BSCI 424 Pathogenic Microbiology -- Staphylococcus

BSCI 424 — PATHOGENIC MICROBIOLOGY — Fall 2000

Staphylococcus Summary

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Morphology and Physiology:

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:

Strongly catalase positive

Differentiates staphyloccoci from streptococci

Coagulase

S. aureus is coagulase positive

Both free and bound coagulase
Bound coagulase = clumping factor

All other staphyloccocci are coagulase negative

Usually oxidase negative

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 (18^oC - 40^oC)

Staphylococcal strains vary in pigmentation and susceptibility to antibiotics

Clinical Syndromes:

S. aureus:

  Cutaneous Infections:

  Folliculitis

  Furuncles (boils)

  Carbuncles

  Impetigo
  Bullous impetigo

  Pustular impetigo

   Wound infections

  Toxin-Mediated Infections:

  Scalded skin syndrome: neonates and children under the age of four

  Toxic-shock syndrome

  Food poisoning

  Other infections:

  Pneumonia
  Empyema

  Bacteremia (hospital-acquired)

  Endocarditis

  Osteomyelitis: disease of growing bone

  Septic arthritis

  Septic embolization

  Metastatic infections

S. epidermidis and other coagulase-negative staphylococci:

  Endocarditis: infections of either native or artificial heart valves

  Catheter and shunt infections

  Prosthetic joint infections

  Other opportunistic infections

Staphylococcus saprophyticus:

  Urinary tract infections in sexually active young women

  Dysuria

  Pyuria

Epidemiology:

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

Endemic and epidemic disease

Nosocomial infections

Pathogenesis:

Extracellular 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)

Somatic virulence factors:

  Slime layer (capsule)

  Protein A: binds Fc receptors of IgG

  Teichoic acid: binds fibronectin

Laboratory Identification:

Microscopy: gram reaction and morphology

Culture and biochemical confirmation

Serology

Treatment and Prevention:

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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