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Microbiology > GI Infections > Flashcards

GI Infections Flashcards

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1
Q

What is the concern in developing countries?

A

Outbreaks such as cholera.
No access to clean drinking water and sanitation
Most vulnerable children and elderly

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2
Q

What are the reportable infections?

A

Campylobacter, salmonella, shigella, E. coli 0157, listeria, norovirus

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3
Q

What age group tend to be the most infected but not the most vulnerable?

A

15-45

Self limiting

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4
Q

What is the first clinical syndrome?

A

No fever, low grade, no WBC in stool.
Cholerae, ETEC, EAggEC, EPEC, EHEC.
Secretory diarrhoea

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5
Q

What is the second clinical syndrome?

A

Fever, WBC in stool
Campylobacter, shigella, non typhoid all salmonella, EIEC
Inflammatory diarrhoea

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6
Q

What is the 3rd clinical syndrome?

A

Fever, WBC in stool (mononuclear)
Typhoidal salmonella, enteropathogenic yersinia, brucella
Enteric fever

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7
Q

Incubation and duration for campylobacter?

A

1-10 days incubation
2-20 days duration
Poultry

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8
Q

Incubation and duration for E. coli?

A

1-5 days incubation
1-4 days duration
HUS, verotoxin

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9
Q

Incubation and duration for shigella?

A

12-96 hours incubation
5-7 days duration
Small infective dose, outbreaks

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10
Q

Incubation and duration for non typhoidal salmonella?

A

8-48 hours incubation
4-7 days duration
Rare cause of systemic disease

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11
Q

Incubation and duration for vibrio parahaemolyticus?

A

24-72 hours incubation
2-10 days
Shellfish

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12
Q

Incubation and duration for cholera?

A

1-5 days incubation
Variable duration
Ricewater, endemic

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13
Q

Incubation and duration for b cereus?

A

1-6 hours incubation
Less than1 day duration
Heat stable emetic toxin (rice)

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14
Q

Incubation and duration for staph aureus?

A

2-7 hours duration
Less than one day duration
Preformed toxin

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15
Q

Mechanism for cholera- secretory diarrhoea

A

Toxins bind to units
Opening up of chloride channels at the apical membrane of enterocytes by cAMP
Effluent of chloride into the lumen with loss of water and electrolytes

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16
Q

Mechanism of disease with secretory diarrhoea- super antigen

A

Antigen binds to T cell receptors and MHC molecules
Outside the peptide binding site
Massive cytokine production by CD4 cells ie systemic toxicity and suppression of adaptive response

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17
Q

Who tends to get an exudative or inflammatory response?

A

Immunocompromised patients

Septic shock

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18
Q

What happens with interstitial inflammation/enteric?

A

Immunocompetent, no septic shock.

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19
Q

Facts about s aureus leading to food poisoning?

A

1/3 chronic carriers, 1/3 transient
Spread by skin lesion on food handlers
Catalase, coagulase, gram positive coccus
Appears in tetrads, clusters on gram stain
Yellow colonies

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20
Q

What is the mechanism of s aureus?

A

Produces an enterotoxin, an exotoxin that can act as a super antigen, releasing IL 1 and 2.
Causing prominent vomiting and watery non bloody diarrhoea
Self limiting
No heat inactivation

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21
Q

Mechanism for b cereus?

A 
Gram positive rod, spore forming 
Spores germinate in reheated fried rice 
Heat stable emetic toxin 
Heat labile diarrhoeal toxin 
Watery non bloody diarrhoea 
Self limited 
Rare cause of bacteraemia
Can cause cerebral abcess
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22
Q

Facts about clostridium botulinum?

A

Gram positive anaerobes
Source is canned or vacuumed food
Ingestion of preformed toxin, inactivated by Heat
Blocks ACH release from peripheral nerve synapses
Tx is with antitoxin

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23
Q

Mechanism for clostridium pefringens?

A 
Reheated food/meat
Affects normal flora of colon but not small bowel, where super antigen acts 
8-16 hours incubation
Watery diarrhoea 
Cramps
Vomiting 24 hours
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24
Q

C diff?

A

Pseudo membranous colitis
3% population 30% hospital
Abx related colitis mainly, cephalosporin, Citroen and clindamycin
Monitor albumin, renal function and white cells
Tx with oral metro, vanco.

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25
Q

Listeria monocytogenes?

A

Outbreaks of febrile gastroenteritis
Pregnant ladies, perinatal infection
B haemolytic, aesculin positive with tumbling motility
Refridgerated food, grows at 4 degrees Celsius
Watery diarrhoea, cramps, headache, fever, little vomiting
Tx with ampicillin, ceftriaxone, cotrimoxazole

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26
Q

What are enterobacteriae?

A

Facultative anaerobes, glucose/lactose fermenters, oxidase negative

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27
Q

E. coli?

A

Travellers diarrhoea
Food/water contaminated with human faeces
Enterotoxins- Heat labile stimulates adenyl cyclase, and cAMP
Heat stable stimulates guanylate cyclase
Act on jejenun and ileum NOT colon

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28
Q

What is ETEC?

A

Toxigenic

Travellers diarrhoea

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29
Q

What is EPEC?

A

Pathogenic

Infantile diarrhoea

30
Q

What is EIEC?

A

Invasive

Dysentry

31
Q

What is EHEC?

A

Haemorrhagic O157
Shiga like verocytotoxin causes HUS
Avoid abx

32
Q

Why are infections underreported?

A

Most are self limiting, under 24 hours, patients do not seek healthcare

33
Q

What are salmonellae?

A

They are non lactose fermenters, they produce hydrogen disulphide
They produce antigens

34
Q

What are the antigens from salmonellae?

A

Cell wall O(groups a-I)
Flagellar H
Capsular Vi (virulence and antiphagocytic)

35
Q

What are the 3 salmonellae species?

A

S typhi
S enteritidis
S cholerasuis

36
Q

What does s enteritidis cause?

A 
Enterocolitis, poultry, eggs, meat
Invasion of epi and sub epithelial tissue of small and large bowel 
Bacteraemia is infrequent 
Self limited, non bloody diarrhoea 
Give cipro after 3-5 days 
Stool positivity
37
Q

What does s typhi cause?

A 
Enteric fever, South East Asia, humans 
Multiples in payers patches 
Often bacteriaemic
Slow, fever, constipation 
Splenomegaly 
Rose spots
Anaemia, leucopenia, bradycardia, haemorrhage
Blood culture positive (abcess.mycotic aneurysm)
Treat with ceftriaxone
38
Q

What is shigellae?

A

Gram negative anaerobes, non motile

39
Q

What are the shigellae antigens?

A

Cell wall O

Polysaccharide groups a-d

40
Q

What are the 3 shigellae species?

A

S sonnei, s dysenteriae, s flexneri (msm, faecal)
The most effective enteric pathogen low ID 50
No animal reservoir
No carrier state

41
Q

What does shigella cause?

A 
Dysentery, invading cells of mucosa of distal ileum and colon
Producing enterotoxin (shigatoxin) 
Avoid abx (ciprofloxacin to prevent onward spread)
42
Q

What are vibrios?

A

Gram negative rod shaped, late lactose fermenters, oxidase positive

43
Q

What is vibrio cholera?

A

O1 group causes epidemics
Non O1 group is sporadic or non pathogens
Transmitted by contamination of water and food from human faeces (shellfish, oysters and shrimp)

44
Q

How does v cholera work?

A

Colonisation of the small bowel, secretion of enterotoxin with A and B subunit, causing persistent stimulation of adenylate cyclise
Massive diarrhoea without any white cells

45
Q

How does vibrio parahaemolyticus work?

A

Ingestion of raw or undercooked seafood
Major cause of diarrhoea in Japan, or cruising
Self limiting for 3 days
Grows in salty conditions

46
Q

How does vibrio vulnificus work?

A

Causes cellulitis in shellfish handlers, waterborne.
Can cause fatal septicaemia if immunosuppressive (HIV)
Treat with doxycycline

47
Q

What is campylobacter?

A

Gram negative, microaerophilic
Grows at 42 degrees
Motile, oxidative positive
Self limiting but symptoms can last for 20 days
Lives in poultry gut
Only treat with immunocomprimise does with macrolide

48
Q

How is campylobacter transmitted?

A

Contaminated food and water with animal faeces (poultry, meat, birds pecking on milk)
Enterotoxin, watery diarrhoea
Fever, abdo pain
Not sure if it invades blood (f one does)
Treat with erythromycin or cipro in first 4-5days

49
Q

What syndrome can campylobacter cause?

A

GBS
Reactive arthritis
Reiters disease

50
Q

What is yersinia enterocolitica?

A

Gram negative rod shaped
Non lactose fermenters, prefers cold 4 degrees
Transmitted via food contaminated with domestic animal poo
Can cause enterocolitis, mesenteric adenitis, assoc reactive arthritis, reiters

51
Q

What is entamoeba histolytica?

A 
Protozoa
Motile trophozoite in diarrhoea 
Non motile in non diarrhoeal 
Killed by boiling, removed by water filter 
4 nuclei, no animal reservoir
52
Q

How does e histolytica work?

A 
Ingestion of cysts, trophies in ileum, colonise caecum, causes flask shaped ulcer 
Dysentery and flatulence 
Tenesmus 
Chronic weight loss, plus diarrhoea 
Liver abscess
53
Q

How would you diagnose e histolytica?

A 
Stool microbiology (wet mount, iodine, trichrome) 
Serology in invasive disease
54
Q

How do you treat e histolytica?

A

Metro plus paromomycin in luminal disease

55
Q

What is giardia?

A

Protozoa, trophozoite
Pear shaped
2 nuclei, 4 flagella, suction disk

56
Q

How is giardia passed?

A

Ingestion of cyst from faecally contaminate water, food
Excystation at the duodenum
Tropho attaches
No invasion but malabsorption of protein or fat
Travellers hikers, day care, mental hospital people can’t look after themselves msm.

57
Q

What are the symptoms of giardia?

A

Foul smelling non bloody diarrhoea stool floats
Cramps
Flatulence
No fever

58
Q

How can you diagnose giardia?

A

Stool microscopy
ELISA
String test- capsule with string into stomach
Treat with metro

59
Q

What is cryptosporidium parvum?

A

Protozoa, infects the jejenum
Severe diarrhoea in the immunocompromised
Oocysts seen in stool, modified by kinyoun acid fast stain
Treatment- reconstitution of immune system
Picked up from swimming

60
Q

What is norovirus?

A 
Causes outbreaks
Low ID (18-1000 viral particles) 
Resilient up to 60 degrees celcius 
No long term immunity 
G2.4 is the currently predominant strain 
Vomiting and diarrhoea
61
Q

What is rotavirus?

A 
Wheel like virus, dsRNA
Replicates in mucosa of small intestine
Secretory diarrhoea 
No inflammation 
Can get watery diarrhoea by stimulation of enteric nervous system
62
Q

Who gets rotavirus?

A

Age 6 kids most have it

Exposure to natural infection twice confers lifelong immunity

63
Q

What can adenovirus cause?

A

Types 40, 41 cause non bloody diarrhoea, usually less than 2 years of age
Any type in immunocompromised

64
Q

How do you diagnose adenovirus?

A

Stool em, antigen detection, PCR

65
Q

What are the targets for prevention promotion?

A

Breast feeding, improved weening practice
Clean water for drinking
Safe disposal of stools of young children
Precautions when travelling
Food handling
Public health notification
Good handwashing

66
Q

What is the cholera vaccine?

A

Inactivated whole cell, contains serogroups O1 and O139
Plus beta unit of toxin
Live is not recommend

67
Q

What about campylobacter vaccine?

A

One available for military, infant and travellers

Candidate vaccines exist only for high risk

68
Q

Are there any ETEC vaccines?

A

Inactivated and live vaccines in trials

69
Q

Is there a salmonella vaccine?

A

Yes, vi capsular ps (IM) and oral live

70
Q

What are the rotavirus vaccines?

A

Rotarix- live attenuated human strain, 2 oral doses
Rotateq- pentavalent, 3 oral doses, one bovine, 4 human strains
6-12 weeks , UK don’t get it really

71
Q

What are the notifiable diseases?

A

Camp, clostridium, listeria, vibrio, yersinia, shigella, salmonella?
Identify outbreaks in areas

Microbiology (15 decks)

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