The ultrastructure of the neonatal pig colon

Enterobacter sakazakii invasion in human intestinal Caco-2 cells requires the host cell cytoskeleton and is enhanced by disruption of tight junction

Enterobacter sakazakii is an opportunistic pathogen that causes systemic bacteremia and meningitis with high mortality, and powdered infant formula is a frequent source of this bacterium. However, the mechanisms that this organism uses to invade and translocate through the intestinal barrier are unknown. Using Caco-2 epithelial cells, we were able to demonstrate penetration of E. sakazakii and to determine invasion-associated properties. We found that E. sakazakii entry and invasion were dependent on the exposure time and multiplicity of infection and required bacterial de novo protein synthesis but was independent of cell polarity in the presence of tight junctions. Moreover, the presence of actin filaments and microtubule structures was required, and disruption of the tight junction significantly enhanced the initial association with Caco-2 cells and the efficiency of invasion, which provides a possible explanation for the preferential occurrence of this infection in babies and neonates. This is the first description of E. sakazakii invasion of host intestinal cells, and our findings suggest that this emerging pathogen employs a novel invasion mechanism for development of systemic infection.

Changes in tissue nucleic acid content and mucosal morphology during intestinal development in pouch young of the tammar wallaby (Macropus eugenii eugenii)

DNA and RNA content and the timing of development of various histological features in the small and large intestine of in-pouch tammar wallabies (Macropus eugenii eugenii) of various ages were measured. A significant decline in gut tissue DNA concentrations and increase in the RNA/DNA ratios over 300 days postpartum indicated that the early postnatal increase in gut tissue mass resulted largely from hypertrophy. Mean duodenal and ileal villus height and crypt depth were significantly greater for in-pouch young aged >100 days compared with those <100 days and were significantly greater in the duodenum than in the ileum. Goblet cells appeared more slowly during development and were fewer in number in the duodenal than in the colonic mucosa. The numbers of mucin-secreting duodenal goblet cells were greater in pouch young aged >100 days than in young aged <100 days. The colonic mucosa exhibited no villi or villus-like folds. Colonic crypt depth increased uniformly with age.

Prenatal and postnatal development of the large intestine in the insectivore Suncus murinus, the laboratory shrew

Development of the large intestine in the insectivore Suncus murinus (the laboratory shrew) was investigated from day 21 to 30 of gestation and from birth to 20 days of age. Two days before birth, the stratified epithelium in the large intestine changed into a single layer. Although neither villi nor villus-like structures were ever present, fissures, corresponding to openings of the crypts, appeared on the mucosal surface before birth. These increased in number as well as in width and depth, connected with each other, and gave the mucosal surface a ridge-like appearance by 20 days of age. An elevation containing submucosae appeared shortly after birth and formed a large circular fold during the neonatal period. Goblet cells were the predominant epithelial cell type. Individual epithelial cells were mature-looking a few days before birth; goblet cells contained numerous mucous globules and absorptive cells possessed well-developed organelles. However, although goblet cells increased in number and exhibited active mucous-releasing forms after birth, absorptive cells never showed morphologic evidence of active endocytosis, such as apical endocytotic complexes and large supranuclear vacuoles. Each epithelial cell was similar in ultrastructure to that of the adult shortly after birth.

Structural and enzymatic changes during colonic maturation in the fetal and suckling rat

To assess correlations between cellular differentiation and enzymatic maturation in the developing rat colon, tissue from fetal, suckling, weanling, and adult rats was analyzed by electron microscopy and assayed for lactase, alkaline phosphatase, and sodium-potassium-stimulated adenosine triphosphatase activities. The proximal and distal colon were analyzed independently at all ages. All three enzymes were detected in the fetal colon when the cells were highly undifferentiated. Postnatally, significant regional differences in cellular ultrastructure appeared, only some of which were directly paralleled by enzymatic changes. Each enzyme had a distinct region-specific developmental pattern. Lactase and sodium-potassium-stimulated adenosine triphosphatase were significantly enhanced at birth, decreasing to adult levels by 15 days postnatal. Regional differences were present, but the patterns were similar. These patterns did not parallel the increase in microvillar height and number and basolateral interdigitations of the surface columnar cells, the structural correlates of lactase, and sodium-potassium-stimulated adenosine triphosphatase, respectively. In contrast, developmental changes in alkaline phosphatase activity paralleled structural maturation, at least in part. The activity levels in the distal colon did not change significantly with age and few major structural changes were noted. In the proximal colon, activity increased markedly after birth, and after 10 days decreased rapidly to adult levels, a pattern that coincided with the transient appearance of villi and specialized cells with apical tubules and vesicles known to have alkaline phosphatase activity. The results show age- and region-related changes in cellular ultrastructure and enzymatic activities, only some of which appear to be directly correlated.

[Optical and scanning electron microscopic study of the structural development of the cecum and colon walls in the rabbit (Oryctolagus cuniculus L.) during the perinatal period]

The study, through optical and scanning microscopy, of various developmental stages, from the 24th day of gestation to the 13th day after birth, shows a quick development of the structures of the caecal and colic mucosal layers to the adult forms, from the very first week of postnatal life. The distal part of the colon is full-grown before the other parts of the alimentary canal, and is particularly rich in mucous cells. The caecum is the place where an early lymphoid defense is provided, from the 30th day of gestation.

Prenatal and postnatal development of the small intestine in the insectivore Suncus murinus

The development of the small intestine in the insectivore Suncus murinus was noted during the period from 21 days' gestation to 20 days after birth. At 21 days of gestation, the proximal small intestine exhibited the beginning of villus formation, whereas the distal small intestine preserved the stratified epithelium. Stratified epithelium in the distal small intestine changed into a single layer by 24 days' gestation. At 26 days' gestation, each epithelial cell was immature; but by 28 days mature-looking epithelial cells were found. The shape of the villi changed from cuboid to columnar during the same period. The connective-tissue cores of the villi began to develop at 7 days after birth in the proximal small intestine and at 15 days after birth in the distal small intestine. Crypts appeared at 15 days after birth. Endocytosis of epithelial cells took place at 28 days of gestation. In the proximal small intestine, supranuclear vesicle clusters were observed first at birth; they began to decrease both in number and size at 10 days' gestation and then disappeared completely by 20 days after birth. In the distal small intestine, large supranuclear vacuoles were observed first at 28 days of gestation. Although these vacuoles invariably were found up to 15 days after birth, they also disappeared completely by 20 days. Epithelial cells showed a structure similar to those of the adult after weaning.

Postnatal development of transport function in the pig intestine

1. In the newborn pig it appears that only prenatally produced enterocytes are capable of absorbing large amounts of protein. 2. The ability of the small intestine to transport sodium, lysine, lysine containing dipeptides and glucose declines markedly during the first week of post natal life. 3. Dexamethosone causes a doubling of the sodium dependent portion of alanine uptake. 4. EGF given between days three and six of postnatal life increases sucrase and maltase activity in the distal region of the small intestine. 5. Weaning induced problems are probably not due to direct inhibition of transport properties.

"M" cell distribution in follicle-associated epithelium of mouse Peyer's patch

The distribution of "M" cells within the follicle-associated epithelium (FAE) of mouse Peyer's patches has been estimated from a series of SEM micrographs. "M" cells are found generally to be distributed evenly throughout the higher regions of the FAE. The frequency with which "M" cells occur decreases in the lower regions of the FAE. No "M" cells are found in the follicle-associated crypts. "M" cell microvilli are longer than those of enterocytes found at the base of the follicle-associated crypts and shorter than those found on enterocytes in other parts of the FAE. No lymphoid cells occur within the epithelium of the follicle-associated crypt. Lymphoid cells in the higher regions of the FAE are associated closely with "M" cells. There is, in the lower regions of the FAE, a transitional zone where lymphoid cells occur both free within the epithelium and closely associated with "M" cells. It is suggested that an initial close association of lymphoid cells with young, fully differentiated enterocytes is responsible for the latter's subsequent transformation to "M" cells.