Bacteria Home > Bacterial Pneumonia

When pneumonia is caused by Streptococcus pneumoniae, Mycoplasma pneumoniae, or other bacteria, it's called bacterial pneumonia. This illness can affect both children and adults, and is more common during the winter. People with this type of pneumonia usually start to feel better three to five days after starting antibiotics. However, some people will need up to a month before resuming their normal activities.

What Is Bacterial Pneumonia?

Pneumonia is an infection in one or both lungs. It can be caused by a number of different germs, including bacteria, viruses, and fungi. When caused by bacteria, the illness is known as bacterial pneumonia.
Bacterial pneumonia can affect both adults and children (see Pneumonia in Children). It is more common in older adults (over the age of 65), infants, those with chronic conditions (such as COPD, diabetes, or heart disease), and those with a weakened immune system. This type of pneumonia can happen at any time of the year, although it is more common in winter months.

Which Bacteria Cause Pneumonia?

A number of different bacteria can cause bacterial pneumonia. Some are more likely to cause an infection within the community (known as community-acquired bacterial pneumonia), while others are more likely to cause infections within the hospital (known as hospital-acquired bacterial pneumonia).
The bacteria more likely to cause community-acquired pneumonia include:
  • Streptococcus pneumoniae, also known as just pneumococcus (the most common cause of pneumonia worldwide)
  • Mycoplasma pneumoniae, the main cause of walking pneumonia (see Mycoplasma Pneumonia)
  • Haemophilus influenzae
  • Chlamydophila pneumoniae (more common in children under four months of age or over the age of five)
  • Legionella pneumophila
  • Bordetella pertussis (the bacteria that cause whooping cough).
While less common, methicillin-resistant Staphylococcus aureus (MRSA) is starting to become a more important and concerning cause of pneumonia in children and adults.
Hospital-acquired pneumonia tends to be more serious than community-acquired pneumonia. This is because the person is already sick. Also, hospitals tend to have more germs that are resistant to antibiotics -- a treatment for pneumonia.
Some bacteria that can cause hospital-acquired pneumonia include:
  • Gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, Enterobacter species, Pseudomonas aeruginosa, and Acinetobacter species
  • Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA)
  • Streptococcus species.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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