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Study Notes - Gastroenterology > Microbiology 1 (Dr Orange) > Flashcards

Microbiology 1 (Dr Orange) Flashcards

(90 cards)

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1
Q

What host factors affect your risk of gastrointestinal infection? (5)

A 
Age (very young and elderly)
Decreased gastric acid secretion
Decreased gut motility
Influence of colonic microflora
Intestinal immunity
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2
Q

What bacterias seen in the UK cause Gastrointestinal infections? (8)

A 
Campylobacter coli/ jejuni
Salmonella enterica
E coli O157
Shigella sonnei
Staph aureus/ Clostridium perfingens/ Bacillus cereus
C difficile
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3
Q

What viruses seen in the UK cause gastrointestinal infections? (2)

A

Norovirus

Rotavirus

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4
Q

What parasites seen in the UK cause gastrointestinal infections? (2)

A

Cryptosporidium sp

Giardia lamblia

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5
Q

What bacterias, usually imported from abroad, case gastrointestinal infections?

A

Vibrio cholerae/ parahaemolyticus
Salmonella typhi/ paratyphi
Aeromonas sp.
Shigella dysenteriae/ flexneri/ boydii

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6
Q

What parasite, usually imported from abroad, can cause GI infections?

A

Entamoeba histolytica

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7
Q

What is diarrhoea?

A

3 or more loose stools in 24 hours

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8
Q

What is the source/ reservoir of infection?

A

The original source of the infection e.g. animal gut, another human’s gut, etc.

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9
Q

What is the vehicle of infection?

A

The means by which the infection is transmitted from one person to another (e.g. contaminated food/ water)

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10
Q

What is the source and vehicle of infection of E. coli O157

A

Source = cattle GI tract

Vehicle of infection = undercooked hamburger

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11
Q

What shape is camplobacter (C. jejune, C. coli)?

A

Curved gram negative bacilus

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12
Q

What is the commonest cause bacterial GI infection in the UK?

A

Campylobacter

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13
Q

Incubation period of campylobacter?

A

3-10 days

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14
Q

How does campylobacter make you unwell?

A

Causes inflammation of the colon and rectum leading to bloody diarrhoea
Can invade and occasionally get into bloodstream (patients get systemically unwell with flu like symptoms)

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15
Q

What is the main source/ vehicle of infection of campylobacter?

A

Undercooked poultry + other farm animals, water and unpasteurised milk (person to person spread is rare - outbreaks usually because consumed the same chicken)

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16
Q

Symptoms of campylobacter?

A

Abdo pain

Diarrhoea =/- blood

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17
Q

Management of campylobacter?

A

Usually self limiting but give ERYTHROMYCIN or CIPROFLOXACIN for 5 days if patient develops systemic illness

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18
Q

What does “enteric” in Salmonella enterica mean?

A

It is the agreed species name for all food poisoning i.e. non-typhoidal salmonella (often still called by species name e.g. S. enteritiditis, S. typhimurium, etc.

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19
Q

What is the incubation period for Salmonella enterica?

A

12 - 48 hours

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20
Q

What is the mechanism of action of Salmonella enterica?

A

Causes inflammation of the ileum and colon - multiply in gut and cause mucosal damage, decreased mucosal damage and increased fluid excretion
Can invade and occasionally get into bloodstream

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21
Q

What is the source/ vehicle of infection of salmonella enterica?

A

Undercooked poultry + other farm animals (much less common since immunisation of poultry against Salmonella spp.)

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22
Q

Symptoms of salmonella enterica?

A

Abdo pain
Diarrhoea (occasionally bloody)
Vomiting

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23
Q

Management of salmonella?

A

Usually ciprofloxacin for 5 days if patient at risk of or develops systemic illness

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24
Q

What type of Shigella is seen in the UK?

A

Shigella sonnei (most benign type) - outbreaks occur every few years amongst cohorts of vulnerable children

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25
Incubation period for Shigella sonnei?
1-9 days
26
Mechanism of action of Shigella sonnei?
Invades intestinal mucosa causing severe inflammation, but does not invade further (never seen in blood cultures)
27
What is seen in the stools of a patient with Shigella?
Blood and pus cells
28
Source/ vehicle of infection of Shigella?
Human only infection | Often spread person- person amongst young children in schools, etc.
29
Symptoms of shigella Sonnei?
Abdo pain | Diarrhoea (occasionally blood)
30
Management of Shigella sonnei?
Usually self-limiting - symptomatic treatment only Other species of Shigella (dysenteriae, etc.) acquired abroad, usually require Ciprofloxacin due to more severe infection
31
What strain of E coli produces a toxin that damages red blood cells and the kidneys?
The O157:H7 strain (and a few other serotypes)
32
What type of toxin does E coli O157 produce and what does this do?
verotoxin (VTEC) Damages red cells and the kidney, causing haemolytic-uraemic syndrome (HUS) (increased blood urea, red cell haemolysis and thrombocytopenia)
33
Who are most at risk of developing HUS?
Children
34
What is the source/ vehicle of infection of E coli O157?
Carried as part of the normal gut flora in cattle Beef becomes contained on the outside at slaughter = increased risk from minced meat and hamburgers than from a steak Nursery/ school visits to farm Private (untreated) water supplies = run off water from fields Low infecting dose, so person-person spread causes 2y cases
35
Symptoms of E coli O157?
Abdo pain | Bloody diarrhoea is common
36
Management of E coli O157?
Symptomatic and supportive treatment only Antibiotics contraindicated as may increase release of toxin Check bloods for HUS 1 week after onset of symptoms
37
What does verotoxin do?
Binds to receptors found on renal cells, RBC and others Inhibits protein synthesis Causes cell death
38
Clinical presentation of HUS?
``` Abdo pain Fever Pallor Petechiae Oliguria (decreased urine production) Bloody diarrhoea in 90% of cases Mostly in under 16s ```
39
When is the peak presentation of HYS?
7-10 days after onset of diarrhoea
40
What does blood tests show which indicates HUS? (5)
``` High white cells Low platelets Low Hb Red cell fragments Lactate dehydrogenase (increased 1.5 times normal) ```
41
Appearance of Salmonella, Shigella and E coli O157 on gram film? What is used to differentiate between these?
Gram negative bacilli | Biochemical tests, then serological tests
42
What bacteria causes typhoid and paratyphoid fever?
Salmonella typhi/ salmonella paratyphi A and B
43
What are the symptoms of typhoid/ paratyphoid fever?
Initially a febrile illness (bacteria circulating in bloodstream) causing headache, flu-like symptoms followed by diarrhoea 2 weeks later
44
When is typhoid/ paratyphoid seen in the UK?
When it has been imported from abroad
45
Incubation period of typhoid/ paratyphoid fever?
14 - 21 days
46
Mechanism of action of typhoid/ paratyphoid?
Organism invades from gut lame -> lymphatic system -> bloodstream -> reticuloendothelial system and gall bladder -> gut lumen and invades Peyer's patches
47
In chronic carriers of typhoid/ parathyroid, where does the bacteria reside?
The gallbladder
48
What can happen during the bacteraemic phase of typhoid/ paratyphoid?
Distant sites can become infected e.g. ostemyelitis
49
Source of salmonella typhi/ paratyphi?
Human only infection Spread person-person or from drinking contaminated water/ eating contaminated food/ poor sanitation (different from entericas which are associated with animals)
50
Symptoms of typhoid/ paratyphoid?
Fever Rash on abdomen ("rose spots") Diarrhoea
51
Management of Typhoid/ paratyphoid?
Antibiotics are required, choice depends on sensitivities. Resistance to ciprofloxacin
52
What causes cholera?
Vibrio cholerae ("the comma bacillus")
53
What is the appearance of Vibrio cholera?
Small curved gram negative baciluus
54
Where are outbreaks of cholera common?
In disaster/ war stricken situations
55
Incubation period of cholera?
1-9 days
56
Mechanism of action of cholera?
Organism produces an exotoxin that causes active outpouring of fluid from cells of small intestine resulting in severe watery diarrhoea
57
Source/ vehicle of infection of Vibrio cholerae
Human only infection - spread person-person or from drinking contaminated water/ poor sanitation
58
Symptoms of cholera?
Watery diarrhoea "rice water stools" causing rapid dehydration
59
Management of cholera?
Fluid and electrolyte replacement | Antibiotics NOT indicated
60
What causes GI infections associated with ingestion of pre-formed toxin? (3)
Staph aureus Clostridium perfingens Bacillus cereus
61
What is an enterotoxin?
A protein exotoxin released that targets the intestine
62
What is the typical scenario where Staph aureus is passed on through food?
Bakery worker with infected finger touches cream cake Staph aureus multiplies producing enterotoxin (exotoxin) Customer ingests enterotoxin
63
What does ingestion of staph aureus enterotoxin cause?
Acts directly on vagus nerve and vomiting centre inducing vomiting within 1 - 2 hours
64
What is the appearance of clostridium perfingens?
Large gram positive anaerobic bacillus
65
Where is clostridium profanens normally found?
Part of the normal gut flora in humans and animals
66
How does clostridium perfringens cause infection?
Spores survive cooking, then turn into vegetative organism some strains of which produce enterotoxin (an exotoxin)
67
What is clostridium perfringens infection associated with?
Inadequately refrigerated re-heated meat gravy
68
What is the appearance of bacillus cereus?
Large gram positive aerobic bacillus
69
How can a patient contract bacillus cereus?
Exotoxin can be ingested as pre-formed toxin in food Organism can multiply in intestine, producing toxin that is absorbed from the gut Spores survive cooking, then turn into vegetative organisms that produce toxin
70
What is bacillus cereus infection associated with?
Contaminated inadequately refrigerated reheated rice
71
What 2 bacterias have short incubation periods? (1-6 hours)
Staph aureus
72
What 2 bacterias have a medium incubation period? (12-48hours)?
Salmonella | Cl perfrigens
73
What 2 bacteria have a long incubation period? (2-14 days)
Campylobacter | E coli O157
74
Cryptosporidium and Giardia lamblia are both protozoal infections - true/ false?
True
75
Mechanism of action of cryptosporidium?
Infection occurs when cysts are ingested which "hatch" into trophozoites that invade the cells of the small intestine
76
Source/ vehicle of infection of cryptosporidium?
Domestic animals, especially calves Person-person spread Outbreaks associated with contaminated water supplies and swimming pools (cysts resistant to chlorine)
77
Symptoms of cryptosporidium?
Diarrhoea | Particularly severe in HIV pos patients
78
Management of Cryptosporidium?
Symptomatic treatment only
79
What type of stain can be used to identify cryptosporidium cysts?
Ziehl-Neelson stain (pink cysts against blue background)
80
Mechanism of action of Giardia lamblia?
Infection occurs when cysts are ingested which "hatch" into trophozoites that invade the cells of the upper small intestine
81
Source/ vehicle of infection of Giardia lamblia?
Human only infection ?person to person spread Outbreaks associated with contaminated water supplies
82
Symptoms of Giardia lamblia?
``` Diarrhoea Malabsorption syndrome Anorexia Abdominal pain Flatulence ```
83
Management of Giardia lamblia?
Oral metronidazole
84
What is the more commonly used name for Enterobius vermicularis?
Threadworms
85
Pathogenesis of thread worms?
Ova (egg) ingested -> hatch in intestine and live in caecum and colon -> adult females come out on to perianal skin at night and lay ova -> ova cause perianal itch -> child scratches bottom -> puts fingers in mouth
86
Source/ vehicle of transport of enterobius vermicularis?
Human only infection | Person-person spread (poor hygiene)
87
Symptoms of Enterobius vermicularis?
Perianal itch | Worms seen in stool
88
What is the treatment for Enterobius vermicularis?
Oral mebendazole (often have to treat all members of family at once)
89
What must be done if blood is seen in the patients stool?
Stool must be sent to ref lab for E coli verotoxin detection
90
When sending a stool sample to the lab for testing, what must you tell the lab if the patient has been abroad?
Where they were

Study Notes - Gastroenterology (42 decks)

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