Lower respiratory tract bacteria 3ish Flashcards
describe the physiology and structure of Mycobacteria
- Weakly gram positive, acid-fast rods
- Lipid rich cell wall which is responsible for acid-fast staining
- Humans are the only reservoir
- person to person transmission via respiratory aerosol droplets (coughs, sneezes, speaking, singing)
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Alveolar macrophage engulf Mtb
- Mtb evades killing
- recrutiement of T and NK cells
- Some alveolar macrophage migrate to hilar lymph nodes leads to systemic dissemination of Mtb
Latent TB infection:
- inability of immune system to kill Mtb
- CD4+, CD8+ and NK cells surround necrotic mass of Mtb infectied macrophage and form a Caseous necrosis
define Latent TB
- inability of immune system to kill Mtb
- CD4+, CD8+ and NK cells surround necrotic mass of Mtb infected macrophage causing caseous necrosis
- forming a Granuloma which prevents further spread
Define Primary TB
Usually asymptomatic
- leads to:
1) Clearance
2) active TB in immunocompromised patients
3) latent TB in most individuals - reactivation upon some immuno-comprimising event or immunosenescence.
Describe CMI’s effect on TB
Control of TB infection:
- Adequate control = granuloma
- inadequate control = active TB/reactivation TB –> dissemination
- Most of the pathology/disease is a direct consequence of CMI response
Define the pathology of Active and Reactivation TB
Active TB and reactivation TB
1) Rapidly dividing Mtb
2) increase CMI activation
3) more caseous necrotic lesions, inflammation
4) tissue damage
Describe the symptoms associated with Active TB
- Gradual onset, variable manifestations
- Fatigue, WEIGHT LOSS, weakness, fever, NIGHT SWEATS, chest pain, and dyspnea
- COUGH - absent or mild with SCANT SPUTUM (severe productive cough with yellow/yellow-green/blood-streaked sputum)
Describe the symtpoms associated with Reactivation TB
Patients can often be asymptomatic for 2-3 years and be infectious
- -> granulomas fall apart, Mtb can move to other parts of the lung, can be expectorated/aerosolized and transmitted to other individuals, can spread systemically
- -> symptoms similar to/same as active TV
How do you diagnose latent TB
- Ghon focus = lung lesion (granuloma seen on chest x-ray as it calcifies)
- Ghon complex = lung lesion and calcification seen in an affected hilar lymph
How do you diagnose active or reactivation TB
- Clinical symtpoms
- Rapid lab tests
- Chest x-ray = focal infiltration with cavitation (often in the apical posterior segment of the upper lobes of both lungs)
- Consider TB in immunosuppressed patients with other diagnosis
- Report known or suspected cases of TB to Health department
Describe the immuno-diagnosis labs for the diagnosis of TB
Tuberculin skin test = intradermal injection of purified protein derivatives (PPD’s)
- BCG-vaccinated people will test positive
IFN-gamma release assay
- measure IFN-gamma release by T-cells in whole blood stimulated with Mtb antigen
- ideal for patients that have been BCG-vacinated
describe the microscopy labs for the diagnosis of TB
- Ziehl Neelsen or Kinyoun stains = acid-fast staining due to lipid rich cell wall
- -> confirms mycobacterial disease but not specific for Mtb
- Nucleic Acid Amplification test
- Culture = Mtb slow growing, contamination issues (10-21 days)
Describe the Treatment of TB
Treatment:
- Isoniazid (INH), ethambutol, pyrazinamide, and rifampin (4 drugs) for 2 months followed by 26 months of INH and rifampin or an alternative drug combination
- -> Isonaizid = prodrug, inhibits mycolic acid synthesis, heptatoxicity
Describe the Prevention of TB
Vaccination:
- BCG-vaccine = mycobacterium bovis
- -> not completely protective
- -> vaccinated individuals test positive in TB skin test
describe TB’s relationship with AIDS
- Primary TB infection risk much greater in HIV infected individuals
- progression to active TB much more likely in HIV infected individuals
- Much greater reactivation risk
- disseminated TB
- Multi- and extended drug resistant strains are prevalent in populations with a high incidence of HIV infection
describe Mycobacterium avium-intracellulare
- Atypical mycobactera
- Nontuberculous mycobacteria
- complex of several mycobacteria
- Pulmonary infection resembling TB in immunocompromised patients or with lung disease
Describe Mycobacterium kansasii
- Atypical mycobacteria
- Nontuberculous mycobacteria
- More common in elderly
- Chronic gradulomatous pulmonary disease
- Seen in COPD patients
Describe Laryngitis, Tracheitis, and Epiglotitis
- Symptoms = Hoarseness, burning retrosternal pain
- Larynx/Trachea have non-expandable cartilage rings in the wall (inflammation, swelling of mucous membranes can lead to obstruction in children)
What are the cause of Laryngitis, tracheitis, and epiglotitis
- Most likely viral
- Less common causes:
GAS, Haemophilus influenzae and Staphylococcus aureus
Describe Haemophilus influenzae serotype B (HiB)
- Gram-negative, coccobacilli
- Fastidious - requires NAD and hemin for growth
- Typed strains = capsule
- Nontypeable = no capsule\
Transmission = via respiratory droplets or direct contact with respiratory secretions
Effects of Haemophilus influenzae serotype B (HiB)
- Conjunctivitis
- Meningitis
- epiglotitis
- purpuric fever
- pneumonia
- Otitis media/sinusitis
describe the virulence factors of Haemophilus influenzae serotype B
LPS
IgA protease
TYPED STRAINS –> polysaccharide capusle polyribosylribitol phosphate (PRP)
Describe the diagnosis and treatment of HiB
- Gram staining and culture of blood, nasopharyngeal swab, sputum, spinal fluid
- Treatment = (high mortality rate)
- -> severe cases = broad-spectrum cephalosporin
- -> less severe cases = amoxicillin (if sensitive)
- Vaccination: Conjugate vaccine = PRP capsule linked to protein carrier
Describe Acute bronchitis
Inflammation of the tracheobronchial tree
- Commonly caused by Mycoplasma pneumoniae
- Symptoms = dry cough, treatment of symptoms
- Sequelae = pneumonia
