CHRONIC BACTERIAL DISEASE
Chronic bacterial infections persist for prolonged periods of time (e.g., months, years) in the host. This lengthy persistence is due to a number of factors including masking of the bacteria from the immune system, invasion of host cells, and the establishment of an infection that is resistance to antibacterial agents.
Over the past three decades, a number of chromic bacterial infections have been shown to be associated with the development of the adherent, exopolysaccharide-encased populations that are termed biofilms. The constituents of the exopolysaccharide are poorly immunogenic. This means that the immune system does not readily recognize the exopolysaccharide as foreign material that must be cleared from the body. Within the blanket of polysaccharide the bacteria, which would otherwise be swiftly detected by the immune system, are protected from immune recognition. As a result, the infection that is established can persist for a long time.
An example of a chronic, biofilm-related bacterial infection is prostatitis. Prostatitis is an inflammation of the prostate gland that is common in men over 30 years of age. Symptoms of this disease can include intense pain, urinary complications, and sexual malfunction including infertility. Chronic bacterial prostatitis is generally associated with repeated urinary tract infections. The chronic infection is typically caused by biofilms of Escherichia coli.
A second biofilm-related chronic bacterial infection is the Pseudomonas aeruginosa lung infection that develops early in life in some people who are afflicted with cystic fibrosis. Cystic fibrosis is due to a genetic defect that restricts the movement of salt and water in and out of cells in the lung. The resulting build-up of mucus predisposes the lungs to bacterial infection. The resulting Pseudomonas aeruginosa infection becomes virtually impossible to clear, due the antibiotic resistance of the bacteria within the biofilm. Furthermore, the body's response to the chronic infection includes inflammation. Over time, the inflammatory response is causes breathing difficulty that can be so pronounced as to be fatal.
Another chronic bacterial infection that affects the lungs is tuberculosis. This disease causes more deaths than any other infectious disease. Nearly two billion people are infected with the agent of tuberculosis, the bacterium Mycobacterium tuberculosis. As with other chronic infections, the symptoms can be mild. But, for those with a weakened immune system the disease can become more severe. Each year some three million people die of this active form of the tuberculosis infection.
Tuberculosis has re-emerged as a health problem in the United States, particularly among the poor. The development of drug resistance by the bacteria is a factor in this reemergence.
Beginning in the mid 1970s, there has been an increasing recognition that maladies that were previously thought to be due to genetic or environmental factors in fact have their basis in chronic bacterial infections. A key discovery that prompted this shift in thinking concerning the origin of certain diseases was the demonstration by Barry Marshall that a bacterium called Helicobacter pylori is the major cause of stomach ulcers. Furthermore, there is now firm evidence of an association with chronic Helicobacter pylori stomach and intestinal infections and the development of certain types of intestinal cancers.
At about the same time the bacterium called Borrelia burgdorferi was established to be the cause of a debilitating disease known as Lyme disease. The spirochaete is able to establish a chronic infection in a host. The infection and the host's response to the infection, causes arthritis and long-lasting lethargy.
As a final recent example, Joseph Penninger has shown that the bacterium Chlamydia trachomatis is the agent that causes a common form of heart disease. The bacterium chronically infects a host and produces a protein that is very similar in three-dimensional structure to a protein that composed a heart valve. The host's immune response to the bacterial protein results in the deterioration of the heart protein, leading to heart damage.
Evidence is accumulating that implicates chronic bacterial infection with other human ailments including schizophrenia
and Alzheimer's disease. While not yet conclusive, the involvement of chronic bacterial infections in maladies that have hitherto not been suspected of having a bacterial origin will not be surprising.
Research efforts to prevent chronic bacterial infections are focusing on the prevention of the surface adhesion that is a hallmark of many such infections. Molecules that can competitively block the sites to which the disease-causing bacteria bind have shown promising results in preventing infections in the laboratory setting.
