BSCI 424 — PATHOGENIC MICROBIOLOGY — Fall 2000

Helicobacter Summary

Taxonomy:

  Helicobacter was first observed in 1983 as Campylobacter-like organisms (formerly Campylobacter pyloridis) in the stomachs of patients with type B gastritis

  Nomenclature Helicobacter was first established in 1989

 Campylobacter, Helicobacter, Wolinella, Arcobacter and Flexispira belong to a single phylogenetic group that is distinct from other Gram-negative bacteria and based on 16S rRNA sequencing, DNA hybridization, genus-specific probes, cell wall protein and lipid characterization, serological and biochemical analyses

 Campylobacter and Helicobacter (formerly Campylobacter) are the most clinically important members of the rRNA superfamily

 Recently defined family Campylobacteriaceae contains the genera Campylobacter and Arcobacter

 Helicobacter, Wolinella, and Flexispira now included in a phylogenetically distinct family, as yet unnamed

 Helicobacter (17 species by rRNA sequencing)

 Human Pathogens: only three species are currently considered to be human pathogens

  Helicobacter pylori

 

  H. cinaedi and H. fennelliae: formerly called Campylobacter-like organisms (CLOs)

 Many other species: some are minor pathogens

Morphology & Physiology:

General Characteristics Common to Superfamily:

 Pleomorphic helical (spiral or curved) Gram-negative microaerophilic organisms (see WebLinked Helicobacter image)

 Characteristics that facilitate penetration and colonization of mucosal environments (e.g., Motile by polar flagella; corkscrew shape)

 Become coccoid when exposed to oxygen or upon prolonged culture

 Neither ferment nor oxidize carbohydrates; Low DNA G+C base ratio

Helicobacters:

  Cells have blunted/rounded ends in gastric biopsy specimens; On agar medium cells become rod-like and coccoid on prolonged culture

  Abundant quatities of urease produced only by gastric strains

  Abundant quatities of mucinase produced

  Abundant quatities of catalase produced

  H. pylori are highly motile by lophotrichous flagella (tufts of flagella at poles of cell)

  Smooth cell wall with unusual fatty acids

  H. fennellae and H. cinaedi have a single polar flagellum

Clinical Syndromes:

  Helicobacter pylori is major human pathogen

  Gastritis (acute or chronic) (see WebLinked image); chronic superficial gastritis: associated with gastric antral epithelium in patients with active chronic gastritis

  Peptic (gastric) (see WebLinked image) and duodenal ulcers  

  Associated with gastric adenocarcinoma (stomach cancer) (see WebLinked image)

  Other Helicobacters: H. cinaedi and H. fennelliae (formerly called Campylobacter-like organisms (CLOs)): homosexual men

  Proctitis

  Proctocolitis 

  Enteritis 

  Bacteremia

Epidemiology:

Helicobacter pylori:

  No animal resevervoir; only found in humans

  Colonize stomach and duodenum of man and many animal species

  Colonize mucosal lining of stomach

  Mucosa protects the stomach wall from gastric digestive enzymes and hydrochloric acid and provides protective niche for helicobacters from immune response

  Family Clusters; Believed to be orally transmitted person-to-person

  Developed Countries:

  United States: 30% of total population infected

  Of that 30%, about 1% per year develop duodenal ulcer; Approximately one third eventually have peptic ulcer disease(PUD)

  70% of persons with gastric ulcers are colonized with H. pylori

 Nearly all persons with duodenal ulcer are colonized

  Most gastric adenocarcinomas and lymphomas are concurrent with or preceded by an infection with H. pylori

  Worldwide, H. pylori affects about 20% of persons below the age of 40 years, and 50% of those above the age of 60 years; H. pylori is uncommon in young children.

  Low socioeconomic status correlates with H. pylori infection

  Developing Countries:

  Most adults infected

  About 10% acquisition rate per year for children between 2 and 8 years of age

H. cinaedi and H. fennelliae:

  Isolated from male homosexuals; rodents

  Colonize human intestinal tract and cause disease

  Often transmitted through sexual practices

Pathogenesis & Immunity:

  Cellular components:

  Colonization: Adherent to gastric surface epithelium or pit epithelial cells deep within the mucosal crypts adjacent to gastric mucosal cells

  Multiple polar, sheathed flagella: highly motile; corkscrew motility enables penetration into viscous environment (mucus)

  Adhesins: hemagglutinins; sialic acid binding adhesin; Lewis blood group adhesin

   Extracellular components:

   Mucinase: degrades gastric mucus; localized tissue damage

  Acid-inhibitory protein  

  Bacterial urease converts urea (abundant in saliva and gastric juices) into bicarbonate (to CO₂) and ammonia, strong bases that neutralize the local acid environment; Localized tissue damage

  Tissue damage:

  Vacuolating cytotoxin: epithelial cell damage

  Produce great deal of ammonium ion and CO₂ with localized tissue damage  

  Invasin(s)(??): Poorly defined (e.g., hemolysins; phospholipases; alcohol dehydrogenase)

  Protection from phagocytosis and intracellular killing:

   Superoxide dismutase

 Catalase

  Immune Response: Immunopathogenesis

  Mucus protects H. pylori from body's natural defenses

  Vacuolating cytotoxin, urease, and LPS stimulate inflammatory response  

  Chronic inflammation with leukocytes, killer T cells, and other inflammatory responders

  PMNs die and lyse, releasing destructive compounds (e.g., superoxide radicals) on stomach lining cells  

 Humoral immune response antibody titers persist for years

Laboratory Identification:

  Helicobacters can be recovered from or detected in endoscopic antral gastric biopsy material; Multiple biopsies should be taken

  Characteristically shaped organisms can be seen at high magnification with silver-stained (see WebLinked image), hematoxylin and eosin (H & E) stained (see WebLinked image) or methylene blue stained (see WebLinked image) biopsy specimens of gastric antrum (antral biopsies) in the mucosa adherent to the surface epithelium or pit epithelial cells deep within the crypts; Always found adjacent to gastric mucosal cells

  Transport media for culture: nutrient, thioglycollate, Brucella, brain-heart infusion, supplemented tryptic soy broths and semi-solid agars (e.g., Wang’s blood-supplemented medium) have all been used for transport

  Culture: insensitive

Complex basal media (agar or broth) supplemented with whole blood, heme, serum, charcoal, cornstarch, or egg yolk emulsion

Grow optimally under microaerobic conditions (C rich atmosphere for broth culture)

  Identification:

  Histology and/or culture isolation; characterization by: 16S rRNA sequencing; fatty acid composition; presence of multiple, sheathed flagella; biochemical tests

  Urease test (endoscopic or breath): can detect alkaline by-products  

  Species differentiated by SDS-PAGE, serology, and aryl sulfatase activity

  Antibody detection: since antibody titers persist for years, cannot differentiate between past and present infections; useful to document exposure

Treatment, Prevention & Control:

  Triple Chemotherapy (synergism)

  Proton pump inhibitor (e.g., omeprazole = Prilosec^(R))

  One or more antibiotics (e.g., clarithromycin; amoxicillin; metronidazole): in vitro susceptibility to erythromycin, rifampin, tetracycline, and metronidazole; Resistance to nalidixic acid and sulfonamides  

  Bismuth compound: sensitivity to bismuth salts

  FDA Advisory Committee Recommends Dual Therapy

Prilosec^(R) (omeprazole); 40mg q.d.

Biaxin^(R) (clarithromycin); 500mg t.i.d

  Inadequate Treatment Can Result in Recurrence of Symptoms

 

 

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