Helicobacter pylori Adapts to Chronic Infection and Gastric Disease via pH-Responsive BabA-Mediated Adherence.

The BabA adhesin mediates high-affinity binding of Helicobacter pylori to the ABO blood group antigen-glycosylated gastric mucosa. Here we show that BabA is acid responsive-binding is reduced at low pH and restored by acid neutralization. Acid responsiveness differs among strains; often correlates with different intragastric regions and evolves during chronic infection and disease progression; and depends on pH sensor sequences in BabA and on pH reversible formation of high-affinity binding BabA multimers. We propose that BabA's extraordinary reversible acid responsiveness enables tight mucosal bacterial adherence while also allowing an effective escape from epithelial cells and mucus that are shed into the acidic bactericidal lumen and that bio-selection and changes in BabA binding properties through mutation and recombination with babA-related genes are selected by differences among individuals and by changes in gastric acidity over time. These processes generate diverse H. pylori subpopulations, in which BabA's adaptive evolution contributes to H. pylori persistence and overt gastric disease.

The genital econiche: focus on microbiota and bacterial vaginosis.

Ecological and evolutionary forces shaping the normal and abnormal microflora of the genital econiche are discussed, in particular those related to bacterial vaginosis, which worldwide is the most common vaginal infection, with numerous obstetrical and gynecological complications, including acquisition and transmission of HIV and other sexually transmitted infections (STIs). Characterized by a heavy overgrowth of Gram-negative and Gram-positive anaerobes with no signs of inflammation, bacterial vaginosis has been regarded a microbiological and immunological enigma. Immune tolerance to both normal and abnormal vaginal microbiota, mainly derived from gut microflora, as a result of coevolution with humans might explain the absence of inflammation, supported by short-chain fatty acids, known to modulate immune responses, that are produced in large quantities by anaerobes. Recent studies have implicated the development of a vaginal biofilm with Gardnerella vaginalis and Atopobium vaginae as main players in the pathogenesis of bacterial vaginosis. Supporting this conclusion are data such as those demonstrating heavy growth of G. vaginalis and diversified anaerobes with numerous "clue cells" that are sloughing off from the biofilm. Gardnerella and Atopobium organisms attached to these clue cells can be demonstrated in the male genital econiche, likely reflecting a heterosexual transmission of the disorder.

The possible role of transplacentally-acquired antibodies to infectious agents, with molecular mimicry to nervous system sialic acid epitopes, as causes of neuromental disorders: prevention and vaccine implications.

Proof of causality of most neuromental disorders (NMD's) is largely unavailable. Lessons from four-decade investigations of the epidemiology, immunology, pathogenesis, prevention and therapy of perinatal infectious agents, which invade directly the nervous system, have led us to propose a new indirect effect hypothesis: maternal transplacentally-acquired antibodies, to agents with epitope molecular mimicry with the developing nervous system, can cross the fetus/infant's blood-nervous system barriers to cause NMD's, clinically manifest years later. Further rationale is provided by relevant evolutionary/developmental (EVO-DEVO) considerations - applicable also to some vaccines. The hypothesis is being tested in: (a) older pregnancy studies with available maternal and newborn sera, and follow-up of the progeny for NMD's; and (b) NMD registry individuals linked to their stored newborn blood spots. Preliminary results support a possible role for schizophrenia of high-tittered antibodies to some agents (toxoplasma, influenza and herpes simplex type 2 virus). A model that includes likely genetic and postnatal influences is schematized and a list of putative agents and factors, based on varying rationales, is tabulated. In case pilot studies are confirmed, the identified agent(s) and antibodies would need to be tested in new prospectively enrolled pregnant women, so as to establish further risk factors leading to possible preventive modalities.

Helicobacter pylori adhesion to carbohydrates.

Adherence of bacterial pathogens to host tissues contributes to colonization and virulence and typically involves specific interactions between bacterial proteins called adhesins and cognate oligosaccharide (glycan) or protein motifs in the host that are used as receptors. A given pathogen may have multiple adhesins, each specific for a different set of receptors and, potentially, with different roles in infection and disease. This chapter provides strategies for identifying and analyzing host glycan receptors and the bacterial adhesins that exploit them as receptors, with particular reference to adherence of the gastric pathogen Helicobacter pylori.

Genotypic and phenotypic stability of Helicobacter pylori markers in a nine-year follow-up study of patients with noneradicated infection.

The cagA gene, alleles of the vacA gene,random amplified polymorphic DNA (RAPD), and neutrophil activating capacity (HpNAC) were used to examine paired H. pylori isolates from 10 noneradicated individuals 9 years apart. Paired isolates from each patient were indistinguishable with regard to vacA alleles, RAPD, and HpNAC. Isolates from nine patients showed concordance for the cagA gene, which was not detected in the recent isolate of the tenth patient. Antibodies to CagA were, however, demonstrated in the serum specimens 9 years apart and were also present in two other patients whose paired isolates were cagA-, indicating the existence of both cagA+ and cagA-organisms, with the latter predominating in some patients. The present study suggests a greater stability of phenotypic and genotypic markers of H. pylori than previously regarded. This might be true for a community with low infection and transmission rates. Complementary techniques like microarrays might, however, disclose evolutionary changes not identified here.

The sialic acid binding SabA adhesin of Helicobacter pylori is essential for nonopsonic activation of human neutrophils.

Infiltration of neutrophils and monocytes into the gastric mucosa is a hallmark of chronic gastritis caused by Helicobacter pylori. Certain H. pylori strains nonopsonized stimulate neutrophils to production of reactive oxygen species causing oxidative damage of the gastric epithelium. Here, the contribution of some H. pylori virulence factors, the blood group antigen-binding adhesin BabA, the sialic acid-binding adhesin SabA, the neutrophil-activating protein HP-NAP, and the vacuolating cytotoxin VacA, to the activation of human neutrophils in terms of adherence, phagocytosis, and oxidative burst was investigated. Neutrophils were challenged with wild type bacteria and isogenic mutants lacking BabA, SabA, HP-NAP, or VacA. Mutant and wild type strains lacking SabA had no neutrophil-activating capacity, demonstrating that binding of H. pylori to sialylated neutrophil receptors plays a pivotal initial role in the adherence and phagocytosis of the bacteria and the induction of the oxidative burst. The link between receptor binding and oxidative burst involves a G-protein-linked signaling pathway and downstream activation of phosphatidylinositol 3-kinase as shown by experiments using signal transduction inhibitors. Collectively our data suggest that the sialic acid-binding SabA adhesin is a prerequisite for the nonopsonic activation of human neutrophils and, thus, is a virulence factor important for the pathogenesis of H. pylori infection.

Helicobacter pylori prevalence among indigenous peoples of South America.

The seroprevalence of Helicobacter pylori among secluded Indian populations of South America was determined to gain insight into the evolutionary history and possible transmission patterns of the organism. Serum samples obtained from 1024 donors in 22 different villages were tested by enzyme-linked immunosorbent assay for immunoglobulin G antibodies, and the results were confirmed by Western blot. The overall seroprevalence was 92%: >80% of children tested positive by 3 years of age, the highest prevalence in populations studied to date. Comparison of H. pylori prevalence with that of herpes simplex virus type 1, which is known to be transmitted orally, demonstrated a linear correlation in their prevalence rates, suggesting that these pathogens share risk factors. However, H. pylori seroprevalence was consistently higher, indicating that additional routes of transmission exist and/or that the organism is more transmissible. Seroprevalence did not correlate with the length of contact with the outside world. These results suggest that H. pylori was indigenous to the South American Indians and was not introduced by contact with outsiders.

Lactotetraosylceramide, a novel glycosphingolipid receptor for Helicobacter pylori, present in human gastric epithelium.

The binding of Helicobacter pylori to glycosphingolipids was examined by binding of (35)S-labeled bacteria to glycosphingolipids on thin-layer chromatograms. In addition to previously reported binding specificities, a selective binding to a non-acid tetraglycosylceramide of human meconium was found. This H. pylori binding glycosphingolipid was isolated and, on the basis of mass spectrometry, proton NMR spectroscopy, and degradation studies, were identified as Galbeta3GlcNAcbeta3Galbeta4Glcbeta1Cer (lactotetraosylceramide). When using non-acid glycosphingolipid preparations from human gastric epithelial cells, an identical binding of H. pylori to the tetraglycosylceramide interval was obtained in one of seven samples. Evidence for the presence of lactotetraosylceramide in the binding-active interval was obtained by proton NMR spectroscopy of intact glycosphingolipids and by gas chromatography-electron ionization mass spectrometry of permethylated tetrasaccharides obtained by ceramide glycanase hydrolysis. The lactotetraosylceramide binding property was detected in 65 of 74 H. pylori isolates (88%). Binding of H. pylori to lactotetraosylceramide on thin-layer chromatograms was inhibited by preincubation with lactotetraose but not with lactose. Removal of the terminal galactose of lactotetraosylceramide by galactosidase hydrolysis abolished the binding as did hydrazinolysis of the acetamido group of the N-acetylglucosamine. Therefore, Galbeta3GlcNAc is an essential part of the binding epitope.

Production of tumor necrosis factor-alpha and interleukin-6 in whole blood stimulated by live Gram-negative and Gram-positive bacteria.

OBJECTIVE: To investigate the production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) induced by live Gram-negative and Gram-positive bacteria in whole blood in vitro. METHODS: In all, 49 different isolates were studied. Each of the 49 different isolates was incubated for 4 h with whole blood at a ratio of one monocyte per 1--5 bacteria. Plasma was then separated and frozen, and the concentrations of TNF-alpha and IL-6 were measured by enzyme immunoassays. RESULTS: There was a positive correlation between TNF-alpha and IL-6 values, r=0.9. Gram-negative bacteria induced higher levels of both TNF-alpha and IL-6 than Gram-positive bacteria. Group G streptococci (GGS) induced higher levels of TNF-alpha than Streptococcus pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis and group A streptococci (GAS). Klebsiella pneumoniae induced higher levels of TNF-alpha than Haemophilus influenzae, Escherichia coli and Neisseria meningitidis. GGS induced higher levels of IL-6 than Staphylococcus epidermidis, Staphylococcus aureus and GAS. When the relative amounts of cytokine induced by the strains were compared to serum concentrations measured on admission in patients with bacteremia caused by the same bacterial isolates there was no significant correlation. CONCLUSION: Species- and strain-related differences in cytokine-inducing properties were found which may have significance in clinical infections.

Granulocyte colony-stimulating factor (G-CSF) and interleukin (IL)-8 in sera from patients with Staphylococcus aureus septicemia.

OBJECTIVE: To determine the concentrations of granulocyte colony-stimulating factor (G-CSF) and interleukin (IL)-8 in sera from patients with Staphylococcus aureus septicemia and to correlate the results to peripheral neutrophil counts and the clinical outcome. METHODS: Serum samples from 64 consecutive patients with S. aureus septicemia were sequentially collected in a prospective study. RESULTS: The mean plus minus standard deviation (SD) serum G-CSF value on admission was 348 plus minus 830 with a range of 8 to 5400 pg/mL. G-CSF concentrations were elevated (> 76 pg/mL) in 38/64 patients (59%) as were serum IL-8 concentrations (> 67 pg/mL) in 23/64 patients (36%) on admission. The mean plus minus SD IL-8 value was 266 plus minus 422 pg/mL with a range of 2 to 1366 pg/mL. A correlation was found between serum IL-8 and white blood cell count on admission (p=0.008). CONCLUSIONS: Patients with uncomplicated septicemia frequently have elevated G-CSF values (84%) in comparison to patients with complicated septicemia (49%; p=0.02), indicating a possible protective effect of G-CSF in septic complications.