Like in meningitis, how do these bugs travel so well into the lungs?
Certain types of meningitis are unique in that the microbes become suspended in the air and can remain that way for an extended period of time. Disease that spread in an airborne fashion, such as meningitis and tuberculosis, are delivered to your lungs by simply breathing.
For other diseases, such as bacterial pneumonia, the migration to the lungs is more difficult. The trachea is lined with cells that secrete mucous and other cells that have microscopic hair-like projections. Mucous is constantly produced and swept outward. This catches most microbes and expels them from the respiratory tract before they can cause problems.
Diseases make it past this system when we don’t expel the mucous in a timely manner. This can be because we are lying in bed for prolonged periods of time, after a surgery for example, or when it hurts to cough as with fractured ribs or other chest injuries.
There are several other things that can make it easier for bacteria to enter the lungs, but this is what it has to overcome.