Gastritis and Viral Gastroenteritis Flashcards
Mention important properties of Helicobacter pylori
- Gram-negative rods with comma, S-shaped or spiral-shaped
- Multiple flagella at one pole & motile
- Microaerophile
- Oxidase, catalase & urease positive
How is Helicobacter pylori transmitted?
- Natural habitat :
- human stomach & probably acquired by ingestion
- Person to- person transmission
- clustering of infection within families
Pathogenesis of Helicobacter pylori
- It attaches to mucus-secreting cells of gastric mucosa
- Production of large amounts of ammonia from urea by organism’s urease, coupled with inflammatory response ———> damage to mucosa
- Loss of protective mucus coating —> gastritis & peptic ulcer
- Ammonia neutralizes stomach acid, allowing organism to survive
Clinical findings of Helicobacter pylori
- Gastritis & peptic ulcer with recurrent pain in upper abdomen + frequently accompanied by bleeding into gastrointestinal tract
- stimulate B-cell proliferation & B-cell lymphoma—-> Antibiotic treatment directed against organism often causes tumor to regress
- No bacteremia or disseminated disease
How B-cell proliferation & B-cell lymphoma is formed in Helicobacter pylori?
H. pylori found in gastric mucosa-associated lymphoid tissue (MALT) lymphomas as chronic inflammation induced by organism ——-> stimulate B-cell proliferation & B-cell lymphoma
Diagnosis of H. pylori by non invasive method
Non invasive methods:
- Urea breath test:
* Radiolabeled urea is ingested.
* If organism is present ——> urease cleave ingested urea —-> radiolabeled CO 2 ——> radioactivity detected in breath - H. pylori stool antigen test:
* by enzyme-linked immunosorbent Assays
for initial diagnosis or confirmation of eradication - Serum IgG antibodies against H. pylori:
* Positive result indicates exposure to H. pylori
* but can not distinguish between past & current infection
* Antibodies may still be detected after eradication
Invasive methods (require biopsies) to diagnose H.pylori
- Gram-stained smears of biopsy specimens of gastric mucosa
- Rapid urease test
- Histological examination (Gold standard)
- Immunohistological staining
- Culture
- PCR of biopsy samples
How Rapid urease test for H.pylori is done?
- Gastric biopsy placed onto —-> urea containing medium with color indicator
- If H. pylori is present —> urease rapidly splits urea ( 1-2 hrs) —-> ammonia —-> shift in ph —-> color change
Which stains are used in Histological examination of H.pylori ?
- Hematoxylin
- eosin
- modified Giemsa stain or Warthin-Starry silver stain
How H.pylori looks like after a gastric biopsy in the gold standard test ?
slender, curved bacilli
Why is Immunohistological staining performed?
performed to improve sensitivity & specificity of detection
Which antibodies are stained during Immunohistological staining test ?
Monoclonal & polyclonal antibodies
H. pylori requires complex media for growth ; which media/s are used in its culture ?
- Non selective media :
* Chocolate, brain heart infusion & brucella agars
* supplemented with horse or rabbit blood - Selective media :
* Thayer-Martin agar, Pylori agar &
Dent’s medium
When culture for H.pylori is performed?
Culture is performed when patients are not responding to treatment & susceptibility to antibiotics is needed
When colonies appear & how they look like ?
When :
- Colonies appear in 2 to 5 days*at 37°C
- with low levels of oxygen (5 -10%) & increased levels of carbon dioxide (5 -12%)
Appearance:
* small (1 to 2 mm in diameter), translucent & nonhemolytic
Which test for H.pylori is limited due to accessibility & cost?
PCR
What does PCR result provide in diagnosis of H.pylori ?
Highly sensitive & specific test provide rapid results & information regarding antibiotic resistance
(e.g., identify specific mutations)
Important properties of Norwalk virus ( Caliciviruses; Norovirus)
- Nonsegmented, single-stranded, positive polarity RNA genome
- Nonenveloped virus with icosahedral nucleocapsid
- No polymerase within virion
- Electron microscope : 10 spikes & 32 cup-shaped depressions
- Six genogroups
- Genogroup II —-> most human infections
Transmission of Norovirus
- Fecal–oral route —-> ingestion of contaminated seafood or water
- Outbreaks occur in group settings :
such as cruise ships , schools , hospitals etc - Person-to-person transmission occurs in group settings
When does the New strains of Norwalk virus appear ?
every 2 to 4 years —-> widespread infections
What are the features of Norwalk virus that helps it in transmission?
- Low infectious dose
- Excretion of virus in stool :
* both before onset of symptoms & for several weeks after recovery - Resistance to inactivation by chlorination & drying in environment
- Infectious for several days in water
- Uncooked food
- environmental surfaces such as door handles
Infection is limited to which type of cell in Norovirus?
mucosal cells of intestinal tract
Clinical findings of Norovirus
- Watery diarrhea :
* without red cells or white cells - Sudden onset of vomiting & diarrhea
- low-grade fever & abdominal cramping
- chronic gastroenteritis ( in immunocompromised patients)
- signs of central nervous system involvement such as headache, meningismus & photophobia ( in outbreaks)
Diagnosis of Norwalk virus
- Diagnosis is clinical.
* Polymerase chain reaction (PCR) test on stool
