Bacteria

Bacteria is a one-celled organisms visible only through a microscope. Bacteria live all around us and within us. The air is filled with bacteria, and they have even entered outer space in spacecraft. Bacteria live in the deepest parts of the ocean and deep within Earth. They are in the soil, in our food, and on plants and animals. Even our bodies are home to many different kinds of bacteria. Our lives are closely intertwined with theirs, and the health of our planet depends very much on their activities.

Bacterial cells are so small that scientists measure them in units called micrometers (µm). One micrometer equals a millionth of a meter (0.0000001 m or about 0.000039 in), and an average bacterium is about one micrometer long. Hundreds of thousands of bacteria would fit on a rounded dot made by a pencil.

Bacteria lack a true nucleus, a feature that distinguishes them from plant and animal cells. In plants and animals the saclike nucleus carries genetic material in the form of deoxyribonucleic acid (DNA). Bacteria also have DNA but it floats within the cell, usually in a loop or coil. A tough but resilient protective shell surrounds the bacterial cell.

Biologists classify all life forms as either prokaryotes or eukaryotes. Prokaryotes are simple, single-celled organisms like bacteria. They lack a defined nucleus of the sort found in plant and animal cells. More complex organisms, including all plants and animals, whose cells have a nucleus, belong to the group called eukaryotes. The word prokaryote comes from Greek words meaning “before nucleus”; eukaryote comes from Greek words for “true nucleus.”

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.