Advances in Mycobacterial Genetics: New Promises for Old Diseases

Historically, members of the genus Mycobacterium have been some of the most important players in the drama of infectious disease and immunology of man.Mycobacterium leprae causes leprosy, a disease that dates back to biblical times and continues to afflict millions around the world today.M.leprae was discovered by G.A.HANSEN in 1873 and found to be the first bacteria associated with human disease.Despite this early discovery, this bacillus has yet to be cultivated on artificial media and can only be propagated in the laboratory in nine-banded armadillos or footpads of mice.Twenty years ago, tuberculosis was thought to be a disease that was no longer to be a menace in the world with the presence of a vaccine and the development of effective chemotherapies to control this infection.However, in the last five years the world has seen alarming resurgence of tuberculosis.The World Health Organization estimates that there are 8 million new cases of tuberculosis and 3 million deaths resulting from this dreaded illness every year.An increasing number of reports of infections with drug-resistant Mycobacterium tuberculosis cells makes this resurgence so much more frightening.Since the introduction of isoniazid in 1954,.the United States had thirty-two years of steady decline of the number of new cases of tuberculosis.This trend ended in 1986 and we have seen steady increases with a 5 % increase in 1989 alone.This increase is most likely a result of the epidemic of the Acquired Immunodeficiency Syndrome (AIDS), where M.tuberculosis infection appears to be one of the first signs of a loss of T cell function.AIDS patients also have a number of opportunistic infections, including infections by another mycobacterium, Mycobacterium avium.This bacterium rarely causes disease in immunocompetent individuals and yet is being found in greater than 40 of AIDS patients in the US.Infections caused by M.avium are difficult to treat as the bacterium appears to be refractory to existing chemotherapies.It is quite clear that all of these mycobacteria continue to be significant cause of morbidity and mortality in man.