Application of analytical electron microscopic methods to investigate the function of spherites in the midgut of the larval antlion Euroleon nostras (Neuroptera: Myrmeleontidae)

This study presents an application of analytical electron microscopy in biology to investigate the chemical composition of the spherites and to elucidate the importance of these methods in the life sciences. The structure of the spherites in the midgut cells of first, second, and third instar larvae Euroleon nostras was investigated by a combination of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS), and energy filtering TEM (EFTEM). The structure and chemical composition of the spherites changed during the metamorphosis. In first larvae, the spherites are composed of amorphous, flocculent material, containing C, N, and O. In second larvae and third ones, the spherites have concentric layers of alternating electron-dense and electron-lucent material. In second larvae, Si, P, Ca, and Fe are accumulated in the spherite organic matrix, composed of C, N, and O. In the spherites of third larvae, additionally Al was found. Therefore, the spherites are thought to store organic compounds in all three larval stages of E. nostras and additionally inorganic compounds in second and third ones. In first larvae, spherites are present in the midgut cells; in second and third larvae, they are present in the cells of the midgut and in its lumen. It could be suggested that the spherites might be involved in the regulation of the appropriate mineral composition of the internal environment and could serve as the accumulation site of nontoxic waste materials that cannot be metabolized.     

Structural and ultrastructural features of the Malpighian tubules of Dolycoris baccarum (Linnaeus 1758), (Heteroptera: Pentatomidae)

The morphology and ultrastructure of the Malpighian tubules of Dolycoris baccarum were analyzed by scanning (SEM) and transmission (TEM) electron microscopy in order to determine their functional organization. The Malpighian tubules are compared with similar structures of other insects based on cell structure and functional organization. The Malpighian tubules of D. baccarum extend from the midgut–hindgut region of the digestive tract. The Malpighian tubules are divided into two regions: the proximal segment is short and flattened and the distal segment is long, stringy in shape and free in hemolymph. The tubules are generally long and narrow. There is a large number of trachea around the tubules. They consist of a single layer of epithelial cells. It is observed in the TEM observation that the epithelial cells have numerous microvilli at the apical side of the cells. At the basal side of the cells, there is a great number of membrane foldings and mitochondria among them. Besides some spherites, mitochondria, lysosome‐like bodies, and large or small granules can be distinguished in the cells. With this study, we aimed to demonstrate the ultrastructure of the Malpighian tubules of D. baccarum and differences or similarities with other species.     

Abdominal sensory equipment involved in external host discrimination in a solitary parasitoid wasp

Already parasitized hosts are often of poorer quality than healthy hosts. It is therefore usually advantageous for parasitoid females to recognize and reject them. Parasitized hosts can be identified on the basis of various physical or chemical marks present on the surface or inside the hosts or their surroundings in the case of concealed host. Here we studied host discrimination behaviors of females of a certain population of Pachycrepoideus vindemmiae, a solitary ectoparasitoid, which are known to reject large-sized parasitized hosts after an abdominal examination of their surface. We first investigated females' recognition behaviors of host parasitism status when confronted to small-sized hosts (Drosophila melanogaster pupae) as host size may influence the use of different cues for host selection. We showed that, in such a situation, females also discriminate parasitized hosts after an external host exploration with the tip of their ovipositor sheath (third valvulae). We then described the sense organs present on the different parts of the ovipositor by means of scanning and transmission electron microscopy analysis. As the extremity of the third valvulae bears only one type of sensilla that appears to be chemoreceptors, we considered these sensilla as highly likely to be involved in host discrimination in P. vindemmiae. To our knowledge, this is the first time that receptors located on the ovipositor sheath are described as implicated in host discrimination in parasitoid wasps. We discuss potential chemical markers that might be detected by these receptors.     

Application of elemental microanalysis to elucidate the role of spherites in the digestive gland of the helicid snail Chilostoma lefeburiana

In this case study we present an application of different analytical electron microscopic methods in biology, to elucidate their usefulness in such investigations. Using analytical electron microscopy, spherites in the digestive gland cells of the helicid snail Chilostoma lefeburiana were examined at three stages: just before the non-feeding period of over-wintering in November, in the middle of over-wintering in February and at its end in March. A detailed characterization of changes in the elemental composition of the spherites was characterized by a combination of transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy filtering TEM (EFTEM). During over-wintering, the spherites passed the following changes. Before over-wintering in November, they consisted of striking concentric layers of electron-dense and electron-lucent zones, while in February and March they showed clear empty zones between materials of different electron density. In November spherites, C, O, Ca, P, Cl, Fe, Si, Na, K, Mg and S were detected, whereas in February ones C, O, N, Cl, Si and S were found and only C, O, N, Si and Cl were detected in March spherites. It is suggested that the elements missing in February and March were used in different physiological processes during over-wintering, like (1) the maintenance of the appropriate elemental composition of the internal environment, (2) accumulation of non-toxic waste materials that cannot be metabolized and (3) avoiding potential intoxication by contamination with toxic metals.     

Histology and ultrastructure of Aedes albopictus larval midgut infected with Bacillus thuringiensis var. israelensis

Histological and ultrastrucutural alterations in the midgut of Aedes albopictus larvae infected with Bacillus thuringiensis var. israelensis (Bti) were observed by light and transmission electron microscopy (TEM). Two formulations of Bti were used: granulated and powder, with 0.2% active ingredient in 90 larvae of Ae. albopictus distributed in three containers containing 30 larvae each (one control group and two test groups). The midgut epithelium of the control group presented flattened and elongated cells with mace-shape with a narrow base. Midgut epithelium cells' surface was convex and had a large circular nucleus located in the median-apical portion of the cell. These cells also presented a basal lamina with a small accumulation of extracellular fibrous matrix, thus characterizing a basal membrane, with a muscle layer and a peritoneal membrane more externally. After Bti ingestion, the larvae stopped/slowed their natural movements down in 5 min. After 30 min approximately, the swimming movements stopped completely. Internally, the intestinal cells showed a disorganization of the basal processes, dilatation and fragmentation of the rough endoplasmic reticulum, with intense cytoplasmic vacuolization. There were concentric dense laminas accumulated in the cytoplasm, and these residual membranous bodies were seen greatly increased in size after 60 min. Mitochondria, fragments of rough endoplasmic reticulum and other remainder organelles were surrounded and segregated from the cytoplasm by exocytosis. This article reports the histopathological alterations in the midgut of Ae. albopictus after infection with Bti and contributes to a better understanding of the mode of action of this bacterial strain used as bioinsecticide against mosquito larvae.     

Elemental changes in the brain, muscle, and gut cells of the housefly, Musca domestica, exposed to heavy metals

The toxic effects of heavy metals on organisms are well established. However, their specific action at the cellular level in different tissues is mostly unknown. We have used the housefly, Musca domestica, as a model organism to study the toxicity of four heavy metals: copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb). These have been fed to larvae at low and high, semi-lethal concentrations, and their accumulation in the head, thorax, and abdomen was subsequently measured in adult flies. In addition, their impact on the cellular concentration of several elements important for cell metabolism-sodium (Na+), magnesium (Mg++), phosphorous (P), sulphur (S), chloride (Cl-) and potassium (K+)-were measured in neural cells, muscle fibers, and midgut epithelial cells. Our study showed that the heavy metals accumulate mainly in the abdomen, in which the concentrations of two of the xenobiotic metals, Cd and Pb, were 213 and 23 times more concentrated, respectively, than in controls. All the heavy metals affected the cellular concentration of light elements in all cell types, but the changes observed were dependent on tissue type and were specific for each heavy metal, and its concentration.     

Morphological organization of the dorsal protuberance of Linepithema humile (Mayr, 1868) ant's larvae (Hymenoptera, Formicidae)

The Argentine ant Linepithema humile is an important invasive species because of the levels of infestation that it can reach; however, there is little information about its presence, histological organization, and function of the dorsal protuberance, which is found exclusively in their larvae. The objective of this study was to describe it in L. humile through scanning electron microscopy and transmission electron microscopy, bringing information about this structure. The epidermis of these larvae have cuticles covering the whole body, and is formed by a sequence of overlapping lamellas where the inner ones were thicker and presented lower electron density, whereas the outer ones were thinner and highly electron dense. Pores or pore-like channels were not observed. A thick and acellular region composed of granular material was found under the cuticular layer. Out of this region, the flattened epidermic cells formed an epithelial layer. For the dorsal protuberance region, these cells become prismatic, and similarly to the cuticle, presents significant thickening. These cells presented extended microvilli, as well as a great amount of lamellar rough endoplasmic reticulum. Under this epithelium was observed a concentration of fat body cells, more numerous in the dorsal protuberance region. This study indicated that the dorsal protuberance present in the first segment of L. humile larvae has apparently no secretory function because no pores were found. This fact allowed to conclude that in L. humile larvae the dorsal protuberance would have the function to make it easier for the worker ants to carry them within the colony.     

Development beyond the gastrula stage and digestive organogenesis in the apple-snail <i>Pomacea canaliculata</i> (Architaenioglossa,Ampullariidae)

Development of Pomacea canaliculata from the gastrula stage until the first day after hatching is described. Trochophore embryos are developed after gastrulation, showing the prototroch as a crown of ciliated orange-brownish cells. However, no true veliger embryos are formed, since the prototroch does not fully develop into a velum. Afterward, the connection between the fore- and midgut is permeated and the midgut becomes full of the pink-reddish albumen, which is stored into a central archenteron’s lake, from where it is accumulated into the large cells forming the midgut wall (“giant cells”). Electron microscopy of giant cells in late embryos showed that albumen is engulfed by large endocytic vesicles formed between the irregular microvilli at the top of these cells. By the end of intracapsular development, giant cells become gradually replaced by two new epithelial cell types which are similar to those found in the adult midgut gland: the pre-columnar and the pre-pyramidal cells. Pre-columnar cells have inconspicuous basal nuclei and are crowned by stereocilia, between which small endocytic vesicles are formed. Pre-pyramidal cells have large nuclei with 2-3 nucleoli and show a striking development of the rough endoplasmic reticulum. The genesis of the three cell lineages (giant, pre-columnar and pre-pyramidal cells) is hypothetically attributed to epithelial streaks that occur at both sides of the midgut since early stages of development.     

Immunohistochemical study on the distribution of sodium-dependent vitamin C transporters in the respiratory system of adult rat

As vitamin C (L-ascorbic acid, VC) is known to be essential for many enzymatic reactions, the study on the transport mechanism of VC through cytoplasmic membrane is crucial to understanding physiological role of VC in cells and the respiratory system. In this regard, the study on the newly identified sodium-dependent VC transporters (SVCTs), SVCT1 and SVCT2, is required in organs that contain high concentration of VC. We have shown the distribution of SVCT proteins in the respiratory system, which has been reported to be one of the organs with a high concentration of VC, using immunohistochemical techniques. In the present study, intense SVCT immunoreactivities (IRs) were mainly localized in the respiratory system epithelial cells. In the trachea, both SVCT1 and 2 were localized in the psuedostratified ciliated columnar epithelium. In the terminal bronchiole, SVCT1 and 2 IRs were mainly observed in the apical portion of the simple columnar epithelium. In addition, SVCT IRs was localized within the cell membrane of some alveolar cells, even though we could not identify the exact cell types. These results provide the first evidence that intense SVCT1 and 2 IRs were found in the apical portion of the respiratory epithelial cells, suggesting that SVCT proteins in the apical portion could transport the reduced form of VC included in the airway surface liquid into the respiratory epithelial cells.     

Morphological characterization of the nymphs Rhipicephalus sanguineus ticks (Latreille, 1806) (Acari: Ixodidae). Description of the testes, integument, Malpighian tubules, and midgut on the detachment day

This study presents the morpho-histological and histochemical characterization of the testes, integument, Malpighian tubules, and midgut of engorged Rhipicephalus sanguineus nymphs on the detachment day, showing the morphological and physiological characteristics to this phase in the life cycle of these individuals. The testis is constituted by germinative cells (only spermatogonia) with large, round-shaped and strongly stained nuclei which are organized into cysts by a thin layer of somatic cells. The integument consists of a cuticle subdivided into epicuticle (lipoprotein) and procuticle (glycoproteic), and a layer of epithelial cells which present glycolipoprotein elements. The procuticle presents two distinct regions: the exocuticle (next to the epicuticle) and the endocuticle (next to the epithelial layer). The Malpighian tubules present a simple epithelium with small flat and/or cubic cells, which form its wall and delimitates a lumen full of lipoprotein material. The midgut consists of an epithelial wall formed by two types of digestive cells, spent cells and empty digest cells, and by generative cells supported by a basal lamina and a thin layer of muscular tissue. This study described the main organs of engorged nymphs of R. sanguineus, to generate information that can help researchers to better understand the biology of these ectoparasites; which is fundamental for the development of compounds that are less aggressive to the environment. In addition, if the immature stages of the ticks are controlled, the number of adult ticks able to cause damages to the animals--and to the man as well--is also under control.     

Structure and distribution of the Bacillus thuringiensis Cry4Ba toxin in lipid membranes

Bacillus thuringiensis Cry delta-endotoxins cause death of susceptible insect larvae by forming lytic pores in the midgut epithelial cell membranes. The 65 kDa trypsin activated Cry4Ba toxin was previously shown to be capable of permeabilizing liposomes and forming ionic channels in receptor-free planar lipid bilayers. Here, magnetic ACmode (MACmode) atomic force microscopy (AFM) was used to characterize the lateral distribution and the native molecular structure of the Cry4Ba toxin in the membrane. Liposome fusion and the Langmuir-Blodgett technique were employed for supported lipid bilayer preparations. The toxin preferentially inserted in a self-assembled structure, rather than as a single monomeric molecule. In addition, the spontaneous insertion into receptor-free lipid bilayers lead to formation of characteristic pore-like structures with four-fold symmetry, suggesting that tetramers are the preferred oligomerization state of this toxin.     

Ultrastructure of the Lyonet's glands in larvae of Diatraea saccharalis Fabricius (Lepidoptera: Pyralidae).

The Lyonet's gland is found in Lepidoptera larvae, close to the excretory duct of the silk gland. The role played by this gland is still uncertain. This work aims to describe the ultrastructure of the Lyonet's gland in Diatraea saccharalis larvae, offering suggestions regarding its possible function. The insects were reared under laboratory-controlled conditions. The glands were conventionally prepared for transmission (TEM) and scanning (SEM) electron microscopy. SEM showed that Lyonet's glands are paired small structures located in the ventral side of the head. They are composed by clustered long cells resembling leaves. Under TEM observations, each cell is surrounded by a thin basal lamina and contains large stellate nucleus. The cytoplasm presents large and empty canaliculi with small microvilli. The basal plasma membrane forms numerous infoldings where numerous and well-developed mitochondria are concentrated. The cytoplasmic membrane system is poorly developed. Our ultrastructural results suggest that the Lyonet's gland in D. saccharalis larvae may be involved in the uptake of small molecules from the hemolymph; no morphological evidences of macromolecules synthesis and secretion were noticed. The detection of nerve fibers in the gland suggest a neural control for the glandular cell function.     

Scanning electron microscope investigation on the process of healing of skin wounds in Cirrhinus mrigala

Present scanning electron microscope study, reports healing of excised skin wounds in Cirrhinus mrigala. Healing process of wounds, inflicted on head skin, using biopsy punch was observed at intervals—0 hour (h), 1, 2, 4, 6, 12 h, 1 day (d) 2 and 4 d. Accumulation of mucus in wound region within 1h after infliction of wound has been considered an immediate measure to provide protection to injured skin from microbial invasion and other external environmental hazards. On infliction of wound, mobilization of epithelial cells at wound edge is associated with disturbance of coaptive relationship of epithelial cells till original coaptive stability is reached. At 6–12 h appearance of epidermal ridge in region of contact of migrating fronts is due to piling up of epithelial cells. This is associated with cessation of migration of epithelial cells and their simultaneous continual arrival in the region. Speedy epithelialization of skin wounds in C. mrigala like in other fishes, compared to that of mammals and other higher vertebrates, is possibly facilitated owing to surrounding wet external environment. Microridges in initial stages of wound healing appear fragmented without particular orientation. Further, epithelial cells in epithelium in wound region and in region adjacent to wound elongate. These changes are associated with the stretching of epithelial cells indicating their streaming and migration, toward wound. Presence of superficial neuromasts, smallest functional units of lateral line system, a hydrodynamic sensory system, has been associated with important functional significance in fish.     

Toxicity of trifluralin herbicide in a representative of the edaphic fauna: Histopathology of the midgut of Rhinocricus padbergi (Diplopoda)

The aim of this study was to use the diplopod Rhinocricus padbergi as test organism to verify the possible toxic effects of the herbicide trifluralin in a representative of the edaphic fauna. Histological and histochemical techniques were applied in the midgut of the animals after exposure to different concentrations of trifluralin for 7 and 90 days (acute and subchronic exposure, respectively). The individuals from the control group did not present alterations to any of the exposures. In the acute exposure, the group exposed to a quarter and half of the field dose presented an accumulation of cytoplasmic granules in the hepatic cells; the field dose group presented an increase in the rate of epithelial renewal and the group exposed to double the field concentration presented an increase in the release of secretory vesicles. The subchronic response was obtained with the field dose and double field dose because the animals from a quarter and half groups did not survive until the end of the experiment. In both groups, the animals presented disruption of the epithelium and higher occurrence of hemocytes among the hepatic cells. The group exposed to double the field dose presented sites of cytoplasmic vacuolization, dilatation of the intercellular space, increase in the epithelial renewal, and release of secretory vesicles. The results alert for a careful use of this herbicide, since it promoted alterations in the midgut cells of the test organism used. Microsc. Res. Tech. 2012. © 2012 Wiley Periodicals, Inc.     

Epithelial cell polarity as reflected in enterocytes

Absorptive cells are the main cells present in the intestinal epithelium. The plasma membrane of these tall columnar cells reflects their high degree of polarization, by dividing into apical and basolateral domains with different compositions. The most characteristic structure of these cells consists of closely packed apical microvilli with the same height, looking like a brush, which is why they were named the brush border. The concentrated pattern of some apical markers observed in a restricted brush border domain shows that mature enterocytes are hyperpolarized epithelial cells: the filamentous brush border glycocalyx is anchored at the top of the microvilli and the annexin XIII is concentrated in the lower three fourths. Many studies have been carried out on the biosynthesis and intracellular pathway of domain markers. The results show clearly that the basolateral markers take a direct pathway from the trans-Golgi network to the basolateral membrane. However, the two apical pathways, one direct and one indirect pathway via the basolateral membrane, are used, depending on the apical protein involved. Efficient protein sorting and addressing are essential to the establishment and maintenance of cell polarity, on which the integrity of the epithelial barrier depends.     

ICP-MS法测定添食金属纳米颗粒后家蚕组织中的金属含量

为研究添食金属或金属氧化物纳米颗粒后家蚕体内金属元素含量的变化规律,建立了微波消解结合电感耦合等离子体质谱（ICP-MS）测定家蚕血液、中肠和丝腺中Cu和Ti元素含量的方法。实验中分别给5龄3天家蚕喂食浓度为500.00 mg/L纳米Cu和纳米TiO₂悬浮液;72 h后,剪破家蚕腹足收集家蚕血淋巴,并解剖收集中肠和丝腺。实验发现,Cu和Ti元素的标准曲线呈良好的线性关系,相关系数分别为0.999 95和0.999 89,两种元素的加标回收率均在96.6%～105.4%之间,相对标准偏差RSD小于3.7%。结果表明,对于纳米TiO₂实验组,家蚕血液和丝腺中的Ti元素含量与空白组相比变化不大,而中肠的Ti元素含量明显增加为（181.46±9.58） μg/g,约为空白组含量（63.39±6.44） μg/g的3倍(p＜0.05);在纳米Cu组中,家蚕血液中的Cu元素含量有轻微的变化,而中肠和丝腺中的含量增加较多,分别为（82.73±1.72） μg/g和（3.88±0.17） μg/g,约为空白组含量（11.68±0.46） μg/g和（1.77±0.26） μg/g 的7和2倍(p＜0.05)。该方法可准确地检测喂食纳米颗粒后,家蚕组织中的金属元素含量及其变化,可为进一步研究家蚕的纳米生物效应提供有力支持。     

Sewage sludge toxicity in edaphic organism: analysis of midgut responses in the diplopod Rhinocricus padbergi

Diplopods are agile saprophagous invertebrates with the ability to colonize several soil layers. They feed on waste and decaying organic matter, making the soil in which they are present better aerated and mineral‐enriched. Because of their habits, diplopods have been suggested to be used in studies to analyze possible toxic effects of impacted soils in edafic fauna. In that respect, this study aimed at checking the feasibility of using morphological analysis from millipede's midgut as a biomarker for soils exposed to sewage sludge from sewage treatment plants. Histological and histochemical techniques, applied to the species Rhinocricus padbergi's midgut, were used. Two sewage sludge samples were used; they were collected in two small towns in the countryside of São Paulo State. Both cities are part of the Piracicaba–Capivari–Jundiaí basin (PCJ‐1 and PCJ‐3). For 7 and 15‐day periods, the animals were exposed to 10% concentrations and crude sludge for the PCJ‐1sample and to 1, 10, and 50% concentrations and sludge for the PCJ‐3 sample. The material exposed to the PCJ‐1 sample showed an increase in the presence of cytoplasmic granules in both concentrations in all periods and a slight increase in the rate of epithelial renewal. The material of PCJ‐3 sample presented the same alterations observed in PCJ‐1 sample in higher frequence and over that high quantity of neutral polysaccharides in the hepatic cells layer. We can conclude that with the increase of sewage sludge concentrations tested, there is an increase in morphophysiologicals alterations frequencies found in the diplopods' midgut. Microsc. Res. Tech. 2012. © 2012 Wiley Periodicals, Inc.     

Isolation of epithelial cells,villi and crypts from small intestine of pigeons (<i>Columba livia</i>)

The isolation of viable enterocytes, villi and crypts from the small intestine of a feral bird (Columba livia) is important for performing physiological experiments in ecologically relevant processes of membrane transport. The effectiveness of mechanical disruption, enzymatic digestion and chelating agents were compared. The objectives were to isolate enterocytes, villi and crypts from the small intestine of young pigeons; to evaluate the viability of the isolated intestinal epithelial cells isolated; and to verify the integrity of enterocytes by biochemical features. Enzymatic and mechanical methods yielded both elongated columnar and spherical cells. With the chelating method villi and crypts were obtained. All methods produced a high yield of intestinal epithelial cells with about 50 % viability. Brush border enzymes (sucrase-isomaltase and alkaline phosphatase) activities were high and, as reported in chickens, they did not differ along the intestinal villus-crypt axis. Although the three methods have good viabilities, the enzymatic technique gives the best yield in cell number, while the chelating method provides the highest populations of morphologically distinctive villi and crypts.     

Proliferative characteristics of epithelial cells in the pregnant rat uterus

In the pregnant rat, killed at about mid gestation and 1 h after injection of tritiated thymidine, 40% of the cells in the epithelium lining the uterine lumen at the implantation site were labelled. Between implantation sites fewer than 20% of the surface epithelial cells were labelled. A series of rats was given tritiated thymidine on day 12 of pregnancy and killed at intervals in the next 30 h. A percentage labelled mitoses analysis of the epithelium between implantation sites (interconceptual) and within the implantation site (conceptual) showed that cells in either region spent 7 h in DNA synthesis and 1.5 h in the G₂ + ½ mitosis phases. The epithelial cells in the conceptual region spent 1.5 h in the G₁ + ½ mitosis phases whereas cells in interconceptual regions spent at least 11.5 h in these phases. The average cycle times of cells in conceptual regions was 10 h: in interconceptual regions minimum cycle time was 20 h and the average appeared to be considerably longer. The grain count of the epithelial cells in the conceptual region was rapidly reduced during the 30 h after injection of tritiated thymidine suggesting successive rounds of cell division. In contrast the grain count distribution of cells in interconceptual regions changed only slowly during this time. The percentage of labelled epithelial cells was determined in the animals killed up to 30 h after injection of tritiated thymidine. In both conceptual and interconceptual regions these percentages increased initially as labelled cells produced labelled progeny. In the conceptual region the increase was not maintained after 7 h as cells initially in G₁ divided to give unlabelled progeny. In the interconceptual region the increase in the percentage of labelled cells continued for 14 h; thereafter the percentage did not significantly alter. The interpretation of these results is discussed in relation to the differences in the kinetic characteristics of the epithelial cells in the two regions and in relation to the morphology of the epithelium lining the uterus during pregnancy.     

Interaction of bifidobacteria with the gut and their influence in the immune function

Bifidobacteria are predominant in the lumen of the large intestine and confer various health benefits on the host. They are also used in the preparation of new fermented milks (bioyogurts) or added to conventional yogurt to generate probiotic effects. The colonization of the gut by bacteria tends to be host specific due partly to the way in which bacteria adhere to the intestinal wall. Using a homologous strain of Bifidobacterium animalis in an experimental mouse model, we analyzed by immunofluorescence labelledbacteria and transmission electronic microscopy the importance of this bacterial interaction with epithelial an immune cells associated to the gut, and the effect of feeding of B. animalis in the immune response. It was able to adhere and interact with both small and large intestine. In spite of this interaction with the gut, no modifications in the immune state (secretory or systemic response) were observed.
A heterologous strain of Bifidobacterium adolescentis from human faeces, was neither uncapable of binding to the intestine, nor influence the immune system activation, when it was administered during 2, 5 or 7 consecutive days; we believe that using a homologous strain, oral tolerance is developed even when the microorganism interacts with the immune cells associated with the intestine. However, we cannot ignore the beneficial effect of these microorganisms, especially in the prevention of intestinal infections. We think that this property exerted by bifidobacteria is more related to other mechanisms such as competitive inhibition, acid production or others, than enhancement of the immune state.