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Bacterial Diseases of the Lower Respiratory Tract

Diseases Of The Lower Respiratory Tract
Lower respiratory tract consists of larynx, trachea, bronchial tubes and alveoli (air sacs that make up the lung tissue).

Bacterial Diseases
Pertussis (whooping cough, per-thoroughly and tussis-cough)

Causative organism is Bordetella pertussis which is a small obligately aerobic capsulated gram negative coccobacillus.
It is primarily a childhood disease and can be quite severe. Initial stage resembles a common cold.
Mortality rates among children is quite high.

Disease is transmitted by inhaling pathogens expelled by the coughing of the infected person.
Transmission rate is 90% among non-immune contacts.

Tuberculosis
Causative organism, Mycobacterium tuberculosis is a slender acid­ fast rod and obligate aerobe which is a slow grower.
On the surface of the liquid media, their growth appears mold-like hence the name Mycobacterium.
TB is most commonly acquired by inhaling the tubercle bacillus.

Bacterial pneumonias Pneumonia is a pulmonary infection caused by bacteria.
Pneumococcal pneumonia
Caused by S. pneumoniae which is a gram positive capsulated ovoid bacterium in pairs.
Involves bronchi and alveoli with high fever, breathing difficulty and chest pain.
Sputum is rust colour because of blood coughed up from lungs.

H. Influenzae pneumonia
Caused by gram negative coccobacilli.
Has similar symptoms as common cold.

Mycoplasmal pneumonia
Causative organism is Mycoplasma pneumoniae.
They are fastidious organisms which lack cell wall and show very small colonies on solid media.
The disease is endemic and is the common cause of pneumonia in children.
Transmitted by airborne droplets.
Infects the upper respiratory tract initially with low fever, cough and headache followed by the lower respiratory tract infection.

Legionellosis
Legionnaires disease is caused by an aerobic gram negative rod Legionella pneumophila. (pneumo-Iung, phila-Ioving).

Characterised by high fever of 105°F, cough and general symptoms of pneumonia.
Microbes can grow in the water of air conditioners and cooling towers, the cause of epidemic in hotels and hospitals through airborne transmission.

Psittacosis (ornithosis)
Term is derived from the diseases associated with psittacine birds (parakeets, parrots).
Causative agent is Chlamydia psittaci which is a gram negative obligate intracellular bacterium.
They produce tiny elementary bodies as part of their life cycle. These elementary bodies are resistant to environmental conditions, and therefore are transmitted through air.

Psittacosis is a form of pneumonia that causes fevers, headache and chills with delirium (disorientation).

Psittacosis is a form of pneumonia that causes fevers, headache and chills with delirium (disorientation).

One of the most common modes of transmission is inhalation of dried particles from droppings of birds.

Chlamydial pneumonia
Causative organism is Chlamydia pneumoniae.

Shows similar symptoms as pneumonia.

Q fever (query fever)

Caused by a rickettsial member Coxiella burnettii.
Symptoms are undulating fever (1-2 weeks) with chills, chest pain severe headache.
This organism is resistant enough to survive airborne transmission.
This pathogen is a parasite among arthropods (ticks) which transmit the organism to cattle and dairy herds following which the microbes are shed in milk, faeces and urine of infected cattle.
Once the disease is established in a herd, it is maintained by aerosol transmission.
The disease can be spread by inhaling aerosols of microbes generated in dairy barns, especially from placental material at calving time.
Inhaling a single pathogen is enough to cause infection.
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