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Pathology ICSM COPY > Microbiology 6 - GI infections > Flashcards

Microbiology 6 - GI infections Flashcards

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1
Q

In a febrile patient with a GI infection, what are the key differentials?

A
  1. Inflammatory diarroea
  2. If no diarrhoea - enteric fever (typhoid/ salmonella)
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2
Q

In an afebrile patient with a GI infection, what is the top differential?

A

Secretory diarrhoea due to toxins (eg cholera)

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3
Q

decribe the mechanism of cholera toxin

A

Subunit production

cAMP opens Cl- channels at apical membrane of enterocytes → Cl- efflux to lumen → loss of water and electrolytes → profoundly dehydrated

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4
Q

How to superantigens cause secretory diarrhoea?

A

bind directly to TCRs and MHC molecules; outside peptide binding site

massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response) → secretory diarrhoea

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5
Q

Why does staph aureus food poisoning produce such rapid symptoms?

A

Toxin is pre-formed

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6
Q

What are the key cytokines involved in Staph aureus food poisoning?

A

IL-7 and IL-2

produces enterotoxin, exotoxin that can act as a superantigen in GIT

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7
Q

How is S aureus food poisoning spread?

A

skin lesions on food handlers

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8
Q

Describe the microbiology of S aureus

A

catalase, coagulase +ve, gram +ve coccus

tetrads, clusters on gram stain → yellow colonies on blood agar

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9
Q

Describe the symptoms of S aureus food poisoning

A

Vomiting
Waterey, non-bloody diarrhoea

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10
Q

Describe the different toxins produced by bacilus cereus

A

Heat-stable toxin causes emesis
Heat-labile toxin causes diarrhoea
Only the heat-labile toxin is destroyed upon heating

spores in reheated rice

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11
Q

Describe the diarrhoea produced by bacilus cereus

A

Waterey, non-bloody

can cause cerebral abscesses

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12
Q

Describe the microbiology of bacillus cereus

A

Gram +ve rod-spores

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13
Q

In what type of food might clostridia botulinum be found?

A

canned or vacuum-packed food (honey in infants) - has preformed toxin(inactivated by cooking)

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14
Q

What is the MOA of Clostridium botulinum:

A

Blocks ACh release from peripheral nerve synapses: paralysis

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15
Q

What type of clostridia spp causes food poisoning?

A

Clostridia perfringens

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16
Q

In what sort of food is clostridia perfringens found?

A

reheated food (meat)

normal flora of colon but not small bowel, where the enterotoxin acts (superantigen)

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17
Q

Which organism causes pseudomembranous colitis?

A

Clostridium difficile

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18
Q

Which toxins are produced by C diff?

A

Toxin A = enterotoxin = inflammation

Toxin B = cytotoxin = virulence factor (more dangerous)

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19
Q

Which diarrhoeal disease is associated with antibiotic use?

A

Pseudomembranous colitis caused by C. difficile

any but mainly cephalosporins, cipro and clindamycin

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20
Q

what is the treatment for C diff

A

PO (to be absorbed by gut) vancomycin,

Stop cephs

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21
Q

What type of symptoms does listeria monocytogenes poisoning cause?

A

Febrile gastroenteritis

Watery diarrhoea, cramps, headache, fever, little vomiting

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22
Q

what is the treatment for listeria?

A

amoxicillin

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23
Q

Recall 2 sources of listeria poisoning

A

refrigerated food (“cold-enhancement”), unpasteurized dairy, vegetables (grows at 4ºC)

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24
Q

Is listeria alpha or beta haemolytic?

A

Beta haemolytic

aesculin positive with tumbling-weed motility

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25
What is the causative organism in 'traveller's diarrhoea'?
Enterobacteriacae (usually the toxogenic form, ETEC)
26
What enterotoxins are produced by e coli?
Heat labile stimulates adenyl cyclase and cAMP Heat stable stimulates guanylate cyclase Act on the jejunum/ileum not on colon
27
What organism causes haemolytic uraemic syndrome?
EHEC enterobacteriacae
28
Recall one very important thing to avoid in the management of enterobacteriacae poisoning
Antibiotics
29
Recall the microbiology of Salmonella
Non-lactose fermenters, H2S producers (black colonies), TSI agar, XLD agar, selenite F broth
30
Recall 3 worrying species of salmonella
S typhi S enteritidis S cholerasuis
31
What symptoms are caused by S typhi infection?
Bactaraemia Constipation and fever Splenomegaly and ROSE SPOTS anaemia, leucopaenia, bradycardia, haemorrhage
32
What are the 2 key forms of shigella that cause disease in humans?
``` S dysenteriae S flexneri (associated with MSM) ```
33
What disease pattern does shigella infection cause?
Dysentry -\> bloody diarrhoea Invading cells of mucosa of distal ileum and colon Producing enterotoxin (Shiga toxin)
34
How should shigella infection be managed?
Avoid antibiotics If really necessary, go for ciprofloxacin self limiting 7 days
35
What is the typical stool appearance in Vibrio cholerae infection?
massive diarrhoea (rice water stool) without inflammatory cells
36
Which organism is most likely to cause cellulitis in a scuba diver/shellfish handler?
Vibrio vulnificus
37
On what sort of agar can vibrio spp be grown?
Salty agar
38
For how long can campylobacter symptoms last?
Up to 20 days only treat if immunocompromised - erythromycin or cipro if in the first 4-5days
39
What is one key serious complication of campylobacter infection?
Guillan Barre syndrome Reactive arthritis Reiter's syndrome
40
What is the symptom of "flask-shaped ulcer" pathognemonic for?
Entamoeba histolytica Ingestion of cysts: trophos in ileum → colonize cecum and colon → “flask shaped” ulcer
41
What symptoms does E. histolytica infection cause?
Dysentry and flatulence Tenesmus chronic form: weight loss +/- diarrhoea, liver abscess
42
How should E. histolytica infection be managed?
metronidazole and paromomycin in luminal disease
43
Describe the microbiology of giardia lamblia
Trophozoite “pear shaped”; 2 nuclei 4 flagella and a suction disk
44
How can giardia infection be investigated?
String test stool micro, ELISA, “string test”
45
How should giardia infection be treated?
Metronidazole
46
In which patient group does cryptosporum parvum cause symptoms, and what are those symptoms?
The immunocompromised Severe diarrhoea
47
Recall the 1st and 2nd line treatments for clostridium difficile
1. Metronidazole 2. Vancomycin
48
define gastroenteritis
rapid onset diarrhoea, lasting \<2 weeks with diarrhoea ≥3/day or ≥200g of stool which is either viral or bacterial in aetiology
49
define diarrhoea
loose or watery stool, ≥3 times in 24 hours, acute/chronic/persistent
50
How would you classify acute/persistent/chronic diarrhoea?
**acute**: \<14 days (viral/bacterial) **persistent**: 14-29 days **chronic**: \>30 days
51
How do large and small bowel diarrhoea difer?
Small bowel diarrhoea = watery, crampy abdominal pain, bloating and gas; inflammatory cells rare Large bowel diarrhoea = small volume, painful, occur with blood/mucous; inflammatory cells common
52
WHat are the reportable organisms for gastroenteritis?
Campylobacter, Salmonella, Shigella, E. coli 0157, Listeria, Norovirus
53
Which gastroenteric organisms may cause aortitis, osteomyelitis, deep tissue infection?
salmonella yersinia
54
Which gastroenteric organisms may cause haemolytic anaemia
Campylobacteria Yersinia
55
Which gastroenteric organisms may cause glomerulonephritis?
Shigella, Campylobacter, Yersinia
56
Which gastroenteric organisms may cause HUS?
STEC, Shigella
57
Which gastroenteric organisms may cause erythema nodosum?
Yersinia, Campylobacter, Salmonella, Shigella
58
Which gastroenteric organisms may cause reactive arthritis?
Salmonella, Shigella, Campylobacter, Yersinia, (giardia, Cyclospora cayetanensis)
59
Which gastroenteric organisms may cause meningitis?
Listeria, salmonella (infants \<3m)
60
Recall 3 gram positive rods causing gastroenteritis
BAcillus cereus Clostridia Listeria monocytogenes
61
Recall the different types of E coli
ETEC - toxigenic (main cause of traveller’s diarrhoea) EPEC - pathogenic (infantile diarrhoea) EIEC - invasive - dysentery EHEC - haemorrhagic also called shiga toxin producing EC (STEC) O157:H7 EHEC: - shiga like verocytotoxin -\> HUS
62
Which bacteria multiples in Peyer's patches?
S typhi
63
which abx is used for S typhi?
ceftriaxone
64
Which bacteria is curved, comma shaped, late lactose fermenters, oxidase positive
vibrio
65
REcall 3 gram negative rods causing gastroenteritis
Enterobacteriaceae Vibrio Campylobacter
66
How to treat Vibrio cholerae
Treat the losses: electrolyte replacement and fluids
67
What are the signs and symptoms of campylobacter?
Watery, foul smelling diarrhoea, bloody stool, fever and severe abdominal pain
68
What are the s/s of Giardia?
foul smelling non-bloody diarrhoea, cramps, flatulence, no fever
69
How to diagnose cryptosporum parvum ?
Oocysts seen in stool by modified Kinyoun acid fast stain
70
Which gastroenteritis virus is most associated with outbreaks?
norovirus
71
which virus appears 'wheel like' and causes gastroenteritis?
rotavirus exposure to natural infection twice confers lifelong immunity
72
which gastroenteritic organisms are notifiable to PHE?
Campylobacter, Clostridium species, Listeria monocytogenes, Vibrio, Yersinia

Pathology ICSM COPY (90 decks)

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