Bone covered by mucous membrane Three on each side of nose Warm and humidify air Filters dust, pollen, microbes Turbulence; expose air to respiratory epithelium for longer

Lecture 20 - Respiratory Tract Infections 1 Flashcards by Eleanor Nicklason

What generally causes URT infections?

Viruses

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What causes LRT infection?

Bacteria

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Name some LRT infections

Bronchitis
Bronchiolitis
Pneumonia

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Which viruses commonly cause URT infections?

Parainfluenza
Influenza
Respiratory syncytial virus (RSV)

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Name some URT infections

Rhinitis
Pharyngitis
Laryngitis
Croup
Tracheitis

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Which groups is commonly affected by pneumonia?

• the young
• the elderly
50% of affected people have a defect with their immune defences

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Which agents cause pneumonia?

Mainly Strep. pneumoniae

H. influenzae
Klebsiella pneumoniae
M. tuberculosis
Legionella

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What are the defences in the URT?

Nose: hairs, turbinates

Epiglottis: cough reflex

Respiratory epithelium: cilia, mucous, lysozyme, lactoferrin, sIgA, mucociliary elevator

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What are turbinates?

Bone covered by mucous membrane
Three on each side of nose
Warm and humidify air
Filters dust, pollen, microbes
Turbulence; expose air to respiratory epithelium for longer

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What are the defences in the alveoli?

sIgA
surfactant
complement
alveolar macrophages

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What are the general defences in the LRT?

Alveoli
Blood supply
MALT

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Why is a good blood supply protective in the LRT?

Access to:
• neutrophils
• IgG
• complement

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What is present in the mucous of the URT?

Lysozyme
Lactoferrin
sIgA

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What components of the innate immune system can be compromised, leading to LRT infection?

Defects in defences
• cough reflex
• phagocytes
• cilia

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What is aspiration pneumonia ?

Breathe in the bacteria
No cough reflex when comatose
Such as in heavy drinking

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What is aspiration pneumonia?

When does it happen?

Breathe in contents of URT
• Coma: no cough reflex
• Heavy drinkning

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Where are most bacteria found in the respiratory tract?

Most to least:
• Saliva
• Gingival scrapings
• Tooth surfaces
• Nose washings

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Describe the microbiota of the lower respiratory tract

Sterile

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Which organisms are commonly found in the upper respiratory tract?

G+ cocci

Streptococci

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What are the symptoms of pneumonia?

Fever
Cough
Rapid respiration
Chest pain
Cyanosis
Chest sounds
Shortness of breath

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What happens to the chest x ray in pneumonia

May be abnormal
• Lobar: indicates Strep. pneumoniae infection
• Non-lobar: indicates Infleunza infection

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What do the X rays look like?

Normal: clear

Lobar pneumonia: upper lobe cloudy due to pus. S. pneumoniae

Non-lobar: scatter infiltrate throughout the lungs. Influenza virus

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Describe the onset of pneumonia

Can be either acute or chronic

Depends on the cause

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Where can pneumonia be acquired?

What is the difference?

Community
Hospital

Different organisms and modes of spread

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How do the microbes get in?

* Inhalation * Aspiration of URT contents in coma * Spread along mucous membrane surface * From blood

How is pneumonia diagnosed in a laboratory

1. Specimen collected 2. Microscopy 3. Culture 4. Antigen detection assay using PCR 5. Antibody

How do we diagnose pneumoniae?

Clinical: history, examination, predisposing factors Radiological: chest x ray Lab

What do we look for in the specimen?

Pus cells Bacteria Not looking for epithelial cells --> indicates URT

What sort of sputum is collected

Sputum Blood Serum --> looking for antibodies

Why is S. pneumoniae important?

Most common cause of death in <5s world wide

Where does S. pneumoniae colonise?

Nasopharynx

What is the reservoir of S. pneumoniae?

Humans

Does S. pneumoniae normally cause disease

No | Can be part of normal flora

When are the generalised outcomes of S. pneumoniae infection

Asymptomatic colonisation Disease: • non-invasive • invasive

When does S. pneumoniae cause disease?

When it gains access to normally sterile sites

Do children or adults more commonly carry S. pneumoniae?

Children → 60%

What is invasive disease of S. pneumoniae?

Spread in blood to sites: * Septicaemia * Endocarditis * Septic arthritis * Peritonitis * Meningitis

What is non-invasive disease by S. pneuomniae?

Local disease Spread from nasopharynx to sterile sites * Conjunctivitis * Otitis media (middle ear infection) * Sinusitis * Pneumonia

How many serotyped of S. pneumoniae are there? How is this bacterium typed? What does this mean?

91 By its capsule This means someone can be infected multiple times

What is the morphology of S. pneumoniae?

Gram + coccus Diplococci: in pairs

What does naturally transform able mean?

Readily pick up DNA from the environment | → resistance genes

What are the features of S. pneumoniae?

Catalase negative Facultative anaerobe

How do we differentiate S. pneumoniae from other alpha haemolytic streptococci?

S. pneumoniae is susceptible to Optochin

Which medium do we grow S. pneumoniae on? Describe the colonies

Horse blood agar Alpha haemolysis: Greening colonies

Does S. pneumonia have a capsule?

The virulent ones do have a capsule Unencapsulated S. pneumoniae can't cause disease

Why are the colonies of S. pneumoniae wet and shiny? What is this called?

Due to the capsule Mucoid colonies

What are the different serotypes of S. pneumoniae?

The capsular polysaccharide antigens

What is the role of the capsule

Masks underlying structures | Blocks complement binding

How do we classify S. pneumoniae?

Serotyping

What is the major virulence determinant of S. pneumoniae?

The capsule

What does pyogenic mean?

Pus forming | An extracellular bacterium that evades phagocyte action

What does pyogenic mean?

Pus forming | Induces phagocytes but avoids their action

Give an overview of the Pathogenesis of S. pneumoniae

``` Colonisation Penetration Replication Evasion of immune system Damage Recovery / immunity ```

How does the bacterium colonise?

Cell wall adhesins | Attach to nasopharyngeal and lung mucosa (pneumocytes)

Are capsular antigens cross reactive?

How does the bacterium colonise?

Cell wall adhesins (loads of them) | Attach to nasopharyngeal and lung mucosa (pneumocytes)

What are NETS?

Neutrophil extracellular traps Mainly made of DNA Meshes extruded from neutrophils that trap microbes

How does S. pneumoniae evade NETS?

Releases pneumococcal DNAases that break down NETS

How does S. pneumoniae cause damage?

1. Hydrogen peroxide → local tissue damage 2. Pneumolysin 3. Autolysins: self lyse the bacteria → more inflammation 4. Inflammation

What are the stages of the inflammatory response?

1. Activation of endothelium → exudate 2. Entrance of neutrophils. Ineffective, bacteria persist 3. Neutrophils → impaired lung function, fever 4. Resolution: macrophage action

How do we recover?

* Complement activation → phagocytosis | * Antibodies

What are the complications of S. pneumoniae infection?

1. Pleural effusion: fluid in the pleural space 2. Dissemination: • Into blood and lymphatics • Heart • Meningitis

How is complement effective against the bacterium?

CRP (c reactive protein) eventually triggers the cascade by binding to the cell wall

How do we detect s. pneumoniae in the lab?

Growth on HBA • greening, alpha haemolysis • sensitivity to optochin Serotyping Gram stain Capsule stain

How is S. pneumoniae infection treated?

Supportive treatment: • Bronchodilators • Oxygen • Analgesics Antimicrobials: • Cephalosporins • Penicillins → however resistance Vaccination

Does S. pneumoniae cause pharyngtis?

Not normally | It is part of the normal flora and is kept in check

What is the connection of S. pneumoniae with Australian Indigneous populations?

Very high incidence of invasive disease

Describe how pneumolysin causes damage to the host

Released later in growth Cytotoxic to endothelial cells (with cholesterol) Triggers complement

Describe how autolysins cause damage to the host

Induce bacterial cell death Release cell wall components → Trigger complement cascade

Describe how inflammation leads to host tissue damage

Inflammation sparked by pneumolysin and CRP binding to dying cells Big inflammatory response

Describe how inflammation leads to host tissue damage

Inflammation sparked by pneumolysin and CRP binding to dying cells Big inflammatory response

How does pneumolysin cause damage? When is it released?

* Puts pores in cells with cholesterol in the membrane (endothelium and alveolar cells) * Triggers complement cascade Produced later on

Which proinflamamatory compounds does S. pneumoniae produce?

* Pneumolysin | * Autolysin

What is pneumonia?

Acute inflammation of the lungs, typically, the alveoli

What things decrease the function of the defences in the respiratory tract?

* pre-existing disease (influenza) * smoking * drinking * anaesthesia * immobilisation * immunosuppression * extremes of age

How can heavy drinking put a person a risk of LRT infection?

Aspiration pneumonia | • unconscious, cough reflex isn't working

Is Strep. pneumoniae intra- or extracellular?

Extracellular

Lecture 20 - Respiratory Tract Infections 1 Flashcards

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