Staphylococcus
(staf‵ĭ-lō-kok'ŭs 
)
[Gr. staphylē, a bunch of grapes + coccus ]
A genus of micrococci belonging to the family Staphylococcaceae, order Bacillales. They are gram-positive and , when cultured on agar, produce white, yellow, or orange colonies. Some species are pathogenic, causing suppurative conditions and elaborating exotoxins destructive to tissues. Some produce enterotoxins and are the cause of a common type of food poisoning.
S. aureus A species that is coagulase positive, often part of resident flora of the skin and the nasal and oral cavities. These bacteria may cause suppurative conditions such as boils, carbuncles, abscesses, hospital-acquired infections, foreign body (prosthetic) infections, life-threatening pneumonia, or sepsis. Various strains of this species produce toxins, including those that cause food poisoning, staphylococcal scalded skin syndrome, and toxic shock syndrome. Some strains also produce hemolysins and staphylokinase.
methicillin-resistant S. aureus
ABBR: MRSA
A strain of S. aureus resistant to methicillin (and other beta-lactams). MRSA is a common cause of boils (skin abscesses) and an occasional cause of pneumonia. MRSA is resistant to most antibiotics and is usually acquired in hospitals or nursing homes, where it may be spread from patient to patient by contaminated hand s, clothing, and equipment.About 0.5% of people in the U.S. harbor MRSA on their skin or in their noses and , although colonized but not infected, can still spread the bacteria to those at risk. The Centers for Disease Control and Prevention (CDC) estimates that about 17,000 people die from MRSA infection each year.
Antibiotic resistance develops from the selection pressure exerted on bacteria by excessive use of antibiotics, e.g., in animal husband ry or in medical practices.
Patients usually develop one or more painful, dome-shaped, inflamed boils on the skin. Patients with pneumonia typically have cough, sputum production, fevers, and /or pleurisy.
The diagnosis is confirmed by microbiological culture and sensitivity of exudate from an abscess or sputum but is often suspected when a cluster of furuncles is found on the skin.
Sulfa drugs and clindamycin effectively treat MRSA when given orally or intravenously. Topical antiseptics, such as chlorhexidine gluconate, are also applied to the skin of patients to kill bacteria.
The CDC suggests screening high-risk patients (such as those with weak immune systems, intensive care patients, and patients in nursing homes), rather than recommending universal screening for all hospitalized patients. In addition to screening, agencies may provide MRSA carriers with special soap and antibiotic nasal creams. Contact isolation procedures, scrupulous hand washing, and hospital disinfection practices are all used.
SEE: isolation; antibiotic resistance .
vancomycin-resistant S. aureus
ABBR: VRSA
A strain of S. aureus resistant to vancomycin that may become a serious nosocomial pathogen. Strains with intermediate resistance to vancomycin have caused life-threatening infections.S. capitis A coagulase-negative Staphylococcus species that has been isolated from infections in premature neonates and patients with endocarditis.
S. caprae A coagulase-negative, DNAse-positive Staphylococcus species first identified in goats. It can infect humans, e.g., in prosthetic joints and injured bones.
S. epidermidis A coagulase-negative species that is part of the normal flora of the skin. It may colonize, form biofilms on, and infect prosthetic devices and indwelling catheters.
S. haemolyticus A coagulase-negative Staphylococcus species that primarily infects premature neonates and patients being treated for cancer or other immune-suppressing conditions. The species can also cause meningitis; infections of the skin, soft tissue, or prosthetic joints; or bacteremia. It is frequently resistant to multiple common antibiotics.
S. hominis A coagulase-negative species frequently recovered from skin. It is not consistently pathogenic for humans.
S. lugdunensis An aggressive coagulase-negative Staphyloccus species. It causes infections of soft tissues, the bloodstream, and prostheses.
S. saprophyticus A species that is the second most common cause of urinary tract infection in young, sexually active females. It is a rare cause of pneumonia.