Helicobacter Pylori

who discovered H. pylori

J.R. Warren (born 11 June 1937 in Adelaide) is an Australian pathologist, Nobel Laureate and researcher who is credited with the 1979 re-discovery of the bacterium Helicobacter pylori, together with Barry Marshall.[1] The duo proved to the medical community that the bacterium Helicobacter pylori (H. pylori)[1] is the cause of most peptic ulcers.

What is the defining feature of H. pylori? How does it cope?

It colonizes the stomach in an area that was once thought inhospitable because of low pH To cope, it burrows deep into the mucus layer at the surface of the epithelia where pH is maintained at 7 by the gradient from the mucus

diagnosis of H. pylori

#1 = breath test (highly accurate, active infection); blood test (antigen exposure), endoscopy (invasive)

function of VacA

-disrupts cell polarity -promotes apoptosis of epithelial cells -inhibits T cell proliferation and effector functions

Describe H. pylori LPS structure and function (3)

1. 4 acyl groups on Lipid A instead of 6, and dephosphorylation of Lipid A 2. Lipid A is 1000X less immunogenic because of these modifications, therefore contributes to H. pylori's chronic evasive nature 3. O-Ag of LPS also mimics Lewis Blood Ags, therefore shielding H. pylori by using peripheral tolerance

Describe CagA transport (2)

1. CagL tip of the T4SS binds a5b1 integrin via an RGD sequence, triggering its insertion in to the membrane and allowing it to inject CagA 2. Binding to a5b1 also triggers downstream activation of Src kinases which will later help (P) EPIYA of CagA

Describe H. pylori's clinical significance (3)

1. Causes gastritis (inflammation of stomach lining) 2. Gastric ulcers (defective/damaged epithelia) 3. Gastric cancer (lymphoma = cancer of GALT, or adenocarcinoma = cancer of epithelia)

How do CagA polymorphisms affect its function (2)

1. EPIYA-C binds 1 SH2 domain of SHP2. Because SHP2 has two SH2 domains, therefore variants that have greater than 1 EPIYA-C will better bind and activate SHP2. Therefore, these variants have a higher virulence 2. EPIYA-D binds SH2's better than EPIYA-C, therefore, the eastern strain seems more virulent in general than the western strain

Describe the cag pathogenicity island structure, polymorphism, and incidence (3)

1. Encode a T4SS and the effector, CagA 2. Major polymorphisms of the CagA gene at regions that encode the CagA EPIYA (P) motifs, thus the polymorphisms are called EPIYA A-D 3. Western H. pylori strains have CagA encoding EPIYA A and 1-6 EPIYA C motifs. Eastern strains encode A with D's instead of C's

Describe the history of H. pylori (3)

1. First isolated in 1983 2. Called campylobacter because of its curved shape 3.. 1989: identified as a new species with 16S rRNA seq

Describe H. pylori's epidemiology. How is it spread? (2)

1. Found in 50% of world's population as an asymptomatic chronic infection 2. Mode of transmission is oral, mainly from parents' saliva to children

Describe H. pylori adhesins and their target (2)

1. Has 3 afimbrial adhesins that are autotransporters (BabA, SabA, OipA) 2. Bind lewis group Ags

Describe the function of CagA effector (4)

1. Has a K/R-rich motif that upon entry into the cytosol binds +charged phosphatidylserine residues on the membrane inner leaflet 2. (P) by host tyrosine kinases (Src kinases) at the Y of EPIYA motifs 3. (P) EPIYA recruits host phosphatase SHP-2 4. SHP-2 de(P) ERK, which will active the cell cycle to promote dysregulated cell proliferation. Therefore, depending on which host cell has been injected, this may cause adenocarcinomas or lymphomas

What is HopQ (2)?

1. Helps with T4SS-mediated injection by being a co-receptor to host CAECAM5 which tightens the adhesion 2. Can explain why H. pylori does not colonize the top of the stomach (low CAECAM5) but does the bottom (high CAECAM5)

Describe VacA, transport, structure and classical function (7)

1. Is a secreted autotransporter pro-exotoxin 2.Sec-mediated transport to periplasm where its C-terminus inserts into the OM as a beta barrel, moving the passenger domain outside. A surface peptidase will cleave the passenger domain as the mature exotoxin 3. Mature toxin has p33 and p55 subunits. The mature toxin polymerizes into a dodecamer that can insert into the host membrane 4. Induces endocytosis and in the vesicle is a Cl- import channel 5. Endosomal ATPases will import protons to balance the ionic imbalance, decreasing vesicular pH 6. Membrane-permeant weak bases passively diffuse into the acidic vesicle and are irreversibly protonated 7. Vesicles swell from these acid-base salts, causing osmotic swelling and eventually cell death

What are major virulence factors encoded by H. pylori (6)?

1. Motility and adhesion = 2 flagellin proteins and 4 chemoreceptors 2. Adhesins = afimbrial adhesins called autotransporters (therefore is a T5SS) 3. Urease 4. LPS endotoxin 5. VacA exotoxin (also a T5SS autotransporter) 6. cagA encoding a T4SS and its effector toxin, CagA

What is VacA's immunomodulatory effect (2)?

1. VacA monomers (which have the two subunits) bind LFA-1, inducing internalization. Cytosolic VacA blocks calcineurinA de(P) of NFAT, which blocks its translocation. No NFAT = no transcription of IL-2, blocking T cell proliferation 2. VacA with GGT will block T cell responses by promoting tolerogenic DCs, which in turn skew T cell differentiation to the Treg lineage

Define the structure and modifications of H. pylori flagella. What is the chemotaxis system? (3)

1. flagella composed of two subunits (FlaA major and FlaB tip) glycosylated to provide extra stability 2. Its glycosylation (and structure generally) also reduces immunogenicity contributing to immune evasion 2. 4 chemoreceptors (TlpA-D) that sense attractants (urea, bicarbonate, arginine) 3. e.g. TlpA binds arginine and bicarbonate and TlpB senses pH and the QS signal AI-2

Describe the general characteristics of H. pylori (6)

1. gram- 2. motile (flagella-mediated) 3. curved bacilli 4. microaerophilic (needs O2 at subatmospheric concentrations 5. urease-producing 6. classified as an extracellular pathogen

how many people get duodenal ulcers; how many get gastric carcinoma

10-15% 1%

What is required for urease function (2)? What is unique about one?

2 transporters 1. To insert the nickel (a nickel-ion transporter) 2. A urea transporter called Ure1. Ure1 is pH sensitive, and only activates when pH drops below 6.5 (thus the pH shield is only formed when required)

How is H. pylori treated?

A tri-cocktail of two antibiotics (clarithryomycin and metronidazole) and a proton pump inhibitor

What is urease?

Cytosolic Ni2+ enzyme hydrolyses urea to basic ammonia and CO2. The basic ammonia forms a pH shield in the periplasm that protects the bacteria from the low pH if it's in the stomach lumen (like during transfer to a new host)

what is H. pylori resistant to

DNA damaging molecules like superoxide dismutase, catalase, and arginase

H. pylori expresses ____ and lacks the classic ___ response

DNA repair proteins (RecA); SOS response

___ helps pathogenic bacteria survive

Fe 2+ (iron)

characteristics of H. pylori

Helicobacter pylori (H. pylori) is a spiral-shaped bacterium that is found in the gastric mucous layer or adherent to the epithelial lining of the stomach. H. pylori causes more than 90% of duodenal ulcers and up to 80% of gastric ulcers. , motile, gram negative rod, can be cultured in 37 degrees Celsius

colonizes ___% of human population

Helicobacter pylori is a spiral-shaped Gram-negative bacterium that colonizes the stomach in about 50% of all humans. In countries with high socio-economic standards infection is considerably less common than in developing countries where virtually everyone may be infected.

How does H. pylori peptidoglycan affect host immunity?

Peptidoglycan is injected into the cytosol by T4SS where it is recognized by NLR1, and with unidentified ligands this activates NLRP3 inflammasome to produce IL-1beta and IL-18

Describe vacA polymorphisms (2)

There are a lot of variants of the vacA gene 1. Two major variants each of the signal sequence (for sec-mediated transport) and passenger domain: S1/2 and M1/2 2. S1M1 is most virulent VacA; S1M2 is more moderate; no S2 variants are pathogenic

H. pylori toxins

VacA and CagA

How common is H. pylori-associated stomach cancer? Why (2)?

While enough to be classified a grade 1 carcinogen, still rare: 1. host polymorphisms provide production 2. Significant genetic diversity in the species means that most don't have the required genes encoding virulence factors (vacA and the cag pathogenicity island)

symptoms of H. pylori

ache or burning pain in abdomen abdominal pain worse than when stomach is empty nausea, loss of appetite frequent burping, bloating, and weight loss

most people with H. pylori infection are

asymptomatic

H. pylori has _____ in response to DNA damage

competence up-regulated

increase in H. pylori colonization correlates with ____

decrease in Crohn's disease, allergic asthma, and ulcerative colitis

where can H. pylori be found other than stomach

dental plaque, houseflies, human and animal feces, and natural waters

steps for treating H. pylori

diagnosis (breath test) --> treatment (antibiotics) --> re-test (breath test, not blood test) --> retreat if necessary

what does H.pylori cause

duodenal and stomach ulcers; associated with gastric cancers

define CagA (cytotoxin-associated gene A)

encoded by the cag pathogenicity island

what helps H. pylori colonize

flagella, chemotaxis, urease, and helical shape

where does H. pylori colonize

from stomach lumen to mucous layer

is H. pylori responsive to antibiotic therapy?

highly responsive

what causes H. pylori to be in a viable but non-culturable (VBNC) state

morphing from rod-shaped to coccoid form (when stressed)

define VacA (vacuolating cytotoxin)

pore-forming toxin

function of CagA

promotes inflammation; interacts with host cell signaling pathways--> altered cell polarity + proliferation --> bacterial nutrient and iron acquisition; increases cancer risk (bacterial oncoprotein)

____ on cell surface help shift balance for H. pylori (and give the examples)

proteins; BabA and SabA

describe breath test

radioactively label enzyme with urea; collect breath in a balloon and transfer to a vial to count

define chemotaxis

senses low pH and moves organism to high pH

how many bacterial species in H. pylori

up to 200