MI: GI infections Flashcards
1
Q
List some reportable GI infections
A
- Camplybacter
- Escherichia coli O157
- Salmonella
- Shigella
- Listeria
2
Q
What are the main characteristics of secretory diarrhoea? What are some causes?
A
- No fever/low grade fever
- No inflammatory cells in stool
- Causes: Vibrio Cholera (rice-water stool), E-Coli (traveller’s), Staph aureus (same/next day Sx), Bacillus cereus (reheated rice)
3
Q
What are the main characteristics of inflammatory diarrhoea? What are some causes?
A
- Fever
- Inflammatory cells present in stool (neutrophils)
- Causes (Remember CHESS organisms): Campylobacter jejuni, Haemorrhagic E.Coli, Entamoeba histolytica,Shigella, Salmonella enteritides (non-typhoidal), Shigella
Also known as exudative diarrhoea
4
Q
List some examples of severe GI infections that produce a fever with little stool changes.
A
Also known as enteric fever
- Salmonella typhi
- Yersinia enterocolitca -> often causes terminal ileitis and adenitis, can resemble appendicitis
- Brucella
White blood cells are present in stool (mononuclear cells)
5
Q
Describe the mechanism by which Vibrio cholerae causes secretory diarrhoea.
A
- 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.
6
Q
What are superantigens?
A
- 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
7
Q
How does the host immune response determine in inflammatory respone to enteropathic bacteria?
A
8
Q
What type of organism is Staphylococcus aureus?
A
- Gram-positive coccus
- Catalase and coagulase positive
- Appears in clusters
9
Q
What type of toxin is produced by Staphylococcus aureus?
A
Enterotoxin - this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2
10
Q
How is Staphylococcus aureus spread and what kind of GI symptoms can it cause?
A
- 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
11
Q
What type of organisms is Bacillus cereus?
Associated food?
A
Gram-positive rods that are spore-forming
Spores germinate in reheated rice
12
Q
What type of toxins does B. cereus produce?
A
- Heat-stable emetic toxin
- Heat-labile diarrhoeal toxin
13
Q
What type of GI symptoms does B. cereus cause?
A
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
14
Q
Name three types of Clostridium infection
A
- Clostridium botulinum
- Clostridium perfringens
- Clostridium difficile
15
Q
What kind of infection does Clostridium botulinum cause?
Associated foods?
Treatment?
A
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
16
Q
What kind of infection does Clostridium perfringens cause?
A
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
17
Q
What kind of infection does C. difficile cause?
A
Pseudomembranous colitis
- Hospital-acquired infection related to antibiotic use
18
Q
Which antibiotics are most commonly implicated in C. difficile colitis?
A
- Cephalosporins
- Clindamycin
- Ciprofloxacin
19
Q
How is C. difficile colitis treated?
A
- Metronidazole, vancomycin
- Stop the offending antibiotic
20
Q
What type of organism is Listeria monocytogenes?
A
- Gram positive, rod-shaped, facultative anaerobe
- Beta-haemolytic, aesculin-positive with tumbling motility
21
Q
What is the source of Listeria?
A
Grows are 4 degrees so refrigerated foods (cold enhancement)
- Unpasteurised dairy
- Vegetables
22
Q
What GI symptoms does Listeria tend to cause? Which patients groups are particularly susceptible?
A
- Fever, watery diarrhoea, cramps, headache and NO vomiting
- Neonates, immunocompromised
23
Q
How is Listeria infection treated?
A
Ampicillin
24
Q
What type of organisms are Enterobacteriaceae and name some examples?
A
- Facultative anaerobes
- Lactose fermenters
- Oxidase-negative
- Escherichia coli, Salmonella, Shigella, Klebsiella
25
Name and describe the different types of *E. coli* infection.
* **ETEC** - toxigenic, main cause of travellers' diarrhoea
* **EPEC** - pathogenic, infantile diarrhoea -> **P** for **P**aeds
* **EIEC** - invasive, dysentry
* **EHEC** - haemorrhagic, caused by *E. coli* 0157:H7
## Footnote
Avoid antibiotic treatment
26
Where does *E. coli* act?
Jejunum, ileum but NOT colon
27
Which toxin causes haemolytic uraemic syndrome?
EHEC shiga-like verocytotoxin
28
What type of bacteria are *Salmonellae?*
- Gram-negatives, Non-lactose fermenting,
- Produce hydrogen suphide (form black colonies)
- Grows on TSI agar, XLD agar and selenite F broth
29
Which antigens are found on *Salmonellae?*
* LPS **O antigen** (groups A-I)
* Flagellar **H antigen**
* Capular **Vi antigen** (virulence, antiphagocytic)
## Footnote
NOTE: differences in these antigens help identify the serotypes of *Salmonellae*
30
List 2 main species of *Salmonella*.
* *Salmonella typhi*
* *Salmonella enterica*
31
What are 2 important serotypes of *S. enterica*?
- *Salmonella enterica* serotype Enteritidis
- *Salmonella enterica* serotype Typhimurium
32
How is *Salmonella* Enteritidis transmitted?
Via infected poultry, eggs, meat
33
Describe the presentation of *Salmonella* Enteritidis.
Causes enterocolitis - self-limiting diarrhoea that is non-bloody
* Bacteraemia is rare
* Usually **no treatment required**
34
How is *Salmonella typhi* transmitted?
* Transmitted only by humans (faeco-oral)
* Multiplies in Peyer's patches and spreads via the endoreticular system
35
Describe the presentation of *Salmonella typhi.*
Causes typhoid fever with constipation
(rose coloured spots)
36
Which subset of patients are at increased risk of *Salmonella* bacteraemia?
Sickle cell patients
37
How is *Salmonella typhi* treated?
Ceftriaxone
38
What are some key microbiological features of *Shigella?*
(stains etc)
- Gram negative
- Non-lactose fermenter
- Does NOT produce hydrogen suphide
- Non-motile
39
Which antigens are seen on *Shigella?*
LPS O antigens
##FOOTNOTE
Polysaccharide (groups A-D) used to identify species
40
List some types of *Shigella.*
* *Shigella sonnei*
* ***Shigella dysenteriae***
* *Shigella flexneri* (MSM)
41
What is the most effective bacterial enteric pathogen and why?
*Shigella* - it has the lowest infective dose (50)
## Footnote
NOTE: Shigella has no animal reservoir and no carriers state
42
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**
43
What are the microbiological features of *Vibrio Cholerae?*
- Gram-negative
- Comma-shaped
- Late lactose-fermenters
- **Oxidase-positive**
44
What are the different groups of *Vibrio cholerae?*
* O1 - causes epidemics
* Non-O1 - sporadic, non-pathogens
45
How is *Vibrio cholerae* transmitted?
Contamination of water and food from human faeces
46
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
47
Name and describe the key features of other types of *Vibrio.*
How is it treated?
***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**
48
What are the main microbiological features of *Campylobacter?*
* Gram negative
* Comma-shaped
* Microaerobphilic
* Oxidase-positive
* Motile
49
How is *Campylobacter* transmitted?
Transmitted via ingestion of **food and water contaminated with animal faeces**
50
Describe the presentation of *Campylobacter jejuni* infection.
- Watery, foul-smelling diarrhoea, bloody stools, fever and severe abdominal pain
51
How is *Campylobacter* infection treated?
Only treated if immunocompromised
- **Erythromycin or ciprofloxacin** if presenting within first 4-5 days
52
What are some complications of *Campylobacter* infection?
Guillian-Barre syndrome
Reactive arthritis
53
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*)
54
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
55
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**
56
Describe the presentation of GI infection by *Entamoeba histolytica.*
* Dysentry
* Flatulence
* Tenesmus
* Liver abscess
## Footnote
Chronic infection can cause weightloss +/- diarrhoea
57
How is *Entamoeba histolytica* infection diagnosed and treated?
* Diagnosis: stool microscopy (wet-mount, iodine and trichrome), serology of invasive disease
* Treatment: **metronidazole** + paromomycin
58
What are the key microbiological features of *Giardia lamblia?*
* **Pear-shaped trophozoites**
* Two nuclei
* Four flagellae and a suction disc
59
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 -> steatorrhoea
60
How does *Giarda* infection present?
- Foul-smelling non-bloody diarrhoea,
- Cramps, flatulence,
- NO fever
- Proteins and fats in stool due to duodeum dysfunction-> **steatorrhoea**
61
How is *Giardia* infection diagnosed and treated?
* Stool microscopy
* ELISA
* String test
* Treatment: **metronidazole**
62
What are the main features of *Cryptosporidium parvum?*
What stain is used?
* **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
63
What is the predominant strain of norovirus?
GII4
64
What is rotavirus and what does it cause?
* dsDNA virus
* Replicates in the mucosa of the small intestine
* Causes secretory diarrhoea with no inflammation
## Footnote
NOTE: exposure to natural infection twice will confer lifelong immunity
65
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**
## Footnote
Transmitted via faeco-oral route
66
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)
67
Who is responsible for collecting reports of diarrhoeal illness and identifying outbreaks?
Health Protection Unit (HPU)
68
A fine art student travels to New York, where he eats scrambled eggs.
12 hours later, he becomes unwell with profuse diarrhoea. There is no blood. He has diffuse abdominal pain with pain that comes and goes in waves.
What organism is likely responsible for his symptoms?
Salmonella enterica
## Footnote
Salmonella enterica is commonly associated with foodborne illness and can cause symptoms such as vomiting, diarrhea, and abdominal pain.
The consumption of undercooked eggs is a known risk factor for Salmonella enterica infection.
A possible differential is campylobacter, but this is typically associated with undercooked chicken and often produces bloody diarrhoea.
Staphylococcus aureus typically has a more rapid onset (1-2 hours). Viral gastroenteritis often isn't preceded by a foodborne trigger, as the incubation period is days.
69
What is the most common causative organism of diarrhoea in returning travellers to the UK?
Escherichia coli (ETEC)
70
What gram positive organism is associated with tumbling motility and rockets?
Listeria monocytogenes
