Micro 2: GI infections Flashcards
List some reportable GI infections
Campylobacter
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 v secretory?
Inflammatory:
Fever
Diarrhoea (inflammatory cells present, may be bloody)
Secretory:
Watery diarrhoea (no inflammatory cells in stool)
No fever
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 toxin is produced by Staphylococcus aureus? what does this trigger
Enterotoxin – this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2
What type of organism is Staphylococcus aureus?
Catalase and coagulase positive, Gram-positive coccus that appears in clusters
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 organism 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 (GRAM -VE ROD) infection.
ETEC (enterotoxigenic) – toxigenic, main cause of travellers’ diarrhoea
EPEC (Enteropathogenic) – pathogenic, infantile diarrhoea
EIEC (Enteroinvasive) – invasive, dysentery
EHEC (Enterohaemorrhagic) – haemorrhagic, caused by E. coli O157:H7
What causes haemolytic uraemic syndrome?
EHEC shiga-liked verocytotoxin
What type of bacteria are Salmonellae? what do they make on what agar?
Non-lactose fermenting, Gram-negatives
Produce hydrogen sulphide (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
Capsular 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 - where does it multiply
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 sulphide
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? what does it produce? mx?
Dysentery – 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
CLOG = vibrio
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? mx?
Produce watery 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
Describe the presentation of Campylobacter jejuni infection? transmission
Watery, foul-smelling diarrhoea, bloody 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?
Guillain-Barre syndrome
Reactive arthritis
Which other bacterial organisms can cause GI disease?
Yersinia enterocolitica – non-lactose fermenter that causes enterocolitis or mesenteric adenitis (also associated with reactive arthritis)
Mycobacteria
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.
Dysentery, 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 pathophysiologiy 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? stain? mx?
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?
GII.4
What is rotavirus and what does it cause?
dsRNA virus
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. coxasckie, 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)
Main cause of gastroenteritis?
Viral
Ix of suspected c.diff? of protazoa or parasite?
Stool MCS (standard) \+ C. Diff toxins \+/- OCP - ova, cysts and parasite test (protazoa / parasites)
Mx of gastroenteritis ?
Conservative:
- Side room, PPE, wash hands
- IV fluids, electrolytes, oral rehydration
Medical:
Loperamide (CI in Abx-assc colitis, fever and PR bleeding)
Ciprofloxacin (given empirically in severe / known bacterial) - strong v gram -ve
An elderly woman has type 6 stool which is green and mucoid in appearance. She is on the 6th day of IV ceftriaxone (=cephalosporin).
What is the likely causative organism?
Clostridium difficile
RFs in this case:
- Abx starting w/ C (co-amoxiclav, cephalosporins, clindamycin)
What causes pseudomembranous colitis?
What is the treatment + alternatives?
C. Diff - treated w/ PO Vancomycin- better for severe (also PO Metronidazole)
Alternative - faecal transplant
Surgical - Colectomy
Deadliest strain of C. Diff?
Ribotype 027
Infants under 12 months should not be fed honey due to an increased risk of food poisoning caused by which of organism? What unusual symptom is suggestive of this? Mx?
Clostridium Botulinum - RF = Honey (vaccum packed foods) (Gram+Ve)
Causes descending paralysis - Toxin blocks ACh release from peripheral nerves
Mx:
• Anti-toxin IM injections
A woman develops vomiting a few hours after reheating and ingesting Chinese fried rice.
What is the most likely causative organism? Incubation?
Bacillus cerus - RF = Reheated rice (often chinese fried in Qs) (gram +ve)
Quick incubation period - often symptoms on same day
A South American man presents to a doctor in the UK with fever and bloody
diarrhoea. Investigations reveal a cyst in the right lobe of the liver.
What is the most likely causative organism? What unusual symptoms does this cause? Mx?
Entamoeba histolytica - HAS 4 NUCLEI (Parasite)
Can cause liver abscesses and (flask-shaped) ulcers in caecum
Mx:
- Metronidazole (useful for parasite) + paromomycin
- Liver abscess = US guided drainage
What organism is responsible for ANCHOVY PASTE CONSISTENCY on US guided draingae of Liver abscess?
Entamoeba Histolytica
A man develops foul-smelling diarrhoea and cramping pain 5 days after eating chicken at his neighbour’s barbeque.
What is the most common causative organism? Symptoms? Mx?
A) Campylobacter jejuni B) Shigella C) Escherichia coli 0157 D) Salmonella typhi E) Vibrio cholerae
Campylobacter jejuni - RF = Poultry (GRAM -VE)
Symptoms:
- CHESS - Bloody diarrhoea
- CRAMPY abdo pain - SBA land for campylobacter
- Watery diarrhoea
Mx?
Macrolide eg. clarithromycin
Comma-shaped organism that is associated with Guillain-Barre and Reactive arthritis? what is another organism that is comma-shaped?
Campylobacter Jejuni
Vibrio cholerae
An aid worker returns from camp in Yemen. He has profuse watery diarrhoea,
which he describes as looking like water that rice has been cooked in. He is very dehydrated.
What is the likely cause of his diarrhoea? Symptoms -pathognmonic?
Vibrio Cholerae - RF = Africa + Middle East
Symptoms:
- (Profuse) watery diarrhoea
= RICE WATER STOOLs
A 42 year old man who recently returned from a trip to India has presented with a fever of 39.6°C and abdominal pain but no history of diarrhoea. His blood cultures
have grown Gram-negative bacilli and his Malaria rapid diagnostic test is negative.
What is the most appropriate antibiotic therapy? What organism? What if they develop diarrhoea after mx?
Gram-ve bacilli + RF = Travel from India (+ Africa) -> Salmonella Typhii
Symptoms:
- Constipation
- Rose spots
Mx:
Ceftriaxone (+ azithromycin) -> if develop diarrhoea consider C. Diff
What type of salmonella is associated w/ poultry? main symptom? mx?
Salmonella Enteritidis
Causes bloody diarrhoea
mx = ciprofloxacin
Most common cause of travellers diarrhoea?
Escherichia coli
Enterotoxigenic e. coli - ETEC
A boy presents with diarrhoea, unexplained bruises all over his body and feeling fatigued. He recently visited his grandparents in Wiltshire.
What is the most likely causative organism?
This is Haemolytic Uraemic Syndrome which can be caused by E. Coli 0157 (GRAM -VE)
Mention of Wiltshire - countryside = likely to pick up this variant from farm animals?
A nurse on the care of the elderly ward complains of vomiting and diarrhoea. She
mentions that many of her patients also had similar symptoms.
What is the most likely causative organism?
A) Cryptosporidium parvum B) Rotavirus C) Adenovirus D) Norovirus E) Staphylococcus aureus
Norovius AKA winter vomiting bug that is associated w/ outbreaks (hospitals + nursing homes) -> D+V
Organisms other than Norovirus that can cause vomiting + in who?
Rotavirus can also cause vomiting however is vaccinated for hence consider in young children - may not be vaxd or antivax
Adenovirus - RF = Immunocompromised or poor hygiene (faeca-oral transmission)
A HIV-positive patient presents with long-standing diarrhoea. A stool sample is
sent for analysis and the organism is visualised after Kinyoun staining.
What is the most likely causative organism? RFs, symptoms and ix?
A) Cryptosporidium parvum B) Giardia lamblia C) Entamoeba histolytica D) Adenovirus E) Staphylococcus aureus
A) Cryptosporidium parvum
Long-standing diarrhoea - generally points towards a parasitic cause and Kinyoun staining is linked w/ Cryptosporidium parvum
RF = Immunocompromised
Symptoms = prolonged diarrhoea
Ix =
A HIV-positive patient presents with long-standing diarrhoea. A stool sample is
sent for analysis and the organism is visualised after Kinyoun staining.
What is the most likely causative organism? RFs, symptoms and ix?
A) Cryptosporidium parvum B) Giardia lamblia C) Entamoeba histolytica D) Adenovirus E) Staphylococcus aureus
A) Cryptosporidium parvum
Long-standing diarrhoea - generally points towards a parasitic cause and Kinyoun staining is linked w/ Cryptosporidium parvum
RF = Immunocompromised
Symptoms = prolonged diarrhoea
Ix = Stool OCP + Kinyoun stain
Mx = Paromomycin + improve immunity (eg HIV mx)
Giardia lamblia - RFs, Symptoms, Ix, Mx, Pathgmnoic term?
RF = Poor hygiene (faeco-oral)
+ Immunocompromised
Symptoms = Prolonged diarrhoea (watery, foul smelling)
Ix = Stool ELISA (more used), String test (more used in SBAs)
Mx = Metronidazole
Pathagnomnic = 2 pear-shaped nuclei
MoA of C. diff?
Toxin A -enterotoxin + Toxin B -cytotoxic -> Causes pseudomembranous colitis
What are the causes of BLOODY DIARRHOEA?
CHESS
Campylobacter Haemorrhagic E.coli (0157 -> HUS) Entamoeba histolytic Salmonella Shigella
What is generally given to gram -ve causes of gastroenteritis?
Ciprofloxacin
