Lecture 3 URTI Flashcards
What is the most common cause of step throat
Group A Strep
The LRT has a normal flora, true or false?
False. LRT does not have a normal flora ‘sterile site’ but the URT does.
What part of the respiratory tract helps keeps us uninfected.
Mucus and mucociliary tract
What is the role of the epiglottis
Stop food going into the lungs
What is inflammation of the pharynx called?
Pharyngitis (sore throat)
What microorganisms commonly cause acute epiglottitis
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.
Name 3 microorganisms that are ‘common residents’ of the URT
Viridians streptococci
C albicans (mouth)
Haemophilus influenzae
Another example is anaerobic microorganisms (e.g.. bacteroides deep within the gum)
Name 2 microorganisms that are ‘occasional residents’ of the URT
Streptococcus pyogenes
Streptococcus pneumoniae
(TRUE PATHOGENS - CARRY FOR SOME TIME THEN PASS ON TO SOMEONE ELSE)
Which microorganisms are associated with colonisation and ‘superinfection’ following antibiotic treatment?
1- coliforms (e. Coli)
2- pseudomonas spp.
3- candida albicans (oral thrush)
Name 3 microorganisms of URT that can be used as part of friend vs foe argument
Candida albicans
Haemophilus influenzae
Streptococcus mutans (normally colonise mouth)
What dental disease can S. mutans cause and why
Dental caries when teeth aren’t brushed properly so s mutans can adhere to enamel and cause biofilms.
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
1- >50% of people
2- <10%
3- less than 1%
State the difference between primary and secondary invaders of URT
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
Briefly describe how primary invaders are capable of causing disease
(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)
Approximately how many different antigenic types are there of rhinovirus
100
What 4 proteins make up the viral capsid that encases the RNA genome
VP1, VP2, VP3, VP4
What is the role of VP1, VP2 AND VP3 proteins in rhinovirus function
They account for virus antigenic diversity
What is the role of VP4 in rhinovirus function
Anchors the RNA core to the capsid.
A canyon in which of the proteins of rhinovirus serves as the site of attachment for cell surface receptors
VP1.
What percentage of HRV serotypes utilise the cell surface receptor ICAM1, and what is the other cell surface receptor used by the ‘minor group’
90% use ICAM-1
Minor group attaches to an enters cells using low-density lipoprotein receptor (LDLR)
What are risk factors for a secondary invader infection of URT
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.
Name 6 common URTI
Common cold Oral candidiasis Sinusitis Pharyngitis/tonsillitis Acute epiglottitis Otitis (media, externa)
What microorganisms can cause otitis externa
S.aureus or P. Aureginosa
What is the antibiotic therapy of choice for otitis externa for s aureus (considering both penicillin allergy/no penicillin allergy)
penicillin allergy - azithromycin
no penicillin allergy - flucloxacillin (most common)
What is the antibiotic therapy for suspected p aureginosa causing otitis externa
Ciprofloxacin
What is the difference between otitis externa/media
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
What is the incubation period common cold
2-4 days
Common symptoms of common cold
Nasal discharge, sneezing and sore throat, maybe temp and headache
What two viruses can cause common cold
RSV and rhinovirus
What two further infections can be caused by the infection descending in URT
Laryngitis and tracheitis
What is the treatment for common cold
Supportive. Not antibiotics. Paracetamol.
What is the clinical manifestation of oral candidiasis
Raw inflamed mucous membranes, white fungal plaques
What are the predisposing factors for oral candidiasis
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
What does oral candidiasis infection indicate in HIV patients
they are changing from HIV patients to AIDS patients
What organism causes oral candidiasis
C albicans
What treatment is used for oral candidiasis (also consider for severely immunocompromised patients)
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.
What are the clinical manifestations of sinusitis
Facial pain, localised tenderness and swelling
Big swollen red eye on lecture
What organisms cause sinusitis
Usually viral! Influenza viruses.
But bacterial can occur due to secondary invaders H. Influenzae and S pneumoniae.
Name a complication with bacterial sinusitis that can occur
Can migrate into brain and get meningitis
How can viral sinusitis be distinguished from bacterial
Take a clinical sample (sinus washout) and culture on a plate, if dont grow any bacteria likely to be viral.
What is the treatment required for viral and bacterial
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)
What are the clinical manifestations of pharyngitis/tonsilitis
Common in children, fever, sore throat, cervical lymphadenopathy and purulent discharge
What is cervical lymphadenopathy and what condition is it associated with
Swollen lymph nodes in the neck associates with pharyngitis/tonsillitis
What microorganisms cause pharyngitis/tonsillitis
Viruses - main cause e.g. Adenovirus
Bacteria - group A streptococcus pyogenes (common) and Neisseria gonorrhoeae (rare)
What is the treatment for viral and bacterial pharyngitis/tonsillitis
Viral : no treatment.
Bacteria: penicillin V: 500mg qds/10days
Cephalexin 500mg qds/10days
Erythromycin 500mg qds/10days
What are post streptococcal tonsilitis complications and why do they occur
Occur because of poor/inadequate treatment. 1- peritonsillar abscess (PTA, quinsy) 2- rheumatic fever (autoimmune) Glomerulonephritis (autoimmune) 4- scarlet fever (toxin associated)
What is quinsy a nickname for and what is it
peritonsillar abscess in post streptococcal complications. Quinsy is where tonsils ae very inflamed and full with bacteria.
With quinsy what do you need to do before treating with antibiotics
Antibiotics cant get into inflamed tonsils so need to surgically remove
What is strawberry tongue and what disease is it associated with
Red inflamed tongue after white has been scraped off associated with post streptococcal complications
Name some of the clinical symptoms of glomerulonephritis caused as a post streptococcal complications
Target organ is kidney -
Inflammation of glomeruli, edema, hypertension, haematuria and proteinuria
Immune complexes of strep antigens deposit in glomeruli activating complement cascade
If strep throats are not treated properly what disease can occur
Scarlet fever
Group a strep properties
Gram positive
Thick peptidoglycan with covalently bound teichoic acid. M protein is anchored in cytoplasmic membrane and is a helical coiled coil fibrillar protein
Which two letters fit in the gaps to describe the adhesion proteins of group A strep:
_-protein and _-protein
F and M
What does F protein of group a strep recognise
FIBRONECTIN IN PHARYNX
Which is group a strep primary adhesion molecule
F protein
What does M protein protrude as
Fimbrae/pili
How many classes of m protein are there
Two. M class I and M class II.
What does M protein mediate
Adherence to epithelial cells/ECM
How many immunological types are there and at what end of the M protein
> 80 at the amino end
What disease can M protein class I cause that M protein class II cannot
Rheumatic fever.
What molecules does group A strep use to to attach?
Lipoteichoic acid (important pro-inflammatory molecule) help bind to fibronectin alongside F protein. Glyceraldehyde 3-phosphate dehydrogenase (G3-PD) and enolase which binds plasminogen.
What mechanisms does group a strep use to evade host defence
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
What virulence factors are SECRETED by group a strep
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)
Streptococcal pyrogenic exotoxins are found on which microorganism
Strep pyogenes
Name some of the streptococcal pyrogenic exotoxins
SPEa, SPEb, SPEc, SPEf, SPEg, SPEm etc
Streptococcal pyrogenic exotoxins are superantigens, true or false
True
Approximately how many T cells are activated upon superantigens interaction
1:5 or 20% of T cells.
Why do superantigens produce a high t cell activated response
Evade digestion process therefore get none specific binding therefore get more t cells activated and more inflammation. Directly bind tcr with mhc class II.
SPEs are not responsible for scarlet fever, true or false
False. They are responsible
Which microorganism is most likely to caste tonsilitis
Group A strep pyogenes
What sample is taken for expected GAS causing tonsilitis
Throat swab in stuarts medium
What category pathogen is Ss pyogenes
Category 2
What is the appropriate growth medium for GroupA strep pyogenes
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
How does s pyogenes appear on agar from a THROAT SWAB inoculation
Colony appear 1-2mm, grey colonies with an entire edge with a large zone of beta haemolysis
How does s pyogenes appear on agar with bacitracin disc.
Large zone of inhibition - presumed GAS
What is the ‘full identification’ step for S pyogenes
lancefield grouping: detect group specific CHO cell wall antigen
What is the group A CHO antigen composed of
Repeating units of N-acetylglucosamine-rhamnose
What acid is used in lancefield grouping to strip away surface carbohydrate to test for antibody agglutination
Nitrous acid is used
What does a positive result for GAS look like in lancefield grouping
Agglutination within the A circle.
Name 3 common types of antibiotics for treating URTI
Beta lactams
Tetracyclines e.g. Doxycycline
Macrolides - Arthromyocin
What do beta lactams bind to cause cell lysis
PBP
What are the side effects of using broad spectrum beta lactams
Diarrhoea and vomiting as normal flora is sensitive.
State the link between the contraceptive pill, beta lactams, macrolides, and tetracyclines
The antibiotics can reduce the effectiveness of the oral contraceptive, suggest use other form of contraception whilst on beta lactams, macrolides or tetracyclines
Name some beta lactam antibiotics
Penicillin
Amoxicillin
Cephalosporins
Augmentin
Name some tetracycline antibiotics
Tetracycline
Doxycycline
Oxytetracycline
Tetracycline is a bacteriostatic antibiotic . True or false
True
What does tetracycline inhibit
Protein synthesis - prevent aminoacyl tRNA from binding to the 30S subunit of the ribosome
Why are tetracyclines not recommended for children under 12 yrs and pregnant women
Cause deposits in growing teeth and bone so become stained
What is the MOA of macrolides
Bacteriostatic/bacteriocidal as inhibit protein synthesis by binding to rRNA in the 50s subunit and blocks translocation preventing the release of tRNA
Which set of antibiotics is often used as an alternative to penicillin
Macrolides
Name some macrolides antibiotics
Azithromycin (used to treat chlamydia)
Erythromycin
Clarythromycin
