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Related to coagulase-positive staphylococcus: Staphylococcus aureus, Staphylococcus intermedius


(stăf'ələkŏk`əs), any of the pathogenic bacteriabacteria
[pl. of bacterium], microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles. Once considered a part of the plant kingdom, bacteria were eventually placed in a separate kingdom, Monera.
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, parasitic to humans, that belong to the genus Staphylococcus. The spherical bacterial cells (cocci) typically occur in irregular clusters [Gr. staphyle=bunch of grapes]. The term staphylococcus is also sometimes used loosely for the cluster arrangement itself and, broadly, for any bacteria with such a growth pattern. The pigments produced by staphylococci are the basis of the names given to the various strains—those with colors ranging from orange to yellow are designated S. aureus; white strains are known as S. albus.

Staphylococci cause abscesses, boils, and other infections of the skin, such as impetigoimpetigo
, contagious skin infection affecting mainly infants and children. The causative organisms are either hemolytic streptococci or staphylococci. The eruption consists of small red spots or blisters that rupture, discharge, and become encrusted.
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. They can also produce infection in any organ of the body (e.g., staphylococcal pneumonia of the lungs). The most common form of food poisoningfood poisoning,
acute illness following the eating of foods contaminated by bacteria, bacterial toxins, natural poisons, or harmful chemical substances. It was once customary to classify all such illnesses as "ptomaine poisoning," but it was later discovered that ptomaines, the
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 is brought on by staphylococcus-contaminated food. The staphylococcus organisms also generate toxins and enzymes that can destroy both red and white blood cells.

Unlike some other types of bacteria, staphylococci are generally partly or wholly resistant to antibiotic action; this raises serious problems in the treatment and control of staphylococcus infections (see drug resistancedrug resistance,
condition in which infecting bacteria can resist the destructive effects of drugs such as antibiotics and sulfa drugs. Drug resistance has become a serious public health problem, since many disease-causing bacteria are no longer susceptible to previously
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). The rise of drug-resistant virulent strains of S. aureus, particularly methicillin-resistant S. aureus (MRSA), has led increasing concern in the medical community. Although sick patients with compromised immune systems and children are most susceptible to the strains, which most typically are contracted in hospital, nursing home, and other health-care settings, healthy persons have also been infected. Pharmaceutical companies are working to develop new antibiotics to kill drug-resistant strains of staphylococcus and other bacteria, and a vaccine for S. aureus has been developed.


A genus of bacteria containing at least 28 species that are collectively referred to as staphylococci. Their usual habitat is animal skin and mucosal surfaces. Although the genus is known for the ability of some species to cause infectious diseases, many species rarely cause infections. Pathogenic staphylococci are usually opportunists and cause illness only in compromised hosts. Staphylococcus aureus, the most pathogenic species, is usually identified by its ability to produce coagulase (proteins that affect fibrinogen of the blood-clotting cascade). Since most other species of staphylococci do not produce coagulase, it is useful to divide staphylococci into coagulase-positive and coagulase-negative species. Coagulase-negative staphylococci are not highly virulent but are an important cause of infections in certain high-risk groups. Although Staphylococcus infections were once readily treatable with antibiotics, some strains have acquired genes making them resistant to multiple antimicrobial agents. See Bacteria, Drug resistance, Medical bacteriology

Staphylococcus cells are spherical with a diameter of 0.5–1.5 micrometers. Clumps of staphylococci resemble bunches of grapes when viewed with a microscope, owing to cell division in multiple planes. The staphylococci have a gram-positive cell composition, with a unique peptidoglycan structure that is highly cross-linked with bridges of amino acids. See Stain (microbiology)

Most species are facultative anaerobes. Within a single species, there is a high degree of strain variation in nutritional requirements. Staphylococci are quite resistant to desiccation and high-osmotic conditions. These properties facilitate their survival in the environment, growth in food, and communicability.

In addition to genetic information on the chromosome, pathogenic staphylococci often contain accessory elements such as plasmids, bacteriophages, pathogenicity islands (DNA clusters containing genes associated with pathogenesis), and transposons. These elements harbor genes that encode toxins or resistance to antimicrobial agents and may be transferred to other strains. Genes involved in virulence, especially those coding for exotoxins and surface-binding proteins, are coordinately or simultaneously regulated by loci on the chromosome. See Bacterial genetics, Bacteriophage, Plasmid, Transposons

Most Staphylococcus aureus infections develop into a pyogenic (pus-forming) lesion caused by acute inflammation. Inflammation helps eliminate the bacteria but also damages tissue at the site of infection. Typical pyogenic lesions are abscesses with purulent centers containing leukocytes, fluid, and bacteria. Pyogenic infections can occur anywhere in the body. Blood infections (septicemia) can disseminate the organism throughout the body and abscesses can form internally.

Certain strains of S. aureus produce exotoxins that mediate two illnesses, toxic shock syndrome and staphylococcal scalded skin syndrome. In both diseases, exotoxins are produced during an infection, diffuse from the site of infection, and are carried by the blood (toxemia) to other sites of the body, causing symptoms to develop at sites distant from the infection. Toxic shock syndrome is an acute life-threatening illness mediated by staphylococcal superantigen exotoxins. Staphylococcal scalded skin syndrome, also known as Ritter's disease, refers to several staphylococcal toxigenic infections. It is characterized by dermatologic abnormalities caused by two related exotoxins, the type A and B exfoliative (epidermolytic) toxins. See Cellular immunology, Toxic shock syndrome

Staphylococcal food poisoning is not an infection, but an intoxication that results from ingestion of staphylococcal enterotoxins in food. The enterotoxins are produced when food contaminated with S. aureus is improperly stored under conditions that allow the bacteria to grow. Although contamination can originate from animals or the environment, food preparers with poor hygiene are the usual source. Effective methods for preventing staphylococcal food poisoning are aimed at eliminating contamination through common hygiene practices, such as wearing gloves, and proper food storage to minimize toxin production. See Food poisoning

Coagulase-positive staphylococci are the most important Staphylococcus pathogens for animals. Certain diseases of pets and farm animals are very prominent. Staphylococcus aureus is the leading cause of infectious mastitis in dairy animals.



a genus of spherical bacteria. Staphylococcal cells, which are 0.6–0.8 microns in diameter, do not form spores. They are gram-positive and nonmotile and reproduce by dividing in various planes. The newly formed cells remain joined, forming masses similar to a bunch of grapes; they may also occur singly and in pairs. Staphylococci grow well on plain agar and potatoes. Certain species can ferment a variety of carbohydrates and alcohols to form acids. Staphylococci can also produce many toxic products, including hemolysin, which dissolves human erythrocytes; leukocidin, which dissolves leukocytes; and plasmin, which dissolves fibrin clots. Staphylococci are pathogenic, since they cause the suppuration of wounds and give rise to abscesses, furuncles, tonsillitis, inflammatory skin diseases, and septic conditions. Staphylococcus aureus, which produces enterotoxin, may cause severe food poisoning. Staphylococci are present in pus, the surface of healthy skin and mucous membranes, and room dust.