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MedEd + PathSoc + Laz's Qs + Romesh Path > Micro 2: GI infections > Flashcards

Micro 2: GI infections Flashcards

1
Q

List some reportable GI infections

A

Campylobacter

Salmonella

Shigella

Escherichia coli O157

Listeria

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2
Q

What are the main characteristics of secretory diarrhoea?

A

Watery diarrhoea (no inflammatory cells in stool)

No fever

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3
Q

What are the main characteristics of inflammatory diarrhoea v secretory?

A

Inflammatory:
Fever
Diarrhoea (inflammatory cells present, may be bloody)

Secretory:
Watery diarrhoea (no inflammatory cells in stool)
No fever

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4
Q

List some examples of severe GI infections that produce a fever with little stool changes.

A

Salmonella typhi

Enteropathogenic Yersinia

Brucella

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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

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6
Q

What are superantigens?

A

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

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7
Q

What type of toxin is produced by Staphylococcus aureus? what does this trigger

A

Enterotoxin – this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2

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8
Q

What type of organism is Staphylococcus aureus?

A

Catalase and coagulase positive, Gram-positive coccus that appears in clusters

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9
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 vomiting and watery, non-bloody diarrhoea

NOTE: it is self-limiting so does not require treatment

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10
Q

What type of organism is Bacillus cereus?

A

Gram-positive rods that are spore-forming

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11
Q

What type of toxins does B. cereus produce?

A

Heat stable emetic toxin

Heat labile diarrhoeal toxin

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12
Q

What type of GI symptoms does B. cereus cause?

A

Watery, non-bloody diarrhoea

NOTE: it can cause bacteraemia and cerebral abscesses in vulnerable populations

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13
Q

Name three types of Clostridium infection and describe the diseases that they cause.

A

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

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14
Q

Which antibiotics are most commonly implicated in C. difficile colitis?

A

Cephalosporins

Clindamycin

Ciprofloxacin

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15
Q

How is C. difficile colitis treated?

A

Metronidazole

Vancomycin

Stop the offending antibiotic

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16
Q

What type of organism is Listeria monocytogenes?

A

Gram-positive, rod-shaped, facultative anaerobe

Beta-haemolytic, aesculin-positive with tumbling motility

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17
Q

What GI symptoms does Listeria tend to cause?

A

Watery diarrhoea, cramps, headache, fever and a little vomiting

NOTE: it comes from refrigerated food (e.g. unpasteurised dairy)

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18
Q

How is Listeria infection treated?

A

Ampicillin

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19
Q

What type of organisms are Enterobacteriaceae?

A

Facultative anaerobes

Lactose fermenters

Oxidase-negative

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20
Q

Name and describe the different types of E. coli (GRAM -VE ROD) infection.

A

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

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21
Q

What causes haemolytic uraemic syndrome?

A

EHEC shiga-liked verocytotoxin

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22
Q

What type of bacteria are Salmonellae? what do they make on what agar?

A

Non-lactose fermenting, Gram-negatives

Produce hydrogen sulphide (form black colonies)

Grows on TSI agar, XLD agar and selenite F broth

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23
Q

Which antigens are found on Salmonellae?

A

Cell wall O (groups A-I)

Flagellar H

Capsular Vi (virulence, antiphagocytic)

NOTE: differences in these antigens help identify types of Salmonellae

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24
Q

List three species of Salmonella.

A

Salmonella typhi (and paratyphi)
Salmonella enteritidis
Salmonella choleraesuis

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25
How is Salmonella transmitted?
Via infected meat products (but it can also be transmitted by pets (mainly reptiles))
26
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
27
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
28
Which subset of patients are at increased risk of Salmonella bacteraemia?
Sickle cell patients
29
How is Salmonella typhi treated?
Ceftriaxone
30
What are some key microbiological features of Shigella?
Non-lactose fermenter Does NOT produce hydrogen sulphide Non-motile
31
Which antigens are seen on Shigella?
Cell wall O antigens Polysaccharide (groups A-D)
32
List some types of Shigella.
Shigella sonnei Shigella dysenteriae Shigella flexneri (MSM)
33
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
34
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
35
What are the microbiological features of Vibrio?
Comma-shaped Late lactose-fermenters Oxidase-positive Gram-negative CLOG = vibrio
36
What are the different groups of Vibrio cholerae?
O1 – causes epidemics Non-O1 – sporadic, non-pathogens
37
What type of GI disturbance does Vibrio cholerae cause? mx?
Produce watery diarrhoea without inflammatory cells Treat the losses (water and electrolytes)
38
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
39
What are the main microbiological features of Campylobacter?
Comma-shaped Microaerobphilic Oxidase-positive Gram-negative Motile
40
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
41
How is Campylobacter infection treated?
Only treated if immunocompromised Erythromycin or ciprofloxacin
42
What are some complications of Campylobacter infection?
Guillain-Barre syndrome Reactive arthritis
43
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
44
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
45
Describe the presentation of GI infection by Entamoeba histolytica.
Dysentery, flatulence, tenesmus, liver abscess
46
How is Entamoeba histolytica infection diagnosed and treated?
Diagnosis: stool microscopy, serology of invasive disease Treatment: metronidazole + paromomycin
47
What are the key microbiological features of Giardia lamblia?
Pear-shaped trophozoites Two nuclei Four flagellae and a suction disc
48
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
49
How is Giardia infection diagnosed and treated?
Stool microscopy ELISA String test Treatment: metronidazole
50
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
51
What is the predominant strain of norovirus?
GII.4
52
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
53
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
54
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))
55
Who is responsible for collecting reports of diarrhoeal illness and identifying outbreaks?
Health Protection Unit (HPU)
56
Main cause of gastroenteritis?
Viral
57
Ix of suspected c.diff? of protazoa or parasite?
``` Stool MCS (standard) + C. Diff toxins +/- OCP - ova, cysts and parasite test (protazoa / parasites) ```
58
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
59
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)
60
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
61
Deadliest strain of C. Diff?
Ribotype 027
62
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
63
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
64
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
65
What organism is responsible for ANCHOVY PASTE CONSISTENCY on US guided draingae of Liver abscess?
Entamoeba Histolytica
66
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
67
Comma-shaped organism that is associated with Guillain-Barre and Reactive arthritis? what is another organism that is comma-shaped?
Campylobacter Jejuni Vibrio cholerae
68
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
69
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
70
What type of salmonella is associated w/ poultry? main symptom? mx?
Salmonella Enteritidis Causes bloody diarrhoea mx = ciprofloxacin
71
Most common cause of travellers diarrhoea?
Escherichia coli | Enterotoxigenic e. coli - ETEC
72
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?
73
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
74
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)
75
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 =
76
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)
77
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
78
MoA of C. diff?
Toxin A -enterotoxin + Toxin B -cytotoxic -> Causes pseudomembranous colitis
79
What are the causes of BLOODY DIARRHOEA?
CHESS ``` Campylobacter Haemorrhagic E.coli (0157 -> HUS) Entamoeba histolytic Salmonella Shigella ```
80
What is generally given to gram -ve causes of gastroenteritis?
Ciprofloxacin

MedEd + PathSoc + Laz's Qs + Romesh Path (99 decks)

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