Bacterial epithelial cell cross talk

Interactions between host and oral commensal microorganisms are key events in health and disease status

The oral cavity has sometimes been described as a mirror that reflects a person's health. Systemic disease such as diabetes or vitamin deficiency may be seen as alterations in the oral mucosa. A variety of external factors cause changes in the oral mucosa, thus altering mucosal structure and function, and promoting oral pathologies (most frequently bacterial, fungal and viral infections). Little is known, however, about immune surveillance mechanisms that involve the oral mucosa.There is no direct contact between specific immune cells in the basal epithelium and microorganisms in the upper layers of the oral mucosa. The author's hypothesis is that the protective immunity is conveyed through epithelial cells. The present brief review assesses the oral mucosa's role as the main defense in the interactions between the host and the oral microbial community. A unique model was used to investigate these interactions as the cause of oral disease and to develop new treatments that exploit our knowledge of the host-microorganism relationship.

Positive correlation between low adhesion of group A Streptococcus to mammalian cells and virulence in a mouse model

We previously reported that a mouse model reflected, at least in part, the pathogenic mechanism of bacteremia observed during streptococcal toxic shock syndrome caused by group A Streptococcus (GAS). We have extended this study by assaying the in vitro adhesion of these same isolates to mammalian cells. Unexpectedly, we found that high-virulence GAS isolates in the mouse model showed low adhesion to the host cells. Similarly, the rate of recovery from the peritoneal cavity and cardiac blood of mice after intraperitonial injection was higher for high- than for low-virulence strains. Levels of expression of molecules that affect the adhesion of GAS to host cells were not significantly correlated with GAS virulence. Taken together, these results indicate that the invasiveness of GAS, reflected as higher virulence, is correlated directly with lower adhesion to host cells.

Probiotic bacteria change Escherichia coli-induced gene expression in cultured colonocytes: Implications in intestinal pathophysiology

AIM: To investigate the change in eukaryotic gene expression profile in Caco-2 cells after infection with strains of Escherichia coli and commensal probiotic bacteria.

METHODS: A 19200 gene/expressed sequence tag gene chip was used to examine expression of genes after infection of Caco-2 cells with strains of normal flora E. coli, Lactobacillus plantarum, and a combination of the two.

RESULTS: The cDNA microarray revealed up-regulation of 155 and down-regulation of 177 genes by E. coli. L. plantarum up-regulated 45 and down-regulated 36 genes. During mixed infection, 27 genes were up-regulated and 59 were down-regulated, with nullification of stimulatory/inhibitory effects on most of the genes. Expression of several new genes was noted in this group.

CONCLUSION: The commensal bacterial strains used in this study induced the expression of a large number of genes in colonocyte-like cultured cells and changed the expression of several genes involved in important cellular processes such as regulation of transcription, protein biosynthesis, metabolism, cell adhesion, ubiquitination, and apoptosis. Such changes induced by the presence of probiotic bacteria may shape the physiologic and pathologic responses they trigger in the host.

Intestinal M cells: The fallible sentinels?

The gastrointestinal tract represents the largest mucosal membrane surface in the human body. The immune system in the gut is the first line of host defense against mucosal microbial pathogens and it plays a crucial role in maintaining mucosal homeostasis. Membranous or microfold cells, commonly referred to as microfold cells, are specialized epithelial cells of the gut-associated lymphoid tissues (GALT) and they play a sentinel role for the intestinal immune system by delivering luminal antigens through the follicle-associated epithelium to the underlying immune cells. M cells sample and uptake antigens at their apical membrane, encase them in vesicles to transport them to the basolateral membrane of M cells, and from there deliver antigens to the nearby lymphocytes. On the flip side, some intestinal pathogens exploit M cells as their portal of entry to invade the host and cause infections. In this article, we briefly review our current knowledge on the morphology, development, and function of M cells, with an emphasis on their dual role in the pathogenesis of gut infection and in the development of host mucosal immunity.

Competitive inhibition of adherence of enterotoxigenic Escherichia coli, enteropathogenic Escherichia coli and Clostridium difficile to intestinal epithelial cell line Lovo by purified adhesin of Bifidobacterium adolescentis 1027

AIM: To observe competitive inhibition of adherence of enterotoxigenic Escherichia coli (ETEC), enteropathogenic Escherichia coli (EPEC) and Clostridium difficile (C. difficile) to intestinal epithelial cell line Lovo by purified adhesin of Bifidobacterium adolescentis 1027 (B. ado 1027).

METHODS: The binding of bacteria to intestinal epithelial cell line Lovo was counted by adhesion assay. The inhibition of adherence of ETEC, EPEC and C. difficile to intestinal epithelial cell line Lovo by purified adhesin of B. ado 1027 was evaluated quantitatively by flow cytometry.

RESULTS: The purified adhesin at the concentration of 10 µg/mL, 20 µg/mL and 30 µg/mL except at 1 µg/mL and 5 µg/mL could inhibit significantly the adhesion of ETEC, EPEC and C. difficile to intestinal epithelial cell line Lovo. Moreover, we observed that a reduction in bacterial adhesion was occurred with increase in the concentration of adhesin, and MFI (Mean fluorescent intensity) was decreased with increase in the concentration of adhesin.

CONCLUSION: The purified adhesin of B. ado 1027 can inhibit the adhesion of ETEC, EPEC and C. difficile to intestinal epithelial cell line Lovo in a dose-dependent manner.

Transcytosis: crossing cellular barriers

Transcytosis, the vesicular transport of macromolecules from one side of a cell to the other, is a strategy used by multicellular organisms to selectively move material between two environments without altering the unique compositions of those environments. In this review, we summarize our knowledge of the different cell types using transcytosis in vivo, the variety of cargo moved, and the diverse pathways for delivering that cargo. We evaluate in vitro models that are currently being used to study transcytosis. Caveolae-mediated transcytosis by endothelial cells that line the microvasculature and carry circulating plasma proteins to the interstitium is explained in more detail, as is clathrin-mediated transcytosis of IgA by epithelial cells of the digestive tract. The molecular basis of vesicle traffic is discussed, with emphasis on the gaps and uncertainties in our understanding of the molecules and mechanisms that regulate transcytosis. In our view there is still much to be learned about this fundamental process.

Characterization of a cytotoxic factor in culture filtrates of Serratia marcescens

Serratia marcescens culture filtrates have been reported to be cytotoxic to mammalian cells. Using biochemical and genetic approaches, we have identified a major source of this cytotoxic activity. Both heat and protease treatments abrogated the cytotoxicity of S. marcescens culture filtrates towards HeLa cells, suggesting the involvement of one or more protein factors. A screen for in vitro cytotoxic activity revealed that S. marcescens mutant strains that are deficient in production of a 56-kDa metalloprotease are significantly less cytotoxic to mammalian cells. Cytotoxicity was significantly reduced when culture filtrates prepared from wild-type strains were pretreated with either EDTA or 1,10-phenanthroline, which are potent inhibitors of the 56-kDa metalloprotease. Furthermore, cytotoxic activity was restored when the same culture filtrates were incubated with zinc divalent cations, which are essential for enzymatic activity of the 56-kDa metalloprotease. Finally, recombinant expression of the S. marcescens 56-kDa metalloprotease conferred a cytotoxic phenotype on the culture filtrates of a nonpathogenic Escherichia coli strain. Collectively, these data suggest that the 56-kDa metalloprotease contributes significantly to the in vitro cytotoxic activity commonly observed in S. marcescens culture filtrates.

Bladder calculi in augmentation cystoplasty in children

OBJECTIVES

To determine the best preventive strategies for bladder calculi in children with an augmented bladder, the risk factors and prevention strategies for urolithiasis were evaluated.

METHODS

The records of 89 patients following augmentation cystoplasty were reviewed to assess the results of augmentation cystoplasties and in particular the formation and prevention of calculi.

RESULTS

The median follow-up was 4.9 years after augmentation. Most patients (71) had an ileocystoplasty. Bladder calculi occurred in 14 of the 89 patients (16%) and recurred in 4 patients. Girls had a higher incidence of urolithiasis. Other risk factors were cloacal malformations, vaginal reconstructions, anal atresia, clean intermittent catheterization problems and retention, bladder neck surgery, and symptomatic urinary tract infections.

CONCLUSIONS

Subgroups with cloacal malformations, vaginal reconstructions, ureter reimplantation, and bladder neck surgery were identified that have an increased risk for stone formation and therefore warrant special care in the follow-up after augmentation. This care should include clear emphasis on the role of treating symptomatic urinary tract infections, especially in patients with cloacal malformations and vaginal reconstructions. Girls have a higher incidence of bladder calculi than boys.

DNA adenine methylase mutants of Salmonella typhimurium show defects in protein secretion, cell invasion, and M cell cytotoxicity

Mutants of Salmonella typhimurium lacking DNA adenine methylase are attenuated for virulence in BALB/c mice. LD(50) values of a DNA adenine methylation (Dam)(-) mutant are at least 10(3)- to 10(4)-fold higher than those of the parental strain when administrated by oral or intraperitoneal routes. Dam(-) mutants are unable to proliferate in target organs but persist in low numbers in these locations. Efficient protection to challenge with the virulent parental strain is observed in mice infected with a Dam(-) mutant. Use of the ileal loop assay shows that Dam(-) mutants are less cytotoxic to M cells and fail to invade enterocytes. In the tissue culture model, lack of DNA adenine methylation causes reduced ability to invade nonphagocytic cells. In contrast, no effect is observed either in intracellular proliferation within nonphagocytic cells or in survival within macrophages. The invasion defect of Dam(-) mutants is correlated with a distinct pattern of secreted proteins, which is observed in both PhoP(+) and PhoP(-) backgrounds. Altogether, our observations suggest a multifactorial role of Dam methylation in Salmonella virulence.