Streptomycin

Streptomycin, antibiotic agent produced by a filamentous (thready) soil bacterium, Streptomyces griseus. Microorganisms that cause many serious diseases, such as tuberculosis, leprosy, and cholera, are susceptible to streptomycin. The first drug effective against tuberculosis, it is still used for this condition, although it has been replaced for most purposes by newer, more effective antibiotics of the same chemical family, the aminoglycosides. These include gentamicin, tobramycin, amikacin, and kanamycin.

An important drawback to the use of streptomycin is the development of resistance to the drug by certain bacteria. Resistance may be delayed by supplementing streptomycin with para-aminosalicylic acid or isoniazid. Streptomycin occasionally causes damage to the vestibular or auditory division of the eighth cranial nerve. Aminoglycosides may also damage the kidney.

Tuberculosis

Tuberculosis (TB), chronic or acute bacterial infection that primarily attacks the lungs, but which may also affect the kidneys, bones, lymph nodes, and brain. The disease is caused by Mycobacterium tuberculosis, a rod-shaped bacterium. Symptoms of TB include coughing, chest pain, shortness of breath, loss of appetite, weight loss, fever, chills, and fatigue. Children and people with weakened immune systems are the most susceptible to TB. Half of all untreated TB cases are fatal.

TB is transmitted from person to person, usually by inhaling bacteria-carrying air droplets. When a person sick with TB coughs, sneezes, or speaks, small particles that carry two to three bacteria surrounded by a layer of moisture are released in the air. When another person inhales these particles, the bacteria may lodge in that person’s lungs and multiply.

Diagnosis of TB requires two separate methods. Tuberculin skin testing is a method of screening for exposure to TB infection. A person who was infected with TB will have developed a hypersensitivity to the TB bacteria even if they did not develop the disease. A purified protein derived from the bacteria is injected into the skin. The skin area is inspected 48 to 72 hours later for a bump. A positive test implies that TB infection has occurred. Skin tests are not 100 percent accurate and they do not always indicate the presence of active disease.

General preventive measures can be taken to reduce the spread of TB in public places. Ventilation systems lessen the chance of infection by dispersing the bacteria. Ultraviolet lighting also reduces, but does not eliminate, the threat of infection by killing TB bacteria in confined spaces. Vaccines, such as the bacillus Calmette Guerin (BCG) vaccine, prepared from bacteria that have been weakened, are another preventive measure. The BCG vaccine is most effective in preventing childhood cases of TB.

With the advent of effective antibiotics for TB, drug therapy has become the cornerstone of treatment. Single-drug treatment often causes bacterial resistance to drugs. Therefore, all recommended therapies include multiple drugs given for at least 6 months, often for as long as 9 to 12 months. Adjustments to the treatments are made based on susceptibility of the bacterial strain. A combination of antibiotics, including isoniazid, rifampin, streptomycin, pyrazinamide, and ethambutol, is usually prescribed.

Antibiotics

Antibiotics (Greek anti, “against”; bios, “life”) are chemical compounds used to kill or inhibit the growth of infectious organisms. Originally the term antibiotic referred only to organic compounds, produced by bacteria or molds, that are toxic to other microorganisms. The term is now used loosely to include synthetic and semisynthetic organic compounds. Antibiotic refers generally to antibacterials; however, because the term is loosely defined, it is preferable to specify compounds as being antimalarials, antivirals, or antiprotozoals. All antibiotics share the property of selective toxicity: They are more toxic to an invading organism than they are to an animal or human host. Penicillin is the most well-known antibiotic and has been used to fight many infectious diseases, including syphilis, gonorrhea, tetanus, and scarlet fever. Another antibiotic, streptomycin, has been used to combat tuberculosis.

Leprosy

Leprosy or Hansen's Disease is a chronic infectious disease caused by the bacterium Mycobacterium leprae. Leprosy can be treated effectively with several drugs, but if left untreated, the disease can result in severe disfigurement, especially of the feet, hands, and face. It is rarely fatal.

Leprosy has long been one of the most feared diseases worldwide. The stigma attached to leprosy has often caused those who contracted the disease to be shunned by family, friends, and society.

Leprosy has two main forms, known as tuberculoid and lepromatous disease. In tuberculoid leprosy, the skin lesions are few and small, with only a few bacteria present in each. In lepromatous leprosy, the more severe form of the disease, the lesions may be much more widespread and contain many leprosy bacteria. As lepromatous leprosy progresses, hard nodules and folds of skin may form on the face and the nose may collapse, giving a person a characteristic lionlike appearance.

The symptoms of leprosy may be caused by proliferation of the bacteria in lepromatous leprosy or by the body’s immune response to the bacteria in tuberculoid leprosy. In both forms of leprosy, there is usually some degree of irreversible nerve damage resulting from either of these two processes. Because of the lack of sensation in affected areas of the skin, people with leprosy often do not notice burns and injuries to their fingers and toes and fail to treat them. These injuries can then become infected with other types of bacteria that cause tissue damage. Gradually, damaged tissue and bone are resorbed by the body, causing the digits to become shorter. However, leprosy does not, as myth would have it, cause parts of the body to fall off. Damage to nerves in the hands and feet may also cause the fingers and toes to become stiff and curl inward, and some patients become unable to walk. Both forms of the disease may also lead to blindness.

The first effective drug for treating leprosy, called promin, was developed in the mid-1940s. Within several years, painful daily promin injections were replaced with oral doses of a related drug, called dapsone. By the early 1980s, strains of the leprosy bacterium resistant to dapsone had become widespread, and multidrug therapy, a combination of several medications, became necessary to treat the disease. Three antibiotics, dapsone, rifampin, and clofazimine, are currently used to treat leprosy. The drugs must be taken for a long period, typically six months in cases of tuberculoid leprosy and two years for lepromatous leprosy. Treating leprosy using multidrug therapy is much more effective than using any one drug alone, and this treatment helps ensure that a drug-resistant form of the leprosy bacterium will not develop. These drugs cannot reverse the nerve damage and deformities of the hands, feet, and face that are characteristic of the disease. However, they can often halt the progression of the disease and help prevent it from being passed on to anyone else.

Cholera

Cholera, severe infectious disease endemic in India and some other tropical countries and occasionally spreading to temperate climates. The symptoms of cholera are diarrhea and the loss of water and salts in the stool. In severe cholera, the patient develops violent diarrhea with characteristic “rice-water stools,” vomiting, thirst, muscle cramps, and sometimes circulatory collapse. Death can occur as quickly as a few hours after the onset of symptoms. The mortality rate is more than 50 percent in untreated cases, but falls to less than 1 percent with proper treatment.

Treatment consists mainly of intravenous or oral replacement of fluids and salts. Packets for dilution containing the correct mixture of sodium, potassium, chloride, bicarbonate, and glucose have been made widely available by the WHO. Most patients recover in three to six days. Antibiotics such as tetracyclines, ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole can shorten the duration of the disease.

A vaccine made from killed bacteria is commercially available and offers partial protection for a period of three to six months after immunization. Experimental studies have shown that the cholera bacterium produces a toxin that causes the small intestine to secrete large amounts of fluid, which leads to the fluid loss characteristic of the disease. This has led to work on a vaccine containing inactivated toxin. Attempts are also being made to develop a vaccine containing live bacteria that have been altered so that they do not produce the toxin.