Final answer:
The most commonly found bacterial cause of pneumonia is Streptococcus pneumoniae, which is a typical part of the human respiratory tract's normal flora and leads to a condition known as pneumococcal pneumonia.
Step-by-step explanation:
Bacterial Causes of Pneumonia
The most commonly found bacterial cause of pneumonia is Streptococcus pneumoniae. This gram-positive bacterium is often part of the normal flora of the human respiratory tract. The bacteria are characterized by their lancet shape and usually appear in pairs. Pneumococcal pneumonia, caused by Streptococcus pneumoniae, typically begins by colonizing the bronchioles and subsequently spreading to the alveoli. The infection then progresses as the bacteria's polysaccharide capsule impedes phagocytic clearance, and various virulence factors contribute to the disease's development, such as pneumolysin O, which damages host cells and promotes inflammation. This inflammation leads to accumulation of neutrophils and red blood cells in the alveoli, resulting in respiratory symptoms, a productive cough, and sometimes bloody sputum.
While other bacteria such as Pseudomonas aeruginosa, Mycoplasma pneumoniae, and Klebsiella pneumoniae can also cause pneumonia, they are less common or associated with specific conditions. For example, Pseudomonas aeruginosa is often associated with cystic fibrosis or hospital-acquired infections, especially in patients using ventilators, and mycoplasma pneumonia is known for causing milder forms of pneumonia, often referred to as 'walking pneumonia'.