L9 - chronic respiratory infections Flashcards
TB microbiology
aerobic, non-spore-forming, non-motile bacillus
TB slow growing
generation time is 15-20 hours compared to most bacteria having 30mins-1hours
How is TNB spread
in aerosol from an infected individual’s lung to another lung via spitting, sneezing, plates, etc
Smear positive
17-50% of household contacts becoming infected
Smear negative
<5%
TB immunology
Mycobacteria are phagocytose by macrophages and trafficked to a phagolysososme, which the host aims to kill through microbicidal molecules and acidification
Digestion and degradation by proteases results in generation of antigens for presentation to T cells
Mtb and phagolysosomes
MTb has adapted to the intracellular environment and aims to withstand the phagolysosomal killing and escapes to the cytosol
Mtb and effective immunity
requires CD4 T cells which generate interferon gamma and this helps activate intracellular killing by macrophages, this can be successful or fail but is mostly partial success
Effective immunity partial success
where the MTb don’t die but are kept inactive within a granuloma
Pulmonary TB infection only
Bacilli settle in lung and are sealed in by macrophages and lymphocytes, containing and killing the majority of infecting bacilli
Pulmonary TB infection in people
majority of people mount an effective immune response that encapsulates and contains the organism forever
>95% do not have any disease
Granulomas
lesions that arise in a response that tries to contain mcobacteria
Langhans giant cells
giant multinucleate cells formed when some macrophages fuse together
Highly stimulated macrophages become…
epithelial cells
T cells and TB
T cells infiltrate the Mtb lesions, fibroblasts laid down around granuloma ‘wall off’
the central tissue may necroses and form a ‘nauseating’ granuloma
Pulmonary TB
2-5 develop clinically evident primary pulmonary disease
Phagocytosis of pulmonary TB
macrophages phagocytose bacilli but fail to kill them
bacilli contained macrophages drain to mediastinal lymph nodes which enlarge as they engage the T cell response
T cells activate which macrophages coalesce to form a granuloma
Granuloma formation most likely to occur in…
the lung apex as there is more air and less blood supply/immune cells
cavity formation
granulomas grow to form a cavity, which is full of TB bacilli which are expelled when a patient coughs
bacilli taken in lymphatics to hilarious lymph nodes
Gram staining acid fast bacilli Mtb
high lipid content with mycelia acids in cell walls make it resistant to staining
slightly curved, beaded bacilli, v forms
Slow growth in culture
means need decontamination steps to kill off other rapid-growing bacteria
Solid culture L. J. Sple
egg-based Lowenstein Jensen, agar-based, from microscopy positive material 2-4 weeks and from microscopy negative material 4-8 weeks
Liquid culture MGIT
1-3 weeks and automated systems
Nucleic acid detection
amplification using PCR, purifies and concentrates MTb, sonicates to release genomic material then performs PCR
rapid MTb result and detects Rifampicin resistance using fluorescence
used for TB endemicc countries
Haematogenous dissemination
occurs if TB is not contained and leads to serious non-pulmonary disease
this may happen after primary infection or after reactivation
TB settling in lung apex
can be taken into hilarious lymph nodes to result in genito-urinary TB
can also enter lung resulting in TB meningitis, military TB and pleural TB
Lifetime TB risk
10% risk then 0.1% per year after first year
TB reactivation risks
age, malnutrition, intensity of exposure, immunosuppression
Nocardiosis infection
bacteria found in the environment, i.e. standing water, decaying plants and soils
slow onset and prolonged
breathe in dust continuing bacteria or when a hospitalised patient is infected from contaminated medical equipment
nocardiosis symptoms
fever, weight loss, night sweats, coughing and chest pain
Nocardiosis spread
can form granulomata in lungs and associated lymph nodes, can spread to other parts of the body e.g. brain abscess
Meliodosis bacteria
Burkholderia pseudomallei
Meliodosis infection
in tropical climates found in contaminated water and soil, spread through direct contact with the contaminated source
Meliodois staining
gram negative rods
Meliodosis symptoms
2-4 weeks development, cough and chest pain, high fever, headache, anorexia and weight loss
pneumonia and lung abscesses
metastatic infection and skin disease
Non-tuberculosis mycobacteria
Mycobacteria that live in the environment in soil or water
Non-tuberculosis mycobacteria symptoms
slow development of chronic cough, coughing up blood, shortness of breath, fatigue, low-grade fever, night sweats and weight loss
Pulmonary hitsplasmosis
dimorphic fungus found worldwide, slower onset pneumonia with visible intrathoracic lymph, pulmonary nodule and cavitary lung disease, granulomata on bopsy
Pulmonary histoplasmosis infection
results in progressive loss of pulmonary function in most patients and death in up to 30% of cases
