Den mest almindelige årsag til bakteriel lungebetændelse er Streptococcus pneumoniae. I denne form for lungebetændelse, er der normalt en pludselig indsættende sygdom med kulderystelser, feber, og produktion af en rust-farvet opspyt. Infektionen breder sig ind i blodet i 20%-30% tilfælde (kendt som sepsis), og i sådanne tilfælde, 20%-30% af disse patienter dør.
To vacciner er tilgængelige til at forhindre pneumokoksygdom: den konjugerede pneumokokvaccine (PCV13) og pneumokokpolysaccharidvaccine (PPV23; Pneumovax). Den konjugerede pneumokokvaccine er en del af almindeligt børnevaccinationsprogram tidsplan i USA. og anbefales til alle børn < 2 years of age and children 2-4 years of age who have certain medical conditions. The pneumococcal polysaccharide vaccine is recommended for adults at increased risk for developing pneumococcal pneumonia including the elderly, people who have diabetes, chronic heart, lung, or kidney disease, those with alcoholism, cigarette smokers, and in those people who have had their spleen removed. This vaccination should be repeated every five to seven years, whereas the flu vaccine is given annually. Antibiotics often used in the treatment of this type of pneumonia include penicillin, amoxicillin and clavulanic acid (Augmentin, Augmentin XR), and macrolide antibiotics including erythromycin (E-Mycin, Eryc, Ery-Tab, PCE, Pediazole, Ilosone), azithromycin (Zithromax, Z-Max), and clarithromycin (Biaxin). Penicillin was formerly the antibiotic of choice in treating this infection. With the advent and widespread use of broader-spectrum antibiotics, significant medicines resistance has developed. Penicillin may still be effective in treatment of pneumococcal pneumonia, but it should only be used after cultures of the bacteria confirm their sensitivity to this antibiotic. Klebsiella pneumoniae and Hemophilus influenzae are bacteria that often cause pneumonia in people suffering from chronic obstructive pulmonary disease (COPD) or alcoholism. Useful antibiotics in this case are the second- and third-generation cephalosporins, amoxicillin and clavulanic acid, fluoroquinolones (levofloxacin [Levaquin], moxifloxacin-oral [Avelox], and sulfamethoxazole/trimethoprim [Bactrim, Septra]). Mycoplasma pneumoniae is a type of bacteria that often causes a slowly developing infection. Symptoms include fever, chills, muscle aches, diarrhea, and rash. This bacterium is the principal cause of many pneumonias in the summer and fall months, and the condition often referred to as "atypical pneumonia." Macrolides (erythromycin, clarithromycin, azithromycin, and fluoroquinolones) are antibiotics commonly prescribed to treat Mycoplasma pneumonia. Legionnaire's disease is caused by the bacterium Legionella pneumoniae that is most often found in contaminated water supplies and air conditioners. It is a potentially fatal infection if not accurately diagnosed. Pneumonia is part of the overall infection, and symptoms include high fever, a relatively slow heart rate, diarrhea, nausea, vomiting, and chest pain. Older men, smokers, and people whose immune systems are suppressed are at higher risk of developing Legionnaire's disease. Fluoroquinolones (see above) are the treatment of choice in this infection. This infection is often diagnosed by a special urine test looking for specific antibodies to the specific organism. Mycoplasma, Legionnaire's, and another infection, Chlamydia pneumoniae, all cause a syndrome known as "atypical pneumonia." In this syndrome, the chest X-ray shows diffuse abnormalities, yet the patient does not appear severely ill. In the past, this condition was referred to as "walking pneumonia," a term that is rarely used today. These infections are very difficult to distinguish clinically and often require laboratory evidence for confirmation. Recently, a study performed in the Netherlands demonstrated that adding a steroid medication, dexamethasone (Decadron), to antibiotic therapy shortens the duration of hospitalization. This medication should be used with caution in patients whom are critically ill or already have a compromised immune system. Pneumocystis carinii (now known as Pneumocystis jiroveci) pneumonia is another form of pneumonia that usually involves both lungs. It is seen in patients with a compromised immune system, either from chemotherapy for cancer, HIV/AIDS, and those treated with TNF (tumor necrosis factor), such as for rheumatoid arthritis. Once diagnosed, it usually responds well to sulfa-containing antibiotics. Steroids are often additionally used in more severe cases. Viral pneumonias do not typically respond to antibiotic treatment. These infections can be caused by adenoviruses, rhinovirus, influenza virus (flu), respiratory syncytial virus (RSV), and parainfluenza virus (that also causes croup). These pneumonias usually resolve over time with the body's immune system fighting off the infection. It is important to make sure that a bacterial pneumonia does not secondarily develop. If it does, then the bacterial pneumonia is treated with appropriate antibiotics. In some situations, antiviral therapy is helpful in treating these conditions. More recently, H1N1, swine-origin influenza A, has been associated with very severe pneumonia often resulting in respiratory failure. This disease often requires the use of mechanical ventilation for breathing support. Death is not uncommon when this infection involves the lungs. Fungal infections that can lead to pneumonia include histoplasmosis, coccidiomycosis, blastomycosis, aspergillosis, and cryptococcosis. These are responsible for a relatively small percentage of pneumonias in the United States. Each fungus has specific antibiotic treatments, among which are amphotericin B, fluconazole (Diflucan), penicillin, and sulfonamides.