Lecture 9: Respiratory Pathogens Flashcards
Bordetella pertussis and Mycobacterium tuberculosis.
Give 3 examples of Upper Respiratory Tract Infections.
Otitis Media, Tonsilitis, Laryngitis.
Give 3 examples of Lower Respiratory Tract Infections.
Bronchitis, Bronchiolitis and Pneumonia.
What is Otitis Media and why is this considered a respiratory tract infection?
Middle-ear infection. Anything on the inside of your ear drum is considered a respiratory tract infection.
What type of bacteria are Bordetella pertussis, what environment do they live in?
Very small, Gram-Negative coccus bacteria, obligate aerobe. It is also catalase positive.
Where does Bordetella pertussis colonise?
Ciliated epithelium of the human respiratory tract.
How does does Filamentous Haemagglutinin (FHA) help Bordetella pertussis to colonise the respiratory tract?
Binds to galactose on the glycolipid sulphatide of ciliated cells, aiding in colonisation.
What happens in the toxemic stage of Bordetella pertussis infection?
The bacteria are gone, but toxins remain, causing inflammation, necrosis, and immune disruption.
Why are antibiotics ineffective in the toxemic stage of Bordetella pertussis infection?
The bacteria have already been cleared, but toxins continue to cause symptoms.
How can Bordetella pertussis infection be prevented?
Vaccination with Tdap (Tetanus-diphtheria-acellular pertussis).
Why did Bordetella pertussis cases increase post-pandemic?
Reduced transmission during the pandemic led to lower natural immunity, increasing susceptibility.
Thick about ways in which bacteria are classified.
What are the characteristics of Mycobacterium tuberculosis?
- Gram-Positive.
- Obligate aerobes
- Do not form spores.
- Non-motile (no flagella)
- No capsule.
- Bacilli
- Thick waxy cell wall formed from mycolic acids that resists gram stain (unusual for gram-positive bacteria).
How does Mycobacterium tuberculosis evade the immune system?
- Bacteria is engulfed by alveolar macrophages, but blocks phagosome-lysosome fusion, enabling survival.
- Bacteria induce macrophage fusion and release of cytokines, which recruits T cells.
- Formation of granuloma.
- Long-term damage to lungs as granulomas cause chronic inflammation (lung tissue basically replaced by scar tissue).
What is BCG and how effective is it?
Vaccine that is effective against TB meningitis but poor against pulmonary TB.
What is Multi-Locus Sequence Typing (MLST)?
A method of sequencing housekeeping genes to differentiate bacterial strains with low mutation rates.
What is meant by the term ‘pleomorhpic’?
The ability of an organism, such as a bacterium, to exist in multiple shapes or forms rather than having a single, fixed shape.
Invasive Adenylate Cyclase is a toxin produced by Bordetella pertussis, how does is damage host cells?
It binds to calmodulin, and increases cAMP, leading to immune suppression and reduced phagocytosis.
What is the function of Lethal Toxin produced by Bordetella pertussis?
A large multi-unit protein that causes localised tissue necrosis and generalised inflammation.
What is the role of Tracheal Cytotoxin?
A peptidoglycan fragment that stops the ciliary beat of respiratory epithelial cells, leading to mucus buildup and persistent coughing.
What is the mode of action of Pertussis Toxin?
AB5 exotoxin. It binds to host cell and is endocytosed. The A-subunit binds to Gα (i) protein causing ADP ribosylation. This causes prolonged inactivated of Gα (i) protein, leading to an increase in cAMP. Results in increased mucus production in respiratory tract.
What do the terms Catarrhal and Paroxysmal refer to?
Catarrhal: Inflammation of the mucous membranes -> excessive mucus production. Paroxysmal: Refers to sudden, intense episodes or attacks of symptoms.
Describe how Mycobacterium tuberculosis grows in liquid culture.
Forms serpentine cords due to presence of a protein called cord factor. Very simple nutritional requirements but extremely slow growing.
What are the clinical features of pulmonary tuberculosis?
- In primary TB 90% of infected individuals are asymptomatic.
- Symptoms experienced: Chronic cough, weight loss (reduced respiration due to reduced lung function).
- In the long-term granulomas lead to chronic inflammation: scar tissue replaces normal lung tissue - this canbe seen on chest x-ray.
Describe the structure of granulomas (tubercules) formed by action of Mycobacterium tuberculosis.
Center: Infected macrophages.
Middle: T cells
Outer layer: Fibrin & calcium deposition (walling off infection)
