The lungs are prone to infections because lung tissue is designed to interact with the outside world (via breathing) but is fragile enough that it can be damaged easily. Lung infections, also known as infectious pneumonia, can range from fairly mild to life-threatening. There are many different organisms that can infect the lungs.
Bacteria
The Mayo Clinic explains that many lung infections are caused by bacteria. The most common type of bacteria that causes lung infections is called Streptococcus pneumoniae. This can cause a fairly serious lung infection, although there is a vaccine to help ward off this type of bacteria. Other bacteria can cause less severe infections, commonly termed walking pneumonia because the infection rarely causes the patient to require bed rest. The American Lung Association notes that bacteria that can cause this type of lung infection include Mycoplasma pneumoniae, Legionella pneumophila and Chlamydophila pneumoniae. Other bacteria that can infect the lungs include Streptococcus pyogenes, Staphylococcus aureus, Neisseria meningitidis, Moraxella catarrhalis, Haemophilus influenzae and Klebsiella pneumoniae.
Viral Infections
Viruses also can infect the lungs, leading to viral pneumonia. PneumoniaSymptoms.org notes that viral lung infections tend to be less severe than bacterial infections, although some can be life-threatening. This is especially true for patients who are pregnant or have heart or lung problems. One common cause of a viral lung infection is strains of the influenza viruses (both type A and type B). Other common viral lung infections are caused by the respiratory syncytial virus, parainfluenza virus, Hantavirus, adenovirus and cytomegalovirus. Some viruses, such as Epstein-Barr, herpes simplex and varicella-zoster, can infect the lungs while also affecting other tissues throughout the body.
Fungi
A number of fungi can also infect the lungs. Fungal infections of the lungs tend to be divided into opportunistic (infections that affect only people with weakened immune systems) and endemic (which can infect people with weak or healthy immune systems). Opportunistic fungal infections include those caused by Cryptococcus neoformans, Candida, Aspergillus and Mucor fungi. Endemic fungal infections can be caused by Coccidioides immitis, Paracoccidioides brasiliensis, Histoplasma capsulatum and Blastomyces dermatitidis.
Mycobacteria
Mycobacteria are a special subset of bacteria that can cause serious lung infections. For example, Mycobacterium tuberculosis causes tuberculosis. This infection can cause serious lung damage and also can spread throughout the body if it is not properly treated.
