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Clinical Micro > Lecture 3 URTI > Flashcards

Lecture 3 URTI Flashcards

1
Q

What is the most common cause of step throat

A

Group A Strep

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2
Q

The LRT has a normal flora, true or false?

A

False. LRT does not have a normal flora ‘sterile site’ but the URT does.

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3
Q

What part of the respiratory tract helps keeps us uninfected.

A

Mucus and mucociliary tract

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4
Q

What is the role of the epiglottis

A

Stop food going into the lungs

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5
Q

What is inflammation of the pharynx called?

A

Pharyngitis (sore throat)

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6
Q

What microorganisms commonly cause acute epiglottitis

A

Haemophilus influenzae capsular type B common cause of epiglottis especially in children

H. Influenzae is part of normal flora! Friend vs foe

Also group A beta haemolytic streptococci become more frequent after widespread use of h. Influenzae vaccine.

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7
Q

Name 3 microorganisms that are ‘common residents’ of the URT

A

Viridians streptococci
C albicans (mouth)
Haemophilus influenzae

Another example is anaerobic microorganisms (e.g.. bacteroides deep within the gum)

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8
Q

Name 2 microorganisms that are ‘occasional residents’ of the URT

A

Streptococcus pyogenes
Streptococcus pneumoniae

(TRUE PATHOGENS - CARRY FOR SOME TIME THEN PASS ON TO SOMEONE ELSE)

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9
Q

Which microorganisms are associated with colonisation and ‘superinfection’ following antibiotic treatment?

A

1- coliforms (e. Coli)
2- pseudomonas spp.
3- candida albicans (oral thrush)

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10
Q

Name 3 microorganisms of URT that can be used as part of friend vs foe argument

A

Candida albicans
Haemophilus influenzae
Streptococcus mutans (normally colonise mouth)

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11
Q

What dental disease can S. mutans cause and why

A

Dental caries when teeth aren’t brushed properly so s mutans can adhere to enamel and cause biofilms.

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12
Q

What percentage of people are the following ‘residents’ present in:
1- common residents
2- occasional residents
3- organisms associated with colonisation and superinfection following antibiotic treatment

A

1- >50% of people
2- <10%
3- less than 1%

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13
Q

State the difference between primary and secondary invaders of URT

A

Primary = successfully infect the healthy respiratory tract; possess mechanism to attach and spread - true pathogens

Secondary = cause disease when host defences are impaired e.g. Normal flora c albicans or primary invaders s. Pneumoniae

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14
Q

Briefly describe how primary invaders are capable of causing disease

A

(a) adhesion to normal mucosa (in spite of mucociliary system) e.g surface proteins, capsid proteins
(b) avoid host defence e.g. Capsule
(c) ability to damage local tissue (exotoxins/enzymes e.g. Pneumolysin)

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15
Q

Approximately how many different antigenic types are there of rhinovirus

A

100

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16
Q

What 4 proteins make up the viral capsid that encases the RNA genome

A

VP1, VP2, VP3, VP4

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17
Q

What is the role of VP1, VP2 AND VP3 proteins in rhinovirus function

A

They account for virus antigenic diversity

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18
Q

What is the role of VP4 in rhinovirus function

A

Anchors the RNA core to the capsid.

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19
Q

A canyon in which of the proteins of rhinovirus serves as the site of attachment for cell surface receptors

A

VP1.

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20
Q

What percentage of HRV serotypes utilise the cell surface receptor ICAM1, and what is the other cell surface receptor used by the ‘minor group’

A

90% use ICAM-1

Minor group attaches to an enters cells using low-density lipoprotein receptor (LDLR)

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21
Q

What are risk factors for a secondary invader infection of URT

A

1- post viral infection (damaged URT from a cold therefore normal flora can worsen situation)
2- compromised immune response (AIDS, cancer chemotherapy, young/elderly, alcoholics)
3- foreign body insertion e..g endotracheal tube for mechanical ventilation.

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22
Q

Name 6 common URTI

A 
Common cold 
Oral candidiasis 
Sinusitis
Pharyngitis/tonsillitis
Acute epiglottitis
Otitis (media, externa)
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23
Q

What microorganisms can cause otitis externa

A

S.aureus or P. Aureginosa

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24
Q

What is the antibiotic therapy of choice for otitis externa for s aureus (considering both penicillin allergy/no penicillin allergy)

A

penicillin allergy - azithromycin

no penicillin allergy - flucloxacillin (most common)

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25
Q

What is the antibiotic therapy for suspected p aureginosa causing otitis externa

A

Ciprofloxacin

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26
Q

What is the difference between otitis externa/media

A

Media is inflammation of the middle ear (often caused by h influenzae, s pneumoniae, s pyogenes, moraxella catarrhalis) accompanied by an ear infection

Externa is inflammatory process of external auditory canal. Discomfort with erythema and swelling of the canal with variable discharge

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27
Q

What is the incubation period common cold

A

2-4 days

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28
Q

Common symptoms of common cold

A

Nasal discharge, sneezing and sore throat, maybe temp and headache

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29
Q

What two viruses can cause common cold

A

RSV and rhinovirus

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30
Q

What two further infections can be caused by the infection descending in URT

A

Laryngitis and tracheitis

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31
Q

What is the treatment for common cold

A

Supportive. Not antibiotics. Paracetamol.

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32
Q

What is the clinical manifestation of oral candidiasis

A

Raw inflamed mucous membranes, white fungal plaques

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33
Q

What are the predisposing factors for oral candidiasis

A

Broad spectrum antibiotic use (kill normal bacterial flora but allow fungal species to grow)
Contraceptive pill
Systemic steroids
Chemotherapy
Immunosuppression e.g HIV, extremes of age

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34
Q

What does oral candidiasis infection indicate in HIV patients

A

they are changing from HIV patients to AIDS patients

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35
Q

What organism causes oral candidiasis

A

C albicans

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36
Q

What treatment is used for oral candidiasis (also consider for severely immunocompromised patients)

A

Nystatin or clotrimazole pastilles (1 pastille, 4 times a day, for up to 7 days)

HIV patients with severe oral thrush use fluconazole injected intravenously for systemic effect ata dosage of 100mg.

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37
Q

What are the clinical manifestations of sinusitis

A

Facial pain, localised tenderness and swelling

Big swollen red eye on lecture

38
Q

What organisms cause sinusitis

A

Usually viral! Influenza viruses.

But bacterial can occur due to secondary invaders H. Influenzae and S pneumoniae.

39
Q

Name a complication with bacterial sinusitis that can occur

A

Can migrate into brain and get meningitis

40
Q

How can viral sinusitis be distinguished from bacterial

A

Take a clinical sample (sinus washout) and culture on a plate, if dont grow any bacteria likely to be viral.

41
Q

What is the treatment required for viral and bacterial

A

sinusitis viral = supportive
Bacterial invaders =
1- amoxicillin 125-250mg tds (beta lactam) for 3-7 days.
2- augmentin (amoxicillin + clavulanic acid) for beta lactamase producing bacteria 250mg for 3-7days.
3- doxycycline (if allergic to others) 100mg daily, 3-7days
4- erythromycin 250-500mg 3-7 days (if allergic to others)

42
Q

What are the clinical manifestations of pharyngitis/tonsilitis

A

Common in children, fever, sore throat, cervical lymphadenopathy and purulent discharge

43
Q

What is cervical lymphadenopathy and what condition is it associated with

A

Swollen lymph nodes in the neck associates with pharyngitis/tonsillitis

44
Q

What microorganisms cause pharyngitis/tonsillitis

A

Viruses - main cause e.g. Adenovirus

Bacteria - group A streptococcus pyogenes (common) and Neisseria gonorrhoeae (rare)

45
Q

What is the treatment for viral and bacterial pharyngitis/tonsillitis

A

Viral : no treatment.
Bacteria: penicillin V: 500mg qds/10days
Cephalexin 500mg qds/10days
Erythromycin 500mg qds/10days

46
Q

What are post streptococcal tonsilitis complications and why do they occur

A 
Occur because of poor/inadequate treatment. 
1- peritonsillar abscess (PTA, quinsy) 
2- rheumatic fever (autoimmune) 
Glomerulonephritis (autoimmune) 
4- scarlet fever (toxin associated)
47
Q

What is quinsy a nickname for and what is it

A

peritonsillar abscess in post streptococcal complications. Quinsy is where tonsils ae very inflamed and full with bacteria.

48
Q

With quinsy what do you need to do before treating with antibiotics

A

Antibiotics cant get into inflamed tonsils so need to surgically remove

49
Q

What is strawberry tongue and what disease is it associated with

A

Red inflamed tongue after white has been scraped off associated with post streptococcal complications

50
Q

Name some of the clinical symptoms of glomerulonephritis caused as a post streptococcal complications

A

Target organ is kidney -
Inflammation of glomeruli, edema, hypertension, haematuria and proteinuria

Immune complexes of strep antigens deposit in glomeruli activating complement cascade

51
Q

If strep throats are not treated properly what disease can occur

A

Scarlet fever

52
Q

Group a strep properties

A

Gram positive
Thick peptidoglycan with covalently bound teichoic acid. M protein is anchored in cytoplasmic membrane and is a helical coiled coil fibrillar protein

53
Q

Which two letters fit in the gaps to describe the adhesion proteins of group A strep:
_-protein and _-protein

A

F and M

54
Q

What does F protein of group a strep recognise

A

FIBRONECTIN IN PHARYNX

55
Q

Which is group a strep primary adhesion molecule

A

F protein

56
Q

What does M protein protrude as

A

Fimbrae/pili

57
Q

How many classes of m protein are there

A

Two. M class I and M class II.

58
Q

What does M protein mediate

A

Adherence to epithelial cells/ECM

59
Q

How many immunological types are there and at what end of the M protein

A

> 80 at the amino end

60
Q

What disease can M protein class I cause that M protein class II cannot

A

Rheumatic fever.

61
Q

What molecules does group A strep use to to attach?

A 
Lipoteichoic acid (important pro-inflammatory molecule) help bind to fibronectin alongside F protein.
Glyceraldehyde 3-phosphate dehydrogenase (G3-PD) and enolase which binds plasminogen.
62
Q

What mechanisms does group a strep use to evade host defence

A

1- hyaluronic acid capsule: identical to human substance avoiding immune detection, bind to cellular hyaluron receptor; CD44 mediating adherence and invasion

2- immunoglobulin binding proteins: binds to the FC region of IgG and IgA preventing opsonisation

3- C5a peptidase surface protein that inactivates c5a (a potent chemotactic peptide) thus limiting the recrui,ent of macrophages and neutrophils to the site of infection

4- M protein binds Factor H of complement cascade which degrades C3b. Also as it binds fibrinogen, M protein blocks deposition of C3b

63
Q

What virulence factors are SECRETED by group a strep

A

1- streptolysin O: MW 60,000, haemolytic toxin, cardiotoxic and antigenic
2- DNAase : hydrolyse nucleic acids, possible spred factor. Use DNA by products for nutrition.
3- Streptokinase : antigenic protein combines 1:1 with plasminogen to make functional plasminogen, can hydrolyse fibrin and other host proteins protease
4- hyaluronidase: dissolves cellular hyaluronic acid and promotes movement of bacteria through tissue
5-STREPTOCOCCAL PYROGENIC EXOTOXINS (SPEs)

64
Q

Streptococcal pyrogenic exotoxins are found on which microorganism

A

Strep pyogenes

65
Q

Name some of the streptococcal pyrogenic exotoxins

A

SPEa, SPEb, SPEc, SPEf, SPEg, SPEm etc

66
Q

Streptococcal pyrogenic exotoxins are superantigens, true or false

A

True

67
Q

Approximately how many T cells are activated upon superantigens interaction

A

1:5 or 20% of T cells.

68
Q

Why do superantigens produce a high t cell activated response

A 
Evade digestion process therefore get none specific binding therefore get more t cells activated and more inflammation. 
Directly bind tcr with mhc class II.
69
Q

SPEs are not responsible for scarlet fever, true or false

A

False. They are responsible

70
Q

Which microorganism is most likely to caste tonsilitis

A

Group A strep pyogenes

71
Q

What sample is taken for expected GAS causing tonsilitis

A

Throat swab in stuarts medium

72
Q

What category pathogen is Ss pyogenes

A

Category 2

73
Q

What is the appropriate growth medium for GroupA strep pyogenes

A

Blood agar enriched.
Neomycin selective agar with added bacitracin disc (GAS is sensitive to bacitracin but normal flora isnt) so get zone if GAS is present

74
Q

How does s pyogenes appear on agar from a THROAT SWAB inoculation

A

Colony appear 1-2mm, grey colonies with an entire edge with a large zone of beta haemolysis

75
Q

How does s pyogenes appear on agar with bacitracin disc.

A

Large zone of inhibition - presumed GAS

76
Q

What is the ‘full identification’ step for S pyogenes

A

lancefield grouping: detect group specific CHO cell wall antigen

77
Q

What is the group A CHO antigen composed of

A

Repeating units of N-acetylglucosamine-rhamnose

78
Q

What acid is used in lancefield grouping to strip away surface carbohydrate to test for antibody agglutination

A

Nitrous acid is used

79
Q

What does a positive result for GAS look like in lancefield grouping

A

Agglutination within the A circle.

80
Q

Name 3 common types of antibiotics for treating URTI

A

Beta lactams
Tetracyclines e.g. Doxycycline
Macrolides - Arthromyocin

81
Q

What do beta lactams bind to cause cell lysis

A

PBP

82
Q

What are the side effects of using broad spectrum beta lactams

A

Diarrhoea and vomiting as normal flora is sensitive.

83
Q

State the link between the contraceptive pill, beta lactams, macrolides, and tetracyclines

A

The antibiotics can reduce the effectiveness of the oral contraceptive, suggest use other form of contraception whilst on beta lactams, macrolides or tetracyclines

84
Q

Name some beta lactam antibiotics

A

Penicillin
Amoxicillin
Cephalosporins
Augmentin

85
Q

Name some tetracycline antibiotics

A

Tetracycline
Doxycycline
Oxytetracycline

86
Q

Tetracycline is a bacteriostatic antibiotic . True or false

A

True

87
Q

What does tetracycline inhibit

A

Protein synthesis - prevent aminoacyl tRNA from binding to the 30S subunit of the ribosome

88
Q

Why are tetracyclines not recommended for children under 12 yrs and pregnant women

A

Cause deposits in growing teeth and bone so become stained

89
Q

What is the MOA of macrolides

A

Bacteriostatic/bacteriocidal as inhibit protein synthesis by binding to rRNA in the 50s subunit and blocks translocation preventing the release of tRNA

90
Q

Which set of antibiotics is often used as an alternative to penicillin

A

Macrolides

91
Q

Name some macrolides antibiotics

A

Azithromycin (used to treat chlamydia)
Erythromycin
Clarythromycin

Clinical Micro (9 decks)

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