Asynchronous capsule formation in the gastrointestinal tract of the prairie rattlesnake (Crotalus viridis viridis) induced by Mesocestoides sp. tetrathyridia

The prairie rattlesnake (Crotalus viridis viridis) was experimentally infected with tetrathyridia of Mesocestoides sp. Individual snakes were killed at 4 wk increments, and sections of the stomach, small intestine, large intestine and attached mesenteries were examined for nonencapsulated and encapsulated tetrathyridia. Capsule formation was asynchronous with 9 to 80% encapsulated metacestodes. The distribution of tetrathyridia in the wall of all segments of the gastrointestinal tract is presented as evidence that this metacestode is principally a tissue dwelling parasite.     

Schistocephalus solidus: establishment of tapeworms in sticklebacks--fast food or fast lane?

The penetration of the intestinal mucosal wall is supposed to be critical for helminth parasite infestation, but has rarely been analyzed in detail. We here studied the establishment process of Schistocephalus solidus tapeworms in their second intermediate host, the three-spined stickleback, from oral uptake after experimental exposure, to passage through the gastro-intestinal tract and arrival in the fish body cavity. Using histological techniques, we found tapeworms to penetrate the intestine within 14-24 h, spending most of the time in the stomach lumen and only a very short period in the intestine. Unexpectedly, tapeworms lost their outer layer, together with the cercomer, in the intestine lumen rather than later during intestine wall penetration. Once exposed, the underlying tegument with microtriches might serve to facilitate migration of the parasite into the body cavity.     

Alternative migration routes of Ascaris suum in the pig

Experiments were conducted to investigate possible alternative routes of extraintestinal migration of Ascaris suum larvae in the pig. Pigs were infected with A. suum via injection of newly hatched larvae into cecal veins (i.v.), into cecal lymph nodes (LN), or intraperitoneally (i.p.), and control animals were inoculated orally with infective eggs (p.o.). Two pigs per inoculation route were necropsied on days 1, 4, and 13 postinoculation. The numbers of liver lesions and the percentage of larvae recovered was considerably greater in pigs inoculated i.v. or p.o. on each necropsy day. However, irrespective of inoculation route, at least a proportion of larvae passed through the livers and were able to complete migration to the small intestine by day 13. The results indicate that larval penetration of the intestinal wall is not necessary for liver-lung migration and that passage through the liver may be favorable for migrating A. suum larvae, although a delayed arrival in the small intestine cannot be ruled out for larvae following alternative routes.     

A new host and locality record for Mesocestoides sp. tetrathyridia (Cestoidea: Cyclophyllidea), with a summary of the genus from snakes of the world

A new host and distribution record is reported for tetrathyridia of Mesocestoides sp. One of 5 (20%) Namib tiger snakes, Telescopus beetzi, from South Africa was infected. Numerous tetrathyridia were found encapsulated in mesentery attached to the small intestine. Morphological examination of tetrathyridia revealed absence of buds, multiple scoleces, or any other evidence of asexual proliferation. A summary of the snakes of the world reported as hosts of tetrathyridia of Mesocestoides sp. is presented.     

Adult worms of the rodent intestinal nematode,Strongyloides venezuelensis,successfully invade chick intestinal mucosa

In order to study the mucosal invasion of a rodent intestinal nematode in bird intestine, chicks were infected with the intestinal nematode of rodents, Strongyloides venezuelensis, by subcutaneous larva inoculation and adult worm implantation. No evidence was obtained for larvae reaching the lungs or the intestine after infective larva inoculation. Adult worms implanted in the small intestine invaded the mucosa and remained there at least for 24 h, whereas those implanted in the caecum were trapped by mucus, and did not invade the mucosa. Mucosal invasion of adult worms in the small intestine was confirmed by histological examination. The number of adult worms in the intestinal mucosal tissue dropped rapidly within the first 24 h, which was associated with infiltrating granulocytes around the worms. The present study suggests that S. venezuelensis adult worms are able to invade the intestinal tissue of chicks, which do not belong to the vertebrate class of its normal definitive host, but that they are eliminated rapidly by mucosal defense system of the bird.     

Plasma membrane-cell wall adhesion is required for expression of plant defense responses during fungal penetration

Fungal pathogens almost invariably trigger cell wall-associated defense responses, such as extracellular hydrogen peroxide generation and callose deposition, when they attempt to penetrate either resistant or susceptible plant cells. In the current study, we provide evidence that the expression of these defenses is dependent on adhesion between the plant cell wall and the plasma membrane. Peptides containing an Arg-Gly-Asp (RGD) motif, which interfered with plasma membrane-cell wall adhesion as shown by the loss of the thin plasma membrane-cell wall connections known as Hechtian strands, reduced the expression of cell wall-associated defense responses during the penetration of nonhost plants by biotrophic fungal pathogens. This reduction was associated with increased fungal penetration efficiency. Neither of these effects was seen after treatment with similar peptides lacking the RGD motif. Disruption of plant microfilaments had no effect on Hechtian strands but mimicked the effect of RGD peptides on wall defenses, suggesting that the expression of cell wall-associated defenses involves communication between the plant cell wall and the cytosol across the plasma membrane. To visualize the state of the plasma membrane-cell wall interaction during fungal penetration, we observed living cells during sucrose-induced plasmolysis. In interactions that were characterized by the early expression of cell wall-associated defenses, there was no change, or an increase, in plasma membrane-cell wall adhesion under the penetration point as the fungus grew through the plant cell wall. In contrast, for rust fungus interactions with host plants, there was a strong correlation between a lack of cell wall-associated defenses and a localized decrease in plasma membrane-cell wall adhesion under the penetration point. Abolition of this localized decreased adhesion by previous inoculation with a fungus that increased plasma membrane-cell wall adhesion resulted in reduced penetration by the rust fungus and induction of cell wall-associated defenses. These results suggest that rust fungi may induce a decrease in plasma membrane-cell wall adhesion as a means of disrupting the expression of nonspecific defense responses during penetration of host cells.     

Comparison between lead accumulation of Pomphorhynchus laevis (Palaeacanthocephala) in the intestine of chub (Leuciscus cephalus) and in the body cavity of goldfish (Carassius auratus auratus)

This experimental study assessed the role of the microhabitat in the uptake of metals by adult acanthocephalans. We examined the accumulation of lead by adult Pomphorhynchus laevis in the intestine of chub (Leuciscus cephalus) and compared it with that in goldfish, Carassius auratus auratus, in which the parasites penetrate the intestinal wall and enter the body cavity. Chub and goldfish experimentally infected with adult Pomphorhynchus laevis were exposed to 0.01 mg l(-1) Pb(2+) over 3 weeks. Lead was rapidly accumulated in the intestinal acanthocephalans reaching a mean concentration of 7.3 microg g(-1). This concentration was significantly greater than in the host muscle, liver and intestine and more than 730 times higher than the exposure concentration. Intraperitoneal P. laevis in goldfish exposed to lead did not accumulate the metal. Thus, it was conclusively shown that metal accumulation in acanthocephalans is associated with the intestinal location and does not occur in the body cavity.     

Early post-larval development of the endoparasitic platyhelminth Mesocestoides corti: trypsin provokes reversible tegumental damage leading to serum-induced cell proliferation and growth

Mesocestoides corti is a suitable in vitro model for studying the development of human endoparasitic platyhelminthes. Treatment with trypsin, supplemented with fetal bovine serum (FBS), induces M. corti development from larvae (tetrathyridia) to segmented adult worm; however, the role of this protease and of FBS in post-larval development induction remains unknown. To characterize the participation of trypsin enzymatic activity and of FBS in the induction of tetrathyridia growth and development, both stimuli were added to the larvae either together or sequentially. Additionally, specific inhibition of trypsin activity was also monitored. Finally, the effect of the enzyme on the parasite tegument as well as the proliferative activity and location of proliferating cells after induction of tetrathyridia development were also studied. We conclude that trypsin-induced tetrathyridia development to adult worm is FBS-dependent and that the effect of serum factors is dependent upon a previous trypsin-induced reversible damage to the larva tegument. In dividing and non-dividing tetrathyridia, proliferative activity of cells is mainly located within the apical massif in the anterior region and nerve cords of larvae, respectively. In tetrathyridia stimulated to develop to adult worms, an intense proliferative activity is evident along the nerve cords. Our results suggest that in natural infections the tetrathyridia tegument is temporally made permeable to growth factors by proteolytic enzyme activity in the intestine juice of the definitive host, thus leading to development to adult worms.     

Ultrastructure of infection-thread development during the infection of soybean by Rhizobium japonicum

The location and topography of infection sites in soybean (Glycine max (L.) Merr.) root hairs spot-inoculated with Rhizobium japonicum have been studied at the ultrastructural level. Infections commonly developed at sites created when the induced deformation of an emerging root hair caused a portion of the root-hair cell wall to press against an adjacent epidermal cell, entrapping rhizobia within the pocket between the two host cells. Infections were initiated by bacteria which became embedded in the mucigel in the enclosed groove. Infection-thread formation in soybean appears to involve degradation of mucigel material and localized disruption of the outer layer of the folded hair cell wall by one or more entrapped rhizobia. Rhizobia at the site of penetration are separated from the host cytoplasm by the host plasmalemma and by a layer of wall material that appears similar or identical to the normal inner layer of the hair cell wall. Proliferation of the bacteria results in an irregular, wall-bound sac near the site of penetration. Tubular infection threads, bounded by wall material of the same appearance as that surrounding the sac, emerge from the sac to carry rhizobia roughly single-file into the hair cell. Growing regions of the infection sac or thread are surrounded by host cytoplasm with high concentrations of organelles associated with synthesis and deposition of membrane and cell-wall material. The threads follow a highly irregular path toward the base of the hair cell. Threads commonly run along the base of the hair cell for some distance, and may branch and penetrate into subjacent cortical cells at several points in a manner analagous to the initial penetration of the root hair.     

The PEN1 syntaxin defines a novel cellular compartment upon fungal attack and is required for the timely assembly of papillae

Attack by the host powdery mildew Erysiphe cichoracearum usually results in successful penetration and rapid proliferation of the fungus on Arabidopsis. By contrast, the nonhost barley powdery mildew Blumeria graminis f. sp. hordei (Bgh) typically fails to penetrate Arabidopsis epidermal cells. In both instances the plant secretes cell wall appositions or papillae beneath the penetration peg of the fungus. Genetic screens for mutations that result in increased penetration of Bgh on Arabidopsis have recently identified the PEN1 syntaxin. Here we examine the role of PEN1 and of its closest homologue, SYP122, identified as a syntaxin whose expression is responsive to infection. pen1 syp122 double mutants are both dwarfed and necrotic, suggesting that the two syntaxins have overlapping functions. Although syp122-1 and the cell wall mur mutants have considerably more pronounced primary cell wall defects than pen1 mutants, these have relatively subtle or no effects on penetration resistance. Upon fungal attack, PEN1 appears to be actively recruited to papillae, and there is a 2-h delay in papillae formation in the pen1-1 mutant. We conclude that SYP122 may have a general function in secretion, including a role in cell wall deposition. By contrast, PEN1 appears to have a basal function in secretion and a specialized defense-related function, being required for the polarized secretion events that give rise to papilla formation.     

Collapsin-1/semaphorin D is a repellent for chick ganglion of Remak axons.

Chick collapsin-1/human semaphorin III/mouse semaphorin D is believed to guide the extension of specific axons by a repellent mechanism. Here we examine its role in the guidance of axons of the ganglion of Remak (Remak) in the developing chick intestine. Early in embryogenesis Remak axons extend parallel to, but do not enter, the intestine when collapsin-1 is expressed in the adjacent rectal wall. Remak axons later penetrate the peripheral portions of the rectal wall when collapsin-1 expression retreats from the outer muscle layer to the more internal submucosal and mucosal layers of the rectum. Extension of Remak neurites is repelled in vitro by rectum explants and also by 293T cells expressing collapsin-1. The rectal chemorepellent activity is blocked by anti-collapsin-1 antibodies. Our results suggest that collapsin-1 may help prevent Remak axons from projecting into the intestinal wall at early developmental times and later restricts Remak axon trajectories to the outer part of the intestinal muscle layer.     

Maternal transmission of asexually proliferative Mesocestoides corti tetrathyridia (Cestoda) in mice

Asexually proliferative Mesocestoides corti tetrathyridia were studied to test the hypothesis of in utero transmission in mice and define more clearly the path of transmammary transmission. In utero transmission was not observed in 132 fetuses (22 litters) taken by caesarean section from infected mothers. However, 19 of these mothers had tetrathyridia in their mammary glands at the time of operation, nine had worms in the uterine lumen, and one had a single worm in the maternal blood space of a placenta. No tetrathyridia were found in amniotic cavities. No infection was found in 32 young (7 litters) examined immediately after birth to infected mothers, but before nursing. No infection was found in 30 young (5 litters) removed from infected mothers before nursing and raised by uninfected fosters. Of 29 uninfected young (5 litters) allowed to nurse on infected mothers, 18 became infected. Whole mounts and sections of infected mammary glands showed proliferating tetrathyridia free in larger milk ducts and free and encapsulated in mammary parenchyma. These data suggest that maternal transmission of M. corti tetrathyridia in mice occurs primarily or perhaps exclusively by the transmammary route.     

Occurrence of tetrathyridia of Mesocestoides sp. (Cestoidea: Cyclophyllidea) in North American anurans (Amphibia)

A new host and geographic locality record is reported for tetrathyridia of Mesocestoides sp. in two species of ranid frogs (Rana berlandieri and R. pipiens) from Texas and New York, respectively. Tetrathyridia were found encapsulated in liver and mesenteries of the hosts. Morphological examination and experimental inoculation of these tetrathyridia into mice demonstrated the absence of capacity for asexual proliferation. Overall prevalence of infection was low in anurans from Arkansas, Texas and New York, but intensities can be generally high. In addition, a summary of frogs and toads from North America reported as hosts of tetrathyridia of Mesocestoides sp. is presented.     

Phocanema decipiens: Intestinal penetration in the laboratory rat

Larval Phocanema decipiens from cod muscles were fed singly or repeatedly to Sprague-Dawley rats and the condition of the rats was monitored. Rats given two larvae each week for 10 weeks were considered to be sensitized. “Sensitized” and “naive” rats were each exposed to larvae during laparotomy and the tissue pathology was examined from 5 hr to 14 days after penetration—no differences were found. This is evidence against the “two-hit hypothesis” of pathology resulting largely from prior sensitization of the host. The lesion was also comparable to that made in the intestine with a sterile pin. Tissue changes showed acute inflammation followed by monocyte infiltration and then fibrocytes and granulation tissue finally left a fibrotic scar. Penetration of larvae through exposed intestinal loops of anesthetized and laparotomized rats was described using a closed-circuit TV system. These records are related to potentiometric recordings of isolated larvae in which a mean mechanical force of 1 g was typical with a maximum of 3.5 g generated by the integrated movement of the whole body. A force of 10 to 12 g/mm² was needed to penetrate the mucosa, muscularis, and serosa. The movements of the host's intestine and the rhythmic probing of the larvae clearly facilitate penetration. The data are used to support the hypothesis that mechanical factors of the larval force and the strength of the intestine dominate the pathological potential of P. decipiens. It is concluded that P. decipiens presents a very small pathological potential to the intact human gastrointestinal tract.     

Paraquat effect on the bioelectric parameters of the rabbit small intestine and its in vitro penetration

The effect of paraquat (in concentrations of 10(-4) and 10(-3) mol/l) was studied on the bioelectric parameters of rabbit small intestine. A short-lasting rise in the potential difference (PD) and some decrease of tissue resistance (R) were observed, particularly after the higher concentration. These changes indicate stimulation of the transport function of the rabbit small intestine as a result of administration of this herbicide. Other tested parameters included determination of the rate of paraquat penetration (at concentration gradient 10(-3) mol/l) across the intestinal wall from the serosal side to the mucosal side and conversely. In the latter case three experimental models were used: first--complete intestinal wall, second--intestinal wall with the serosa stripped off, and third--intestinal wall with the mucosa and serosa removed. Differences were found in these rates depending on the model used. The importance of epithelial cells of the mucosa and subepithelial layers, and mesothelium of the serosa in limiting the penetration of bipirydylium herbicides is stressed.     

Protective effects of antibody against intestinal invasion by Escherichia coli

Seven Escherichia coli isolates from newborn calves with diarrhea were examined for enteropathogenic properties. One isolate penetrated into HeLa cells, four produced enterotoxin(s) and the remaining two possessed neither of these properties. Penetration of E. coli into HeLa cells was inhibited by antibody in bovine colostrum and in bovine and rabbit immune sera. The effective antibodies appeared to be mostly of the IgM class. The invasion by E. coli isolates was also examined by inoculation of the bacteria into the small intestine of E. coli-immunized and non-immunized guinea pigs. The isolate which penetrated into HeLa cells could penetrate the intestinal mucosa to be disseminated into various organs of non-immunized guinea pigs, but not of immunized guinea pigs, whereas no other isolates showed such pathogenicity in vivo. The inhibition of the invasion was observed when non-immunized guinea pigs were inoculated with the bacteria together with colostral or serum antibody. The results show the importance of antibody in the local defense mechanism against E. coli invasion.     

Bifidobacteria and human health: regulatory effect of indigenous bifidobacteria on Escherichia coli intestinal colonization

Bifidobacteria are assumed to exert colonization resistance to enteric pathogens. We associated C3H germfree mice with either Bifidobacterium longum or Escherichia coli or both strains and studied how they settled in the gut and the lymphoid organs as well as their effect on mucus composition. Within 24 hE. coli colonized the gut of germfree or B. longum ex-germfree mice. In contrast,B. longum was established in the intestine of E. coli ex-germfree mice only 1 month after inoculation whereas it colonized the germfree gut within 24 h. Although B. longum did not exert colonization resistance to E. coli, the establishing of bifidobacteria in the gut partly prevented changes in the E. coli cell wall. After colonization of the germfree or B. longum mono-associated mice, E. coli lipopolysaccharide exhibited a higher concentration of Kdo and the O-antigen side chain disappeared. A reduction in Kdo content was observed within 1 month in E. coli-B. longum diassociated mice whereas it remained at a high level in E. coli mono-associated mice. Association in a second step with B. longum led to Kdo reduction. Changes in E. coli LPS might be related to mucus modification. Inoculation of either bacterium led to a slow increase in mucus protein content which was however twice as high after E. coli implantation. Inoculation of B. longum in a second step led to a reduction in protein content before B. longum colonized the intestine at a high level suggesting that the protein concentration in the mucus was controlled by the host itself. A new glycoprotein of 200-230 kDa detected during the period preceeding colonization seemed to be broken down by B. longum. The resulting end product might participate in the restoration of E. coli LPS. Finally,B. longum inoculation led to the disappearance of E. coli from kidneys, liver, spleen and lung. The organs were cleared of E. coli before B. longum highly colonized the intestine suggesting that high intestinal colonization by B. longum was not required. Regulation of E. coli invasion seemed to depend on the ability of B. longum to stimulate the immune system.     

Interaction of Yersinia pseudotuberculosis with the epithelium of the small intestine in experimental infection

Some data showing specific ways of interaction of Yersinia pseudotuberculosis with the epithelium of the small intestinal mucosa have been received for the first time by using light microscopy of semithin sections. Comparative study of the lesion of the epithelium of different parts of rabbit small intestine by oral inoculation with Yersinia tuberculosis has expanded the ideas of the infection entry. It has been established for the first time that the most intensive penetration of the microorganisms into the epithelium of the mucous membrane takes place in the duodenum and jejunum. As the infected contents is evacuated via the intestinal tract, the Yersinia pathogenicity decreases, and in the ileum, the invasion of the microorganisms becomes less pronounced. It has been revealed that in pseudotuberculosis, there takes place a repeated dissemination of the infection in the intestinal tract because of decay of the involved enterocytes, which is of pathogenetic importance for the progress and outcome of the infection.     

The permeability of the barrier of the gastrointestinal tract for the macromolecules of polyethylene glycol-4000: an assessment of the mechanism and its reproducibility]

Polyethylene glycol (PEG)-4000 is proposed as a tracer of intestinal macromolecular permeability. The reproducibility of permeability testing with PEG-4000 and the mechanism of its penetration through intestinal mucosa were studied in adult rats. Permeability measurement for PEG-4000 was reproducible when repeated twice for 2 days. This makes it possible to repeat PEG-4000 permeability testing before and after any experimental impact on the intestine. I.p. administration of colchicine to rats (125 micrograms/100 g b. w.) significantly inhibited intestinal absorption of PEG-4000 fed to the animals 3 hours later. Hence, PEG-4000 penetration through the intestinal mucosa is mediated by the system of enterocyte cytoplasmic microtubules. Mucosal permeability for PEG-4000 may be consequently considered as a valuable model of permeability for protein macromolecules.