Infectious diseases can be a product of a number of environmental factors. Underlying any infectious disease is a causative infectious agent. The infectious agent typically is a pathogenic microorganism, for example, a pathogenic bacterium. The degree or ability of a pathogenic microorganism to overcome defense mechanisms and cause a disease is related to its virulence. Both pathogenic and nonpathogenic microorganisms are known to express cytotoxic factors, which allow the microorganism to defend itself from the host immune system and prevent phagocytes (e.g., macrophages and mast cells) from eliminating the microorganism from the body. When the pathogenic microorganisms survive, the microorganisms can invade the host tissues and proliferate, causing severe disease symptoms. Pathogenic bacteria have been identified as a root cause of a variety of debilitating or fatal diseases including, for example, tuberculosis, cholera, whooping cough, plague, and the like. To treat such severe infections, drugs, for example, antibiotics, are administered that either kill the infectious agent or disarm the cytotoxic factors so that the infectious agent is no longer able to defend itself against the host immune system. However, pathogenic bacteria commonly develop resistance to antibiotics and improved agents are needed to prevent the spread of infections due to such microorganisms.
A cancer is a malignant tumor of potentially unlimited growth. It is primarily the pathogenic replication (a loss of normal regulatory control) of various types of cells found in the human body. Initial treatment of the disease is often surgery, radiation treatment or the combination of these treatments, but locally recurrent and metastatic disease is frequent. Chemotherapeutic treatments for some cancers are available but these seldom induce long term regression. Hence, they are often not curative. Commonly, tumors and their metastases become refractory to chemotherapy, in an event known as the development of multidrug resistance. In many cases, tumors are inherently resistant to some classes of chemotherapeutic agents. In addition, such treatments threaten noncancerous cells, are stressful to the human body, and produce many side effects. Improved agents are therefore needed to prevent the spread of cancer cells.
Many cancers are known to regress when patients are infected with pathogenic bacteria. However, very little is known about how bacterial infections cause regression of human cancers.