MI: GI infections Flashcards
List some reportable GI infections
- Camplybacter
- Salmonella
- Shigella
- Escherichia coli O157
- Listeria
What are the main characteristics of secretory diarrhoea?
Watery diarrhoea (no inflammatory cells in stool)
No fever
What are the main characteristics of inflammatory diarrhoea?
Fever
Diarrhoea (inflammatory cells present, may be bloody)
List some examples of severe GI infections that produce a fever with little stool changes.
- Salmonella typhi
- Enteropathogenic Yersinia
- Brucella
Describe the mechanism by which Vibrio cholerae causes secretory diarrhoea.
- The cholera toxin has subunits A and B which stimulate adenylate cyclase.
- This leads to the production of cAMP which opens chloride channels on the membranes of enterocytes.
- Chloride efflux into the lumen is accompanied by water and electrolyte loss.
What are superantigens?
Toxins that bind to TCR outside the peptide binding region.
They cause large scale activation of T cells leading to massive cytokine production by CD4 cells.
What type of organism is Staphylococcus aureus?
Catalase and coagulase positive, Gram-positive coccus that appears in clusters
What type of toxin is produced by Staphylococcus aureus?
Enterotoxin - this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2
How is Staphylococcus aureus spread and what kind of GI symptoms can it cause?
Spread by skin lesions on food handlers
Causes prominent vomiting and watery, non-bloody diarrhoea
NOTE: it is self-limiting so does not require treatment
What type of organisms is Bacillus cereus?
Gram-positive rods that are spore-forming
What type of toxins does B. cereus produce?
- Heat stable emetic toxin
- Heat labile diarrhoeal toxin
What type of GI symptoms does B. cereus cause?
Watery, non-bloody diarrhoea
NOTE: it can cause bacteraemia and cerebral abscesses in vulnerable populations
Name three types of Clostridium infection and describe the diseases that they cause.
Clostridium botulinum - causes botulism
- From canned food
- Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses resulting in paralysis
- Treated with antitoxin
Clostridium perfringens - food poisoning
- From reheated food
- Generates a superantigen that mainly affects the colon
- Causes watery diarrhoea and cramps that last 24 hours
Clostridium difficile - pseudomembranous colitis
- Hospital-acquired infection related to antibiotic use
Which antibiotics are most commonly implicated in C. difficile colitis?
- Cephalosporins
- Clindamycin
- Ciprofloxacin
How is C. difficile colitis treated?
- Metronidazole
- Vancomycin
- Stop the offending antibiotic
What type of organism is Listeria monocytogenes?
Gram positive, rod-shaped, facultative anaerobe
Beta-haemolytic, aesculin-positive with tumbling motility
What GI symptoms does Listeria tend to cause?
Watery diarrhoea, cramps, headache, fever and a little vomiting
NOTE: it comes from refrigerated food (e.g. unpasteurised dairy)
How is Listeria infection treated?
Ampicillin
What type of organisms are Enterobacteriaceae?
- Facultative anaerobes
- Lactose fermenters
- Oxidase-negative
Name and describe the different types of E. coli infection.
- ETEC - toxigenic, main cause of travellers’ diarrhoea
- EPEC - pathogenic, infantile diarrhoea
- EIEC - invasive, dysentry
- EHEC - haemorrhagic, caused by E. coli 0157:H7
What causes haemolytic uraemic syndrome?
EHEC shiga-like verocytotoxin
What type of bacteria are Salmonellae?
Non-lactose fermenting, Gram-negatives
Produce hydrogen suphide (form black colonies)
Grows on TSI agar, XLD agar and selenite F broth
Which antigens are found on Salmonellae?
- Cell wall O (groups A-I)
- Flagellar H
- Capular Vi (virulence, antiphagocytic)
NOTE: differences in these antigens help identify types of Salmonellae
List three species of Salmonella.
- Salmonella typhi (and paratyphi)
- Salmonella enteritidis
- Salmonella choleraesuis
How is Salmonella transmitted?
Via infected meat products (but it can also be transmitted by pets (mainly reptiles))
Describe the presentation of Salmonella enteritidis.
- Enterocolitis - loose stools
- Transmitted by poultry, eggs and meat
- Self-limiting diarrhoea that is non-bloody
- No fever
- Bacteraemia is rare
Describe the presentation of Salmonella typhi.
- Transmitted only by humans
- Multiplies in Peyer’s patches and spreads via the endoreticular system
- Slow onset fever and constipation
- May cause splenomegaly, rose spots, anaemia and leucopaenia
- Blood cultures may be positive
Which subset of patients are at increased risk of Salmonella bacteraemia?
Sickle cell patients
How is Salmonella typhi treated?
Ceftriaxone
What are some key microbiological features of Shigella?
Non-lactose fermenter
Does NOT produce hydrogen suphide
Non-motile
Which antigens are seen on Shigella?
Cell wall O antigens
Polysaccharide (groups A-D)
List some types of Shigella.
- Shigella sonnei*
- Shigella dysenteriae*
- Shigella flexneri* (MSM)
What is the most effective bacterial enteric pathogen and why?
Shigella - it has the lowest infective dose (50)
NOTE: Shigella has no animal reservoir and no carriers
How does Shigella infection manifest?
Dysentry - severe diarrhoea with blood and mucus in the faeces
NOTE: Shigella produces shiga toxin
NOTE: avoid antibiotics when treating Shigella
What are the microbiological features of Vibrio?
Comma-shaped
Late lactose-fermenters
Oxidase-positive
Gram-negative
What are the different groups of Vibrio cholerae?
- O1 - causes epidemics
- Non-O1 - sporadic, non-pathogens
What type of GI disturbance does Vibrio cholerae cause?
Produce water diarrhoea without inflammatory cells
Treat the losses (water and electrolytes)
Name and describe the key features of other types of Vibrio.
Vibrio parahaemolyticus:
- Caused by ingestion of raw/undercooked seafood
- Causes self-limiting diarrhoea
- Grows on salty agar
Vibrio vulnificus:
- Causes cellulitis in shellfish handlers
- Can cause fatal septicaemia with D&V in HIV patients, treated with doxycycline
What are the main microbiological features of Campylobacter?
- Comma-shaped
- Microaerobphilic
- Oxidase-positive
- Gram-negative
- Motile
Descrie the presentation of Campylobacter jejuni infection.
Watery, foul-smelling diarrhoea, blood stools, fever and severe abdominal pain
NOTE: transmitted by food and water that has been contaminated by animal faeces
How is Campylobacter infection treated?
Only treated if immunocompromised
Erythromycin or ciprofloxacin
What are some complications of Campylobacter infection?
Guillian-Barre syndrome
Reactive arthritis
Which other bacterial organisms can cause GI disease?
- Yersinia enterocolitica - non-lactose fermenter that causes enterocolitis of mesenteric adenitis (also associated with reactive arthritis)
- Mycobacteria
What are the key microbiological features of Entamoeba histolytica?
- Motile trophozoite in diarrhoeal illness
- Non-motile cyst in non-diarrhoeal illness
- Killed by boiling
- Contains four nuclei
- No animal reservoir
Describe the pathophysiology of diarrhoeal illness caused by Entamoeba histolytica.
Ingestion of cysts → trophozoites move into the ileum → colonise the colon → causes flask-shaped ulcers
Describe the presentation of GI infection by Entamoeba histolytica.
- Dysentry
- Flatulence
- Tenesmus
- Liver abscess
How is Entamoeba histolytica infection diagnosed and treated?
- Diagnosis: stool microscopy, serology of invasive disease
- Treatment: metronidazole + paromomycin
What are the key microbiological features of Giardia lamblia?
- Pear-shaped trophozoites
- Two nuclei
- Four flagellae and a suction disc
Outline the pathophysiology of GI disease caused by Giardia.
- Transmitted by ingestion of cyst from faecally contaminated water
- Excystation in the duodenum leads to trophozoite attachment
- Results in malabsorption of protein and fat
- Presentation: foul-smelling non-bloody diarrhoea, cramps, flatulence, NO fever
how is Giardia infection diagnosed and treated?
- Stool microscopy
- ELISA
- String test
- Treatment: metronidazole
What are the main features of Cryptosporidium parvum?
- Causes severe diarrhoea in the immunocompromised
- Oocysts can be seen in the stool using modified Kinyoung acid fast stain
- Treated by boosting the immune system
What is the predominant strain of norovirus?
GII4
What is rotavirus and what does it cause?
- dsDNA
- Replicates in the mucosa of the small intestine and causes secretory diarrhoea with no inflammation
NOTE: exposure to natural infection twice will confer lifelong immunity
List some other viruses that can cause diarrhoeal illnesses.
- Adenovirus (types 40 and 41 can cause non-bloody diarrhoea in <2 year olds)
- Poliovirus
- Enterovirus (e.g. coxaskie, echovirus)
- Hepatitis A
Which causes of diarrhoeal illness have available vaccines?
- Cholera (serogroup O1)
- Campylobacter
- ETEC
- Salmonella typhi
- Rotavirus (rotarix (live, monovalent), rotateq (pentavalent), rotashield (used if risk of intussusception))
Who is responsible for collecting reports of diarrhoeal illness and identifying outbreaks?
Health Protection Unit (HPU)
