Week 3 - GIT disorders continued Flashcards
What is some of the epidemiology of Salmonella gastroenteritis?
- Source usually animals
- Vehicle usually food (temp abuse)
- Humans excrete for a week or two after infection but are rarely long-term carriers.
- Occasionally acquired from another person.
What is the infective dose required for Salmonella gastroenteritis?
Greater than 10^5 organisms (high infective dose)
If Salmonella spp. gets killed by stomach acid, how do numbers high enough to cause disease pass through?
Pass through in food masses.
Which areas of the GIT do Salmonella spp. attach to and then enter cells?
Small intestine and colon.
What are the clinical symptoms of Salmonella gastroenteritis?
Nausea and vomiting followed by diarrhoea and fever. Complete recovery
What is the incubation period of Salmonella gastroenteritis?
1-2 days
What is the duration period of Salmonella gastroenteritis?
3-7 days
What is the treatment for Salmonella gastroenteritis?
Fluids and electrolytes.
Antibiotics if septicaemia is present.
What are Virulence plasmids in Salmonella?
Many serovars of Salmonella possess plasmids which are essential for salmonellae to produce systemic disease.
Virulence plasmids range in size from 50 to 90kb.
They have a highly conserved region of approximately 8kb encompassing five genes which are related to virulence.
The genes are now designated spvRABCD (salmonella plasmid virulence)
What are some discoveries about antibiotic resistance in Salmonella?
- Salmonella genomic isalnd 1 (SGI1) is the first genomic island reported to contain an antibiotic resistance gene cluster
- It was identified in the multidrug-resistant Salmonella enterica serovar Typhimurium DT104.
The antibiotic resistance genes are clustered in a 13-kb segment within a 43-kb genomic island.
All resistance genes are contained within a complex integron structure. - One study found that 60% of meat is contaminated with Salmonella. Half of isolated had resistance to more than one class of drug. One isolated was multi-drug resistant.
What are some of the general characteristics of Campylobacter?
- Small, curved motile
- Gram negative rods
- Microaerophillic (5% O2) - fastidious
- Most pathogenic speicies are thermophillic as they are naturally found in the GIT of pultry @ 43 degrees.
- Exhibit darting motility - move in corkscrew fashion which helps to get through the intestinal mucous.
- Coccoid forms develop in older cultures which are viable but not about to be cultured.
- Has a small genome.
What are some of the most common types of Campylobacter?
C. jejuni, C. coli, C. fetus. C. lari, C, upsaliensis.
What are some of the symptoms of Campylobacter?
May be subclinical or may cause disease of varying severity.
C. jejuni infection typicall yresults in abdominal pain, fever and diarrhoea which may be mucopurulent or bloddy
What are some unusual disease manifestations of Campylobacter?
Campylobacter has been associated with rare sequelae including reactive arthritis and Guillain-Barre syndrome.
Human infection with C. fetus may cause localised abscesses or generalised sepsis particularly in immunosuppressed persons.
How does transmission of Campylobacter occur?
- Commensal of birds are of the most common causes of gastroenteritis
- Up to 85% of chickens infected
- ~95% of chicken products are contaminated
- Sources of infection included unpasteurised milk, water, pets, young adults and children.
What is the basic pathogenesis of Campylobacter?
- After ingestion is passes through the stomach protected by food masses
- C. jejuni is killed by acid in stomach
- Infective dose 100 bacteria
- Main site of colonisation is the jejunum but the colon may also be involved.
- Penetrates mucosa and invades lamina propria where it damages the epithelium and causes symptoms.
How do Campylobacter bacteria get into the host cell?
- Attaches to the epithelial lining using its’ flagella.
- Once attached to surface of cell it produces a protein called CadF. This binding triggers rearrangement of the host cytoskeleton.
- At this point they also secrete HTRA enzyme which breaks down tight junctions. This might allow the bacteria to move between the tight junctions and then infect cells from underneath like Shigella.
- Signalling pathways in the host cell are activated which cause actin to rearrange and take up the C.jejuni into a vacuole.
- Inside the cell, the production of toxin blocks the transition to the G2 phase ultimately causing cell death.
- Damage to the epithelial lining caused the sub-mucosa to be exposed leading to blood in the stool.
What are some of the immunological complications of Campylobacter?
Guillain Barre Syndrome (C. jejuni most common) Generalised paralysis (acute/chronic) Reactive Arthritis (C. jejuni, C. coli, C. concisus)
How does Campylobacter infection cause generalised paralysis?
Because of antigenic mimicry between LPS and human gangliosides that are found on the surface of neurons, patients can develop antibodies which attack neurons causing neurological symptoms. this can lead to generalized acute or chronic paralysis and pain.
What is the treatment for Campylobacter infection?
Management of symptoms
Fluid replacement only in mild cases
Severe cases may require treatment with erythromycin or clarithromycin.
What biochemical tests might be performed to identify Campylobacter?
Catalase H2S prudction i n triple sugar agar Growth at 25C, 42C to distinguish species Sensitivity to nalidixic acid and cephalothin Hippurate hydrolysis Nitrate reduction Growth in 1% glycerine Indoxyl acetate hydrolysis
What are some antibiotics that Campylobacter has shown resistance to?
Tetracyline Erythromycin Ciprofloxacin Kanamycin Nalidixic acid Chloramphenicol
What are the four significant groups of virus types which cause viral gastroenteritis?
Rotaviruses
Caliciviruses i.e. Norovirus, Sapporo virus
Astroviruses
Enteric adenoviruses
How common is viral gastroenteritis and who is most affected?
Extremely common. 95% of children are infected with Rotavirus by 5 years.
Children in developing countries = major cause of death
Adults = norovirus, usually a common source i.e. seafood
