Staphylococcus

Staphylococcus, genus of round, parasitic bacteria, commonly found in air and water and on the skin and upper part of the human pharynx. These bacteria are known to cause pneumonia and septicemia as well as boils and kidney and wound infections (see Abscess; Carbuncle; Infection). The antibiotic drug penicillin was once effective for the treatment and control of staphylococci, but the increase of resistant strains requires use of other antiobiotic agents such as semi-synthetic penicillins, cephalosporins or vancomycin. Two common species of Staphylococcus include Staphylococcus aureus, which is commonly responsible for skin infections, and Staphylococcus epidermis, which does not normally cause infection. However, either of these bacteria can cause serious infections under the right conditions.

S. aureus is found on the skin and in the nostrils of many healthy individuals. These bacteria often give rise to minor superficial diseases, including the formation of pustules or boils in hair follicles. S. aureus infections are characterized by the presence of pus and formation of abscesses. In addition to skin pustules, boils, and carbuncles, S. aureus is responsible for impetigo, infections of wounds and burns (particularly in a hospital environment), breast abscesses, whitlow (inflammation of a finger or toe near the nail), osteomyelitis, bronchopneumonia, septicemia, acute endocarditis, food poisoning, and scalded skin syndrome. Scalded skin syndrome occurs in newborns and is due to infection by toxigenic strains of S. aureus. The toxins cause the skin to exfoliate, which leaves an appearance of having been scalded.

S. epidermis does not usually cause infection, occurring universally in a harmless symbiotic relationship (see Symbiosis). It is usually present on most areas of the skin, in the nostrils, mouth, external ear, and urethra. However, S. epidermis can take advantage of a host with a suppressed immune system and can aggravate an existing condition. Following heart surgery, S. epidermis may cause endocarditis. S. epidermis may turn an existing abnormality in the urinary tract into cystitis.

Penicillin

Penicillin acts both by killing bacteria and by inhibiting their growth. It does not kill organisms in the resting stage but only those growing and reproducing. Penicillin is effective against a wide range of disease-bearing microorganisms, including pneumococci, streptococci, gonococci, meningococci, the clostridium that cause tetanus, and the syphilis spirochete. The drug has been successfully used to treat such deadly diseases as endocarditis, septicemia, gas gangrene, gonorrhea, and scarlet fever.

SEMISYNTHETIC PENICILLIN

Despite the effectiveness of penicillin in curing a wide range of diseases, infections caused by certain strains of staphylococci cannot be cured by the antibiotic because the organism produces an enzyme, penicillinase, capable of destroying the antibiotic. In addition, enterococci and other bacteria known to cause respiratory and urinary tract infections were found intrinsically resistant to the action of penicillin. Appropriate chemical treatment of a biological precursor to penicillin, isolated from bacterial cultures, resulted in the formation of a number of so-called semisynthetic penicillins. The most important of these are methicillin and ampicillin—the former is remarkably effective against penicillinase-producing staphylococci and the latter is not only active against all organisms normally killed by penicillin, but also inhibits enterococci and many other bacteria.

DOSAGES

The strength and dosage of penicillin are measured in terms of international units. Each of these units is equal to 0.0006 g of the crystalline fraction of penicillin called penicillin G. In the early days of penicillin therapy, the drug was administered every three hours in small doses. More recently, a preparation called benzathine penicillin G has been produced that provides detectable levels of antibiotic for as long as four weeks after a single intramuscular injection; it is useful for treatment of syphilis and strep throat. Bacterial resistance to some penicillins has increased over the years, creating a need for alternative therapies.

Endocarditis

Endocarditis, infection and inflammation of the membrane lining the inner surface of the heart, including the heart valves. The two major forms of the disease are the acute type, which appears suddenly and can be fatal within a few days, and the subacute type, which develops slowly and may cause death within months. Many cases of the acute form are caused by the bacterium Staphylococcus aureus; the subacute form is often due to infection by streptococcal bacteria. Either type can result from fungus infections.

Subacute bacterial endocarditis usually results in fever, toxemia, and lesions of the heart valves; particles dislodged from these lesions often cause embolism. Infection of the heart valves and lining, or endocardium, may come from primary infections of the teeth, tonsils, and sinuses. The disease is characterized by the formation of bacterial or fungal growths on the valves and endocardium. It has its greatest incidence in people between the ages of 30 and 50 years. Antibiotic therapy, when used in large doses for extended periods, is effective in curing the bacterial infection of subacute bacterial endocarditis, but damage done to the heart by the bacteria cannot be repaired. Routine use of penicillin and other antibiotics during dental surgery and to treat primary bacterial infections has decreased the incidence of endocarditis.

Rheumatic Fever

Rheumatic Fever, once common acute inflammatory disease, characterized by fever and pain, tenderness, redness, and swelling of the joints. Rheumatic fever can cause inflammation of the heart and damage to the heart valves (Endocarditis). First attacks usually occur from the age of 7 to 12 or 14; recurrent attacks can occur throughout adult life. The mortality from the acute attack is low, and most cases subside spontaneously. Often, however, inflammation of the heart leads to scarring and deformity, causing the valves to malfunction. This strain on the heart muscle causes rheumatic heart disease, which can cause death in middle or later life.

Acute rheumatic fever is a complication of streptococcal infection, such as strep throat, scarlet fever, or erysipelas. It sometimes develops after infections so mild as to pass unnoticed. Rheumatic fever begins either insidiously or abruptly after a latent period of two to six weeks following the streptococcal infection. Aside from fever, malaise, and migratory arthritis, patients may develop nodules under the skin, skin rashes, abdominal pain, pleurisy, and chorea. The most serious aspect of the disease, however, is the involvement of the heart (carditis).

Treatment involves the use of penicillin to eradicate streptococci that may still be present, bed rest, and administration of salicylates or corticosteroids. It may take many weeks or months before the attack runs its course. Rheumatic fever has become relatively rare, probably due at least in part to the widespread use of antibiotics.

Scarlet Fever

Scarlet Fever, infectious disease, caused by group A hemolytic streptococci, which also causes strep throat. The causative organism usually enters the body through the nose or mouth; it is transmitted from person to person by direct contact, that is, by sprays of droplets from the respiratory tract of an infected person, or by indirect contact through the use of utensils previously handled by an infected person. The disease most commonly affects children between the ages of two and ten.

The typical initial symptoms of the disease are headache, sore throat, chills, fever, and general malaise. From two to three days after the first appearance of symptoms, red spots may appear on the palate; bright red papilla emerge on the tongue, giving it an appearance commonly called strawberry tongue. A characteristic skin eruption appears on the chest and usually spreads over the entire body except the face. The rash fades on pressure. The fever, which frequently runs as high as 40° to 40.6° C (104° to 105° F), generally lasts only a few days but may extend to a week or longer. The rash usually fades in approximately a week, and at that time the skin begins to peel.

Scarlet fever may be complicated by an infection of the middle ear mastoids or sinuses, or even by pneumonia. See also Rheumatic Fever. Occasionally, inflammation of the kidneys (glomerular nephritis) may develop after scarlet fever. Since the introduction of penicillin, however, most instances of scarlet fever can be cured without the occurrence of permanent aftereffects.