Clinical Microbiology > Gastrointestinal Tract Infections > Flashcards

Gastrointestinal Tract Infections Flashcards

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1
Q

What are the host defence mechanisms of the GI tract?

A

Stomach acid
Bile salts
Mucosal Defences

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2
Q

What pH should stomach acid be?

A

4

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3
Q

What are the 3 parts of the mucosal defences?

A

IgA
Phagocytes
Digestive enzymes

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4
Q

What does gut motility do?

A

Peristalsis impedes attachment

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5
Q

What does commensal flora mean?

A

Microorganisms, such as bacteria, that live on or inside a host without causing harm, and are often beneficial by providing protection from pathogens

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6
Q

How does commensal flora help defend the GI tract?

A

Confers colonisation resistance
Competition
Enterobacteriaceae produce bacteriocin
Changes to local pH
Production of H2S and fatty acids

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7
Q

Are small intestine commensal flora mostly gram negative or positive?

A

Gram Positive

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8
Q

What is infective gastroenteritis characterised by?

A

Inflammation
Diarrhea
Vomiting
Abdominal pain

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9
Q

What is bacterial food poisoning also known as?

A

Acute gastroenteritis

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10
Q

What are the most common bacterial strains associated with gastroenteritis?

A

Salmonella
Shigella
E. Coli
Bacillus Cereus

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11
Q

What causes gastroenteritis outbreaks?

A

Ingestion of contaminated food or water
Recreational contact with contaminated water
Direct contact with animals

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12
Q

What should be noted in stool culture samples?

A

Blood
Mucous
Parasites

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13
Q

Should a gram stain be performed on a stool sample?

A

No

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14
Q

What culture should be used for stool sample analysis?

A

Selective media
Differential media

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15
Q

What is dysentry?

A

Inflammatory disorder of lower GIT
Severe diarrhoea with blood and mucus in the faeces

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16
Q

What agar should be used to detect lactose fermenters?

A

MacConkey

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17
Q

What agar should be used to detect non-lactose fermenters?

A

MacConkey

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18
Q

What is an example of a lactose fermenter?

A

E. Coli

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19
Q

What is an example of a non-lactose fermenter?

A

Salmonella
Shigella

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20
Q

How does salmonella appear on DCA?

A

Small black colonies

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21
Q

How does shigella appear on DCA?

A

Colourless colonies

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22
Q

How does salmonella appear on XLD?

A

Red colonies with black centres

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23
Q

Why does salmonella have a dark centre on DCA and XLD plates?

A

Hydrogen sulphide production

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24
Q

How does E. Coli appear on XLD?

A

Yellow colonies

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25
What is the characterised shape of Campylobacter cells?
S-shaped
26
What disease is Campylobacter the leading cause of?
Enteritis
27
What can appear in faeces to indicate Campylobacter infection?
Blood Mucuos
28
What is the gram reaction of Campylobacter?
Negative
29
What is bacteraemia?
Presence of bacteria in the bloodstream
30
What type of agar is used to confirm Campylobacter presence?
Charcoal Cefperazone Desoxycholate agar (CCDA)
31
How do colonies of Campylobacter appear on CCDA?
Grey Moist Metallic Sheen
32
Is Campylobacter oxidase positive or negative?
Positive
33
What disease is commonly caused by Salmonella Enterica?
Gastroenteritis
34
What type of salmonella serotypes cause serious systemic infections?
Typhi Paratyphi
35
What bacterial family is salmonella a member of?
Enterobacteriaceae
36
Is Salmonella aerobic or anaerobic?
Facultatively anaerobic
37
What is the gram reaction of salmonella?
Negative
38
What are the 3 key antigens of Salmonella?
H O Vi
39
What type of antigen is H?
Diphasic flagella (motile)
40
What does motile mean?
Capable of motion
41
What is the O antigen?
Lipopolysaccharide
42
What is the Vi antigen?
Polysaccharide of S. Typhi
43
Is the Vi antigen virulent?
Yes
44
What does virulent mean?
Hostile
45
How was Salmonella originally typed?
Kauffmann-White scheme
46
What type of salmonella causes gastroenteritis?
Non-typhoid Salmonella
47
How can a patient acquire gastroenteritis?
Contaminated water Contact with infected people Foreign travel
48
Can gastroenteritis be asymptomatic?
Yes
49
How can gastroenteritis present?
Bacteraemia
50
What agar(s) can be used to identify Salmonella?
XLD DCA Chromogenic
51
Is it always required to culture salmonella?
No
52
What enrichment broths should be used to culture Salmonella if necessary?
Selenite cysteine Rappaport Vassiliadis
53
What is the biochemical profile of Salmonella?
Lactose negative Oxidase negative Hydrogen sulphide producer
54
What other test can be used to help identify Salmonella species?
API 20E
55
What does MALDI-TOF do?
Rapidly identify bacteria
56
What does MALDI-TOF use from the bacteria to compare it to the database?
It's "molecular fingerprint"
57
What is the first step in confirming salmonella infection?
O somatic and H flagella antigens used to type salmonella -serovars
58
What is the second step in confirming salmonella infection?
Polyvalent O antigens first used
59
What is the third step in confirming salmonella infection?
If agglutinates with polyvalent use individual antisera
60
What is the fourth step in confirming salmonella infection?
Repeat with H antisera
61
What are the benefits of whole genome sequencing?
Overcoming the variability in antibody preparations Removing the need to use laboratory animals Implementing a truly universal system
62
What is salmonella enteric (typhoid) fever caused by?
S. Typhi (typhoid) S. Paratyphi A, B or C (paratyphoid)
63
If a patient presents with suspected salmonella enteric fever what level of containment are the samples used at?
3
64
If a patient is suspected to have typhoid, what culture(s) should be undergone?
Blood cultures Bile Bone marrow Urine
65
What can individuals of a salmonella enteric fever become?
Chronic carriers of the disease
66
What family is shigellae apart of?
Enterobacteriaceae
67
What is the gram reaction of shigellae?
Negative
68
Are shigellae anaerobic or aerobic?
Facultatively anaerobic
69
What are other key biochemical properties of shigellae?
Non-motile Non-encapsulated No fimbriae
70
What is the key antigen of shigellae?
O antigen (Lipopolysaccharide)
71
What type of shigella dysenteriae cause the most severe type of the disease?
Type 1
72
What is the toxin that causes damage during shigella infection?
Cytotoxin (Shiga toxin)
73
What does shiga toxin do?
Destroys epithelial cells causing inflammatory diarrhoea and dysentery
74
What agar type(s) should shigella diagnosis occur on?
XLD DCA
75
How does shigella present on DCA?
Small pink colonies
76
What gram reaction does E. coli present?
Negative
77
Is E. Coli aerobic or anaerobic?
Facultatively anaerobic
78
What agar type(s) should be used to identify E. Coli?
CLED DCA Mac
79
Are E. Coli motile?
Yes
80
Is E. Coli a lactose or non-lactose fermenter?
Lactose fermenter
81
What does E. Coli produce from fermenting lactose?
Acid Gas
82
How does E. Coli present on CLED?
Yellow colonies
83
How does E. Coli present on MAC?
Pink/ Red colonies
84
How does E. Coli present on DCA?
Pink colonies
85
What do some E. Coli strains produce?
Shiga toxin (won't appear the same on the agar plates)
86
What can E. Coli also produce?
Indole
87
What is a toxin similar to shiga toxin that is associated with E. Coli?
Verocytotoxin
88
What occurs in a patient suffering from Haemolytic Uremic Syndrome?
Toxins damage the lining of the large intestine Abnormal premature destruction of red blood cells Damaged red blood cells clog the filtering system in the kidneys Extreme complications (e.g. stroke)
89
What are examples of treatment for gastrointestinal infections?
Drinking sufficient fluids Pain relief for abdominal cramps Antibiotics
Clinical Microbiology
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