Chlamydophila pneumoniae, as the name suggests, usually causes a form of pneumonia. The organism used to be known as Chlamydia pneumoniae. It is a very small bacterium measuring between 0.2 to 1 micrometers. Like all members of the Chlamydiae, it is an obligate intracellular pathogen. This means it can only reproduce inside another cell.
C. pneumoniae causes respiratory diseases and has been implicated in sinusitis and bronchitis as well as pneumonia. The type of pneumonia it causes is generally known as atypical pneumonia.
Its life cycle involves two distinct forms. Outside of the host cell it exists as an elementary body while inside the cell it forms a reticulate body. While not active, biologically, the elementary body protects the organism from the environment allowing it to be spread from host to host.
Once the elementary body has been inhaled, it enters the lung where it is taken into a cell by phagocytosis. Within the cell, it is contained within an endosome. Normally lysosomes attack and destroy particles held within an endosome. C. pneumoniae resists the lysosomes attack to transform into an active reticulate body.
The reticulate body will replicate within the cell. To complete its replication C. pneumoniae hijacks some of its host cells replication equipment. In this, its life cycle resembles that of a virus.
Once replicated the reticulate bodies revert to elementary bodies to be released from the host cell. This often results in the death of the host cell. Once released the elementary bodies can infect further cells within the lung or be expelled by coughing to infect another person.
The symptoms of an infection caused by C. pneumoniae include fever, cough and difficulty in breathing. A chest X-ray may show discrete opaque patches but this is not always the case. It sometimes causes a walking pneumonia in that the patient is ambulatory and still able to function in some degree as opposed to being bed-bound.
The atypical pneumonia caused by C. pneumoniae cannot be distinguished from other forms of bacterial pneumonia by symptoms alone. A laboratory diagnosis is required to ensure the proper treatment of this condition.
It cannot be grown on routine bacterial media and its size makes it very difficult to visualize with regular microscopic methods, such as the Gram stain, used in a bacteriology laboratory. It can be detected, in clinical samples, by fluorescent microscopy using a labeled monoclonal antibody or by the polymerase chain reaction method. Diagnosis can also be made by looking for high or rising antibody levels to the organism in the patient’s blood.
C. pneumoniae infections respond well to antibiotic treatment although sometimes a prolonged course of therapy is required. The antibiotic of choice is doxycycline although it will respond to treatment with some macrolide antibiotics such as clarithromycin, which are useful in treating other causes of atypical pneumonia such as mycoplasma.
Very rarely has C. pneumoniae been found causing infections outside of the respiratory tract. However, occasional cases of meningo-encephalitis, myocarditis and infectious arthritis caused by this organism do occur.
There is evidence that it may be implicated some cases of myocardial infarction (heart attack). In that, many heart patients have high levels of anti C. pneumoniae antibody. The organism has also been isolated from plaques on the coronary artery walls in some patients. However, the treatment of heart patients who have high levels of antibodies to C. pneumoniae with an appropriate antibiotic does not lower the rate of repeat heart attacks. Whether they have the heart condition because of the organism or are more prone to infection because of the heart problem is up for debate.
