or certain probiotic strains have the capacity to provide some protection against giardiasis. By combining biological and biochemical approaches, we have been able to decipher a molecular mechanism used by the probiotic strain Lactobacillus johnsonii La1 to prevent Giardia growth in vitro. We provide evidence that the supernatant of this strain contains active principle(s) not directly toxic to Giardia but able to convert non-toxic components of bile into components highly toxic to Giardia. By using bile acid profiling, these components were identified as deconjugated bile-salts. A bacterial bile-salt-hydrolase of commercial origin was able to mimic the properties of the supernatant. Mass spectrometric analysis of the bacterial supernatant identified two of the three bile-salt-hydrolases encoded in the genome of this probiotic strain. These observations document a possible mechanism by which L. johnsonii La1, by secreting, or releasing BSH-like activity(ies) in the vicinity of replicating Giardia in an environment where bile is present and abundant, can fight this parasite. This discovery has both fundamental and applied outcomes to fight giardiasis, based on local delivery of deconjugated bile salts, enzyme deconjugation of bile components, or natural or recombinant probiotic strains that secrete or release such deconjugating activities in a compartment where both bile salts and Giardia are present.

The Microbiota Contributes to CD8+ T Cell Activation and Nutrient Malabsorption following Intestinal Infection with Giardia duodenalis

Giardia duodenalis is a noninvasive luminal pathogen that impairs digestive function in its host in part by reducing intestinal disaccharidase activity. This enzyme deficiency has been shown in mice to require CD8(+) T cells. We recently showed that both host immune responses and parasite strain affected disaccharidase levels during murine giardiasis. However, high doses of antibiotics were used to facilitate infections in that study, and we therefore decided to systematically examine the effects of antibiotic use on pathogenesis and immune responses in the mouse model of giardiasis. We found that antibiotic treatment did not overtly increase the parasite burden but significantly limited the disaccharidase deficiency observed in infected mice. Moreover, while infected mice had more activated CD8(+) αβ T cells in the small intestinal lamina propria, this increase was absent in antibiotic-treated mice. Infection also led to increased numbers of CD4(+) αβ T cells in the lamina propria and activation of T cell receptor γδ-expressing intraepithelial lymphocytes (IEL), but these changes were not affected by antibiotics. Finally, we show that activated CD8(+) T cells express gamma interferon (IFN-γ) and granzymes but that granzymes are not required for sucrase deficiency. We conclude that CD8(+) T cells become activated in giardiasis through an antibiotic-sensitive process and contribute to reduced sucrase activity. These are the first data directly demonstrating activation of CD8(+) T cells and γδ T cells during Giardia infections. These data also demonstrate that disruption of the intestinal microbiota by antibiotic treatment prevents pathological CD8(+) T cell activation in giardiasis.

Prebiotic inulin supplementation modulates the immune response and restores gut morphology in Giardia duodenalis-infected malnourished mice

Malnutrition induces a state of growth retardation and immunologic depression, enhancing the host susceptibility to various infections. In the present study, it was observed that prebiotic supplementation either prior or simultaneously with Giardia infection in malnourished mice significantly reduced the severity of giardiasis and increased the body and small intestine mass, along with increased lactobacilli counts in faeces compared with malnourished-Giardia-infected mice. More specifically, prebiotic supplementation significantly increased the levels of anti-giardial IgG and IgA antibodies and anti-inflammatory cytokines IL-6 and IL-10 and reduced the pro-inflammatory cytokine TNF-α, along with increased levels of nitric oxide in both the serum and intestinal fluid of malnourished-prebiotic-Giardia-infected mice compared with malnourished-Giardia-infected mice. Histopathology and scanning electron microscopy of the small intestine also revealed less cellular and mucosal damage in the microvilli of prebiotic-supplemented malnourished-Giardia-infected mice compared with severely damaged mummified and blunted villi of malnourished-Giardia-infected mice. This is the first study to report that prebiotic supplementation modulated the gut morphology and improved the immune status even in malnourished-Giardia-infected mice.

The Interplay of Host Microbiota and Parasitic Protozoans at Mucosal Interfaces: Implications for the Outcomes of Infections and Diseases

Infections by parasitic protozoans are largely neglected, despite threatening millions of people, particularly in developing countries. With descriptions of the microbiota in humans, a new frontier of investigation is developing to decipher the complexity of host-parasite-microbiota relationships, instead of the classic reductionist approach, which considers host-parasite in isolation. Here, we review with specific examples the potential roles that the resident microbiota can play at mucosal interfaces in the transmission of parasitic protozoans and in the progress of infection and disease. Although the mechanisms underlying these relationships remain poorly understood, some examples provide compelling evidence that specific components of the microbiota can potentially alter the outcomes of parasitic infections and diseases in humans. Most findings suggest a protective role of the microbiota, which might lead to exploratory research comprising microbiota-based interventions to prevent and treat protozoal infections in the future. However, these infections are often accompanied by an unbalanced microbiota and, in some specific cases, apparently, these bacteria may contribute synergistically to disease progression. Taken together, these findings provide a different perspective on the ecological nature of protozoal infections. This review focuses attention on the importance of considering polymicrobial associations, i.e., parasitic protozoans and the host microbiota, for understanding these human infections in their natural microbial context.

Therapeutic enhancement of newly derived bacteriocins against Giardia lamblia

Trials for identifying efficient anti-giardial agents are still ongoing. Nowadays, bacteriocins have attracted the attention as potential antimicrobial compounds. For the first time, the current study evaluated the therapeutic efficacy of bacteriocins derived from newly isolated Egyptian strains of probiotics Lactobacilli; L. acidophilus (P106) and L. plantarum (P164) against Giardia lamblia. Bacteriocins' efficacy was evaluated both in vitro; by growth inhibition and adherence assays, and in vivo; through estimation of parasite density, intestinal histopathological examination and ultrastructural analysis of Giardia trophozoites. In vivo bacteriocins' clinical safety was assessed. In vitro results proved that 50 µg of L. acidophilus bacteriocin induced reduction of the mean Giardia lamblia trophozoites by 58.3 ± 4.04%, while at lower concentrations of 10 and 20 µg of both L. acidophilus and L. plantarum, non significant reduction of the mean parasite density was achieved. In vitro trophozoites adherence was susceptible to the tested bacteriocins at all studied concentrations with variable degrees, while the highest adherence reduction was demonstrated using 50 µg of L acidophilus bacteriocin. In vivo, oral inoculation of 50 µg/mouse L. acidophilus bacteriocin for 5 successive days resulted in a noteworthy decline of the intestinal parasite density, along with amelioration of intestinal pathology of infected mice. Ultrastructural examination proved thatfive doses of L. acidophilus bacteriocin showed marked changes in cellular architecture of the trophozoites with evident disorganization of the cell membrane, adhesive disc and cytoplasmic components. This is the first reported study of the safe anti-giardial efficacy of L. acidophilus (P106) derived bacteriocin, hence highlighting its great promise as a potential therapeutic safe alternative to existing commercial drugs.

Potentiated anti-microsporidial activity of Lactobacillus acidophilus CH1 bacteriocin using gold nanoparticles

Through increased awareness and improved diagnostics, microsporidiosis has now been identified in a broader range of human populations; however current therapies are inconsistently effective. Recently, probiotics were determined as means for the control of intestinal parasitic infections through their secretory products; bacteriocins. This is the first study on the effect of bacteriocin produced by Lactobacillus acidophilus CH1 bacteriocin, with or without gold nanoparticles (Au-NPs), against intestinal microsporidiosis in immunosuppressed mice. Fecal and intestinal spore loads, besides viability, extrusion and infectivity of spores from treated animals were assessed. Results showed that the anti-microsporidial effects of bacteriocin were significantly potent. This efficiency was further potentiated upon conjugating bacteriocins with Au-NPs, as it induced a strikingly sustained reduction in fecal spore shedding after cessation of therapy by 1 week (94.26%). Furthermore, reduction in intestinal spore load was highest in bacteriocin/Au-NPs-inoculated mice (89.7%) followed by bacteriocin-inoculated group (73.5%). Spores encountered from stool of bacteriocin/Au-NPs group showed 92.4% viability, versus 93.7% in bacteriocin group. Spore extrusion and infectivity were most inhibited by exposure to bacteriocin/Au-NPs. Safety of bacteriocin/Au-NPs was also verified. Thus, considering the results of the present work, L. acidophilus CH1-derived bacteriocin can present a powerful safe therapy against intestinal microsporidiosis.

Increased expression of CD25, CD83, and CD86, and secretion of IL-12, IL-23, and IL-10 by human dendritic cells incubated in the presence of Toll-like receptor 2 ligands and Giardia duodenalis

Background

Effects of Giardia duodenalis on dendritic cell (DC) functions may contribute to the pathogenesis of chronic giardiasis. G. duodenalis lysate has been shown to inhibit the activation of murine DCs through the ligands of various Toll-like receptors (TLRs), including TLR2 and TLR4. Our study aimed at translating these findings to human DCs.

Findings

As described previously for murine DCs, also human DCs were only weakly activated by the parasite itself. LPS-stimulated DCs incubated in the presence of G. duodenalis lysate produced less IL-12/23p40 (p = 0.002), IL-12p70 (p = 0.011), and IL-23 (p = 0.004), but more IL-10 (p = 0.006) than cells incubated in the absence of the parasite. Concomitantly, the expression of CD25, CD83, CD86, and HLA-DR was reduced on G. duodenalis-incubated DCs as compared to control cells. In contrast, human DCs stimulated through TLR2 in combination with TLR1 or TLR6 and G. duodenalis lysate secreted significantly more IL-12/23p40 (p = 0.006), IL-23 (p = 0.002), and IL-10 (p = 0.014) than cells stimulated through TLR2 ligands alone. Ligands for TLR2/TLR1 or TLR2/TLR6 also induced enhanced extracellular expression of CD25, CD83, and CD86 (p < 0.05).

Conclusions

In contrast to murine DCs, human DCs incubated in the presence of G. duodenalis and stimulated through TLR2 show increased activation as compared to cells incubated in the absence of the parasite. Thus, TLR2 ligands, e.g., delivered by probiotic lactobacilli, might be beneficial in human giardiasis through an adjuvant effect on the induction of cellular immune responses against G. duodenalis.

Administration of kefir-fermented milk protects mice against Giardia intestinalis infection

Giardiasis, caused by the protozoan Giardia intestinalis, is one of the most common intestinal diseases worldwide and constitutes an important problem for the public health systems of various countries. Kefir is a probiotic drink obtained by fermenting milk with 'kefir grains', which consist mainly of bacteria and yeasts that coexist in a complex symbiotic association. In this work, we studied the ability of kefir to protect mice from G. intestinalis infection, and characterized the host immune response to this probiotic in the context of the intestinal infection. Six- to 8-week-old C75BL/6 mice were separated into four groups: controls, kefir mice (receiving 1 : 100 dilution of kefir in drinking water for 14 days), Giardia mice (infected orally with 4×10(7) trophozoites of G. intestinalis at day 7) and Giardia-kefir mice (kefir-treated G. intestinalis-infected mice), and killed at 2 or 7 days post-infection. Kefir administration was able to significantly reduce the intensity of Giardia infection at 7 days post-infection. An increase in the percentage of CD4(+) T cells at 2 days post-infection was observed in the Peyer's patches (PP) of mice belonging to the Giardia group compared with the control and kefir groups, while the percentage of CD4(+) T cells in PP in the Giardia-kefir group was similar to that of controls. At 2 days post-infection, a reduction in the percentage of B220-positive major histocompatibility complex class II medium cells in PP was observed in infected mice compared with the other groups. At 7 days post-infection, Giardia-infected mice showed a reduction in RcFcε-positive cells compared with the control group, suggesting a downregulation of the inflammatory response. However, the percentages of RcFcε-positive cells did not differ from controls in the kefir and Giardia-kefir groups. An increase in IgA-positive cells was observed in the lamina propria of the kefir group compared with controls at 2 days post-infection. Interestingly, the diminished number of IgA-positive cells registered in the Giardia group at 7 days post-infection was restored by kefir feeding, although the increase in IgA-positive cells was no longer observed in the kefir group at that time. No significant differences in CXCL10 expression were registered between groups, in concordance with the absence of inflammation in small-intestinal tissue. Interestingly, a slight reduction in CCL20 expression was observed in the Giardia group, suggesting that G. intestinalis might downregulate its expression as a way of evading the inflammatory immune response. On the other hand, a trend towards an increase in TNF-α expression was observed in the kefir group, while the Giardia-kefir group showed a significant increase in TNF-α expression. Moreover, kefir-receiving mice (kefir and Giardia-kefir groups) showed an increase in the expression of IFN-γ, the most relevant Th1 cytokine, at 2 days post-infection. Our results demonstrate that feeding mice with kefir reduces G. intestinalis infection and promotes the activation of different mechanisms of humoral and cellular immunity that are downregulated by parasitic infection, thus contributing to protection.

Oral Administration of the Probiotic Lactobacillus casei Ameliorates Gut Morphology and Physiology in Malnourished-Giardia intestinalis-Infected BALB/c Mice

Malnutrition reduces the host immunity and enhances the host susceptibility to various diseases. The present study describes the effect of oral administration of probiotic Lactobacillus casei to malnourished-Giardia-infected BALB/c mice with respect to surface alterations and brush border membrane enzyme activity of the small intestine. It was observed that probiotic feeding either prior to or simultaneously with Giardia infection to malnourished mice led to significantly enhanced activity of disaccharidases compared with malnourished and Giardia-infected mice. Scanning electron microscopy also revealed less mucosal damage in the villi of small intestine of probiotic-fed malnourished-Giardia-infected mice compared with completely damaged, mummified, or blunted villi of malnourished-Giardia-infected mice. The findings indicate that probiotics can be used as the prophylactic candidate in abrogating the gut and intestinal dissacharidases anamolies in malnourished hosts suffering from the intestinal diseases.

Persistent gut barrier damage and commensal bacterial influx following eradication of Giardia infection in mice

Background

Recent studies of Giardia lamblia outbreaks have indicated that 40–80% of infected patients experience long-lasting functional gastrointestinal disorders after parasitic clearance. Our aim was to assess changes in the intestinal barrier and spatial distribution of commensal bacteria in the post-clearance phase of Giardia infection.

Methods

Mice were orogastrically inoculated with G. lamblia trophozoites (strain GS/M) or pair-fed with saline and were sacrificed on post-infective (PI) days 7 (colonization phase) and 35 (post-clearance phase). Gut epithelial barrier function was assessed by Western blotting for occludin cleavage and luminal-to-serosal macromolecular permeability. Gut-associated, superficial adherent, and mucosal endocytosed bacteria were measured by agar culturing and were examined by fluorescence in situ hybridization. Intracellular bacteria cultured from isolated mucosal cells were characterized by 16S rDNA sequencing. Neutrophil-specific esterase staining, a myeloperoxidase activity assay, and enzyme-linked immunosorbent assays for cytokine concentrations were used to verify intestinal tissue inflammation.

Results

Tight junctional damage was detected in the intestinal mucosa of Giardia-infected mice on PI days 7 and 35. Although intestinal bacterial overgrowth was evident only during parasite colonization (PI day 7), enhanced mucosal adherence and endocytosis of bacteria were observed on PI days 7 and 35. Multiple bacterial strains, including Bacillus, Lactobacillus, Staphylococcus, and Phenylobacterium, penetrated the gut mucosa in the post-infective phase. The mucosal influx of bacteria coincided with increases in neutrophil infiltration and myeloperoxidase activity on PI days 7 and 35. Elevated intestinal IFNγ, TNFα, and IL-1β levels also were detected on PI day 35.

Conclusions

Giardia-infected mice showed persistent tight junctional damage and bacterial penetration, accompanied by mucosal inflammation, after parasite clearance. These novel findings suggest that the host’s unresolved immune reactions toward its own microbiota, due to an impaired epithelial barrier, may partly contribute to the development of post-infective gut disorders.

Giardia: both a harmless commensal and a devastating pathogen

The highly prevalent protozoan Giardia lamblia is an enteropathogen that can be asymptomatic in some individuals, while leading to persistent diarrhea and substantial morbidity in others. In this issue of the JCI, Bartelt et al. describe a mouse model of the disease and investigate the contribution of coincident malnutrition with the development of symptomatic infection. This work in part explains how Giardia infection can lead to growth retardation, and may offer insights that guide future therapeutic strategies.

Persistent G. lamblia impairs growth in a murine malnutrition model

Giardia lamblia infections are nearly universal among children in low-income countries and are syndemic with the triumvirate of malnutrition, diarrhea, and developmental growth delays. Amidst the morass of early childhood enteropathogen exposures in these populations, G. lamblia–specific associations with persistent diarrhea, cognitive deficits, stunting, and nutrient deficiencies have demonstrated conflicting results, placing endemic pediatric giardiasis in a state of equipoise. Many infections in endemic settings appear to be asymptomatic/ subclinical, further contributing to uncertainty regarding a causal link between G. lamblia infection and developmental delay. We used G. lamblia H3 cyst infection in a weaned mouse model of malnutrition to demonstrate that persistent giardiasis leads to epithelial cell apoptosis and crypt hyperplasia. Infection was associated with a Th2-biased inflammatory response and impaired growth. Malnutrition accentuated the severity of these growth decrements. Faltering malnourished mice exhibited impaired compensatory responses following infection and demonstrated an absence of crypt hyperplasia and subsequently blunted villus architecture. Concomitantly, severe malnutrition prevented increases in B220+ cells in the lamina propria as well as mucosal Il4 and Il5 mRNA in response to infection. These findings add insight into the potential role of G. lamblia as a "stunting" pathogen and suggest that, similarly, malnourished children may be at increased risk of G. lamblia– potentiated growth decrements.

Probiotic Lactobacillus rhamnosus GG modulates the mucosal immune response in Giardia intestinalis-infected BALB/c mice

BACKGROUND

Gut homeostasis can be altered by the oral administration of health-promoting microorganisms, namely probiotics that are known to reinforce the host immune response.

AIM

The aim of this study was to elucidate the immunomodulatory effect of orally administered probiotic Lactobacillus rhamnosus GG (LGG) in Giardia-infected mice.

METHODS

BALB/c mice were fed orally with probiotic LGG either 7 days prior to or simultaneously with the challenge dose of Giardia trophozoites. The administration of the probiotic was continued for 25 days, and immunomodulatory potentials in terms of secretory immunoglobulin A (IgA) levels, CD8+ and CD4+ T lymphocytes, and expression of pro-inflammatory [tumor necrosis factor-alpha, interferon-gamma (INF-γ)] and anti-inflammatory cytokines [interleukin (IL)-4, IL-6, IL-10] were studied.

RESULTS

Oral feeding of LGG prior to or simultaneously with the test dose of Giardia seems to have modulated both arms (humoral and cellular) of the mucosal immune system since a significant increase in the levels of specific secretory IgA antibody, IgA+ cells, and CD4+ T lymphocytes were observed in contrast with the decreased percentage of cytotoxic CD8+ T lymphocytes. The stimulated mucosal immune response in probiotic fed Giardia-infected mice was further correlated with the enhanced levels of anti-inflammatory cytokines IL-6 and IL-10 and reduced levels of pro-inflammatory cytokine INF-γ.

CONCLUSIONS

This is the first study to show that oral administration of the effective probiotic LGG to Giardia infected mice could be used as a bacterio-therapy that restores the normal gut microflora and modulates the mucosal immune response.

Comparative therapeutic effect of probiotic Lactobacillus casei alone and in conjunction with antiprotozoal drugs in murine giardiasis

Various antiprotozoal drugs have been used to counteract the spread of giardiasis. However, due to increase in resistance to these compounds, there is an urgent need to find a natural biocompatible product to fight the pathogen in more healthy and effective way. The present study was designed to compare the therapeutic effect of probiotic Lactobacillus casei alone and in conjunction with antiprotozoal drugs on the outcome of giardiasis in murine model. BALB/c mice were challenged with Giardia intestinalis trophozoites, and 1 day after infection, these mice were treated with either probiotic alone or in conjunction with antiprotozoal drugs. Cyst, trophozoite, and lactobacilli counts were monitored vis-a-vis histopathological alterations in the small intestine. It was found that albendazole administered orally 1 day after Giardia infection was the most effective antiprotozoal drug among albendazole, tinidazole, metronidazole, and nitazoxanide. It reduced both the severity and duration of giardiasis. More specifically, oral administration of the probiotic L. casei in conjunction with albendazole further reduced the Giardia infection as was evident by the restored normal gut morphology. This suggests that probiotics and antiprotozoal drugs in combination may be the better alternative therapy for treatment of gastrointestinal diseases and enhanced recovery.

Lactobacillus rhamnosus GG antagonizes Giardia intestinalis induced oxidative stress and intestinal disaccharidases: an experimental study

The present study describes the in vivo modulatory potential of Lactobacillus rhamnosus GG (LGG), an effective probiotic, in Giardia intestinalis-infected BALB/c mice. Experimentally, it was observed that oral administration of lactobacilli prior or simultaneous with Giardia trophozoites to mice, efficiently (p < 0.05) reduced both the severity and duration of giardiasis. More specifically, probiotics fed, Giardia-infected mice, showed a significant increase in the levels of antioxidants [reduced glutathione (GSH) and superoxide dismutase (SOD)] and intestinal disaccharidases [sucrase and lactase] and decreased levels of oxidants in the small intestine, in comparison with Giardia-infected mice. Histopathological findings also revealed almost normal cellular morphology of the small intestine in probiotic-fed Giardia-infected mice compared with fused enterocytes, villous atrophy and increased infiltration of lymphocytes in Giardia-infected mice. The results of the present study has shed new light on the anti-oxidative properties of LGG in Giardia mediated tissue injury, thereby suggesting that the effects of probiotic LGG are biologically plausible and could be used as an alternative microbial interference therapy.

Interactions between parasites and microbial communities in the human gut

The interactions between intestinal microbiota, immune system, and pathogens describe the human gut as a complex ecosystem, where all components play a relevant role in modulating each other and in the maintenance of homeostasis. The balance among the gut microbiota and the human body appear to be crucial for health maintenance. Intestinal parasites, both protozoans and helminths, interact with the microbial community modifying the balance between host and commensal microbiota. On the other hand, gut microbiota represents a relevant factor that may strongly interfere with the pathophysiology of the infections. In addition to the function that gut commensal microbiota may have in the processes that determine the survival and the outcome of many parasitic infections, including the production of nutritive macromolecules, also probiotics can play an important role in reducing the pathogenicity of many parasites. On these bases, there is a growing interest in explaining the rationale on the possible interactions between the microbiota, immune response, inflammatory processes, and intestinal parasites.

Restoration of anthropometric, biochemical and histopathological alterations by Lactobacillus casei supplementation in Giardia intestinalis infected renourished BALB/c mice

The present study describes the in vivo ameliorating effect of Lactobacillus casei supplementation in renourished Giardia intestinalis infected BALB/c mice. It was observed that daily administration of probiotic 7 days prior to Giardia-infection to renourished mice, efficiently reduced the excretion of Giardia cysts and trophozoite counts, along with significant increased fecal lactobacilli counts compared with Giardia-infected mice. It was also observed that oral feeding of probiotic to renourished-Giardia-infected mice abrogated all the anthropometric and biochemical anomalies. Histologically, morphological and cellular alteration of microvillus membrane integrity revealed that probiotic administration further ameliorated the mucosal damage in renourished-probiotic-Giardia-infected mice compared to severe microvillus atrophy, oedematous, vacuolated epithelial cells and ileitis in renourished-Giardia and Giardia-infected mice. Thus, it is suggested that probiotic used as the functional food helps in restoration of anthropometric, biochemical alterations and atrophied gut by enhancing the goblet cells and reducing the giardiasis.

Changes in serum zinc levels associated with giardiasis and dietary zinc intake in mice

The association of giardiasis with the malabsorption of zinc remains controversial. This study investigated changes in serum zinc levels in Giardia-infected mice subjected to different dietary zinc regimens. Thirty-five mice (strain C(3)H/H(e)J) were randomly categorized into two groups. The first group was inoculated with 5 × 10(6) Giardia trophozoites (n = 18), and the second group remained Giardia free (n = 17). Each group (Giardia infected and Giardia free) was randomly classified into three subgroups and given low (9 mg Zn/kg), normal (33 mg Zn/kg), and high levels (288 mg Zn/kg) of dietary zinc over a 2-week period for acclimation. Fourteen days post-Giardia infection, all of the mice were euthanized and blood samples were collected. The number of trophozoites was quantified (hematocytometer), and serum zinc levels were determined via atomic absorption spectrophotometry. Significant increases in the median weights were only found in the Giardia-free mice (p < 0.05). A higher final median weight was found in the Giardia-free group when compared with that of the Giardia-infected group given low dietary zinc (p = 0.013). In the Giardia-infected group with low dietary zinc, the geometric mean of trophozoites was 3,498 ± 101 (SE) per milliliter. The Giardia-infected group had lower serum zinc levels than did the Giardia-free group with the high dietary zinc regimens (p < 0.05). Our results are consistent with studies among human populations, but further studies are required to elucidate the actual mechanism governing the zinc-giardiasis interaction.

Probiotics for the control of parasites: an overview

Probiotics are defined as live organisms, which confer benefits to the host. Their efficiency was demonstrated for the treatment of gastrointestinal disorders, respiratory infections, and allergic symptoms, but their use is mostly limited to bacterial and viral diseases. During the last decade, probiotics as means for the control of parasite infections were reported covering mainly intestinal diseases but also some nongut infections, that are all of human and veterinary importance. In most cases, evidence for a beneficial effect was obtained by studies using animal models. In a few cases, cellular interactions between probiotics and pathogens or relevant host cells were also investigated using in vitro culture systems. However, molecular mechanisms mediating the beneficial effects are as yet poorly understood. These studies indicate that probiotics might indeed provide a strain-specific protection against parasites, probably through multiple mechanisms. But more unravelling studies are needed to justify probiotic utilisation in therapeutics.