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Nonmotile Gram-positive facultative anaerobic cocci (see WebLinked image; see WebLinked image; see WebLinked image)
Microscopically cells occur singly and in pairs, short chains, and grape-like clusters
Both respiratory and fermentative metabolism; Nitrate often reduced to nitrite
Capsule or slime layer (diffuse capsule) may be present more commonly in vivo; Particularly important in Staphylococcus epidermidis colonization
Cell wall contains teichoic acid
Ribitol teichoic acid (Polysaccharide A) in Staphylococcus aureus
Glycerol teichoic acid (Polysaccharide B) in S. epidermidis
Enzymes:
Protein A
Uniformly coats surface of S. aureus
Not present on coagulase-negative staphylococci
S. aureus ferments mannitol; Most other staphyloccocci are mannitol negative
Halotolerant (grow in medium containing < 10% NaCl); Salt is useful as a selective constituent in isolation media
Wide temperature range for growth (18oC - 40oC)
Staphylococcal strains vary in pigmentation and susceptibility to antibiotics
S. epidermidis and other coagulase-negative staphylococci:Cutaneous Infections:
Furuncles (boils)
Impetigo
- Bullous impetigo
- Pustular impetigo
Wound infections
Scalded skin syndrome: neonates and children under the age of four
Toxic-shock syndrome
Food poisoning
Other infections:
Pneumonia
- Empyema
Bacteremia (hospital-acquired)
Osteomyelitis: disease of growing bone
Septic arthritis
Septic embolization
Metastatic infections
Staphylococcus saprophyticus:Endocarditis: infections of either native or artificial heart valves
Catheter and shunt infections
Prosthetic joint infections
Other opportunistic infections
Urinary tract infections in sexually active young women
Staphylococci are common flora: skin, nasal cavity, oropharynx, gastrointestinal tract, genitourinary tract
Transient colonization by S. aureus
Transmission by direct contact or by fomite
Carrier state: short or long-term, often colonizing the anterior nares
Nosocomial infections
Somatic virulence factors:Enzymes:
Coagulases:
- bound (clumping factor)
- free (coagulase-reacting factor)
Hyaluronidase: "spreading factor" of S. aureus
Nucleases: S. aureus; Cleaves DNA (DNase) and RNA (RNase)
Fibrinolysin: staphylokinase
Lipases: esterases
Penicillinase
Exotoxins:
Cytotoxins (hemolysins): cytopathic and cytolytic for a broad range of affected cells, including erythrocytes, leukocytes, macrophages, hepatocytes, lymphocytes, lymphoblasts, fibroblasts, neutrophils and platelets
- Alpha toxin
- Beta toxin: sphingomyelinase C (phospholipase)
- Delta toxin: detergent-like activity
- Gamma toxin: hemolytic activity
- Leukocidin
Enterotoxins (A to E)
Exfoliative toxin (epidermolytic toxin or exfoliatin) (A and B)
Toxic shock syndrome toxin-1 (TSST-1) (formerly pyrogenic exotoxin C)
Slime layer (capsule)
Protein A: binds Fc receptors of IgG
Teichoic acid: binds fibronectin
Microscopy: gram reaction and morphology
Culture and biochemical confirmation
Serology
Drain infected area
Deep/metastatic infections: semi-synthetic penicillins; cephalosporins, erythromycin or clindamycin
Endocarditis: semi-synthetic penicillin plus an aminoglycoside
Carrier status prevents complete control
Proper hygiene, segregation of carriers from highly susceptible individuals
Good aseptic techniques when handling surgical instruments
Control of nosocomial infections
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