MI: GI infections Flashcards
List some reportable GI infections
- Camplybacter
- Salmonella
- Shigella
- Escherichia coli O157
- Listeria
What are the main characteristics of secretory diarrhoea? What are some causes?
- No fever/low grade fever
- No inflammatory cells in stool
- Causes: Vibrio Cholera, ETEC
What are the main characteristics of inflammatory diarrhoea? What are some causes?
- Fever
- Inflammatory cells present in stool (neutrophils)
- Causes: Campylobacter jejuni, Shigella, non-typhiodal Salmonella, EIEC
Also known as exudative diarrhoea
List some examples of severe GI infections that produce a fever with little stool changes.
Also known as enteric fever
- Salmonella typhi
- Enteropathogenic Yersinia
- Brucella
White blood cells are present in stool (mononuclear cells)
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 and MHC outside the peptide binding region
- This leads to non-specific activation and large-scale polyclonal expansion of T cells with massive cytokine production
- Results in systemic toxicity and suppression of adaptive immune response
How does the host immune response determine in inflammatory respone to enteropathic bacteria?
What type of organism is Staphylococcus aureus?
- Gram-positive coccus
- Catalase and coagulase positive
- 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 nausea and vomiting (occasionally watery diarrhoea)
- Self-limiting (resolution within 24 hours) so does not require treatment
What type of organisms is Bacillus cereus?
Gram-positive rods that are spore-forming
Spores germinate in reheated rice
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?
Diarrhoeal type - watery, non-bloody diarrhoea; abdominal cramping
Emetic type - nausea and vomiting (sometime diarrhoea as well)
NOTE: it can cause bacteraemia and cerebral abscesses in vulnerable populations
Name three types of Clostridium infection
- Clostridium botulinum
- Clostridium perfringens
- Clostridium difficile
What kind of infection does Clostridium botulinum cause?
Causes botulism - ptosis, double vision, dysphagia, progessive muscle weakness and paralysis
- From canned food
- Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses resulting in paralysis
- Treated with antitoxin
What kind of infection does Clostridium perfringens cause?
Causes food poisoning - watery diarrhoea, cramps, but NO vomiting that lasts 24 hours
- From undercooking and poor storage of meat
- Part of normal colonic flora, but NOT small bowel
- Creates enterotoxic superantigen affects small bowel
What kind of infection does C. difficile cause?
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 is the source of Listeria?
Grows are 4 degrees so refrigerated foods (cold enhancement)
- Unpasteurised dairy
- Vegetables
What GI symptoms does Listeria tend to cause? Which patients groups are particularly susceptible?
- Fever, watery diarrhoea, cramps, headache and NO vomiting
- Neonates, immunocompromised
How is Listeria infection treated?
Ampicillin
What type of organisms are Enterobacteriaceae and name some examples?
- Facultative anaerobes
- Lactose fermenters
- Oxidase-negative
- Escherichia coli, Salmonella, Klebsiella, Shigella
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
Avoid antibiotic treatment
Where does E. coli act?
Jejunum, ileum but NOT colon
Which toxin 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?
- LPS O antigen (groups A-I)
- Flagellar H antigen
- Capular Vi antigen (virulence, antiphagocytic)
NOTE: differences in these antigens help identify the serotypes of Salmonellae
List 2 main species of Salmonella.
- Salmonella typhi
- Salmonella enterica
What are 2 important serotypes of S. enterica?
- Salmonella enterica serotype Enteritidis
- Salmonella enterica serotype Typhimurium
How is Salmonella Enteritidis transmitted?
Via infected poultry, eggs, meat
Describe the presentation of Salmonella Enteritidis.
Causes enterocolitis - self-limiting diarrhoea that is non-bloody
- Bacteraemia is rare
- Usually no treatment required
How is Salmonella typhi transmitted?
- Transmitted only by humans
- Multiplies in Peyer’s patches and spreads via the endoreticular system
Describe the presentation of Salmonella typhi.
Causes typhoid fever with constipation
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?
- Gram negative
- Non-lactose fermenter
- Does NOT produce hydrogen suphide
- Non-motile
Which antigens are seen on Shigella?
LPS O antigens
Polysaccharide (groups A-D) used to identify species
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 state
How does Shigella infection manifest? How do you treat it?
Dysentry
- Severe diarrhoea with blood and mucus in the faeces
- Invades the cells of the distal ileum and colon
- Produces shiga toxin
Avoid antibiotics when treating, however use ciprofloxacin if required
What are the microbiological features of Vibrio?
- Gram-negative
- Comma-shaped
- Late lactose-fermenters
- Oxidase-positive
What are the different groups of Vibrio cholerae?
- O1 - causes epidemics
- Non-O1 - sporadic, non-pathogens
How is Vibrio cholerae transmitted?
Contamination of water and food from human faeces
What type of GI disturbance does Vibrio cholerae cause and how do you treat it?
- Produces massive watery (secretory) diarrhoea without inflammatory cells
- Treat by replacing the water and electrolytes lost
Name and describe the key features of other types of Vibrio.
Vibrio parahaemolyticus:
- Caused by ingestion of raw/undercooked seafood
- Causes self-limiting diarrhoea (3 days)
- Grows on salty agar
Vibrio vulnificus:
- Causes cellulitis in shellfish handlers
- Can cause fatal septicaemia with diarrhoea and vomiting in HIV patients
Treat both with doxycycline
What are the main microbiological features of Campylobacter?
- Gram negative
- Comma-shaped
- Microaerobphilic
- Oxidase-positive
- Motile
How is Campylobacter transmitted?
Transmitted via ingestion of food and water contaminated with animal faeces
Descrie the presentation of Campylobacter jejuni infection.
- Watery, foul-smelling diarrhoea, bloody stools, fever and severe abdominal pain
How is Campylobacter infection treated?
Only treated if immunocompromised
- Erythromycin or ciprofloxacin if presenting within first 4-5 days
What are some complications of Campylobacter infection?
Guillian-Barre syndrome
Reactive arthritis
Which other bacterial organisms can cause GI disease?
Yersinia enterocolitica
- Non-lactose fermenting
- Transmitted via food contaminated with faeces of domestic animals
- Causes enterocolitis and mesenteric adenitis
- Also associated with reactive arthritis
Mycobacteria (M. Tuberulosis, Avium, Intracellulare)
What are the key characteristics of Entamoeba histolytica?
- Motile trophozoite in diarrhoeal illness
- Non-motile cyst in non-diarrhoeal illness
- Killed by boiling, removed via water filters
- 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
Chronic infection can cause weightloss +/- diarrhoea
How is Entamoeba histolytica infection diagnosed and treated?
- Diagnosis: stool microscopy (wet-mount, iodin and trichrome), 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
How does Giarda infection present?
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?
- Protozoa that 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 virus
- Replicates in the mucosa of the small intestine
- 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) - diagnosed via PCR or stool antigen detection
- Poliovirus
- Enterovirus (e.g. coxaskie, echovirus)
- Hepatitis A
Transmitted via faeco-oral route
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)
