Staph

Question 1

Staphylococcal Physiology and Characteristics

Answer 1

• Gram positive cocci (purple on stain)
• facultatively anaerobic
• form clusters
• rapid growth of sharply defined, smooth, opaque colonies on nonselevtive media
• catalase test = positive

Question 2

Staphylococcus aureus

Answer 2

Lab identification:

• beta-hemolytic on blood agar, yellowish tint
• slide coagulase test = usually positive
• tube coagulase test = positive
• particle agglutination test = positive
• Biochem test panel = Staph aureus

Toxin Virulence Factors:

• membrane- active toxins (lyses blood cells)
• Panton-Valentine leukocidin (PVL) (lyses leukocytes)
• Exfoliatin (disrupts integrity of epidermidis)
• Toxic shock syndrome toxin 1 (acts as superantigen causing massive cytokine release)
• enterotoxins A-E and G (induces V and D)

Epidemiology:

• lives on skin and on mucous membranes
• preferentially colonizes nares
  
  • about 1/4 of us have it in our nasal cavity

Infections:

• Localized infections:
  
  • Folliculitis = infection of one or more hair follicles
    
    • whether tx or not they will go away usually
  • Furuncles (boils) = skin infection involving the entire hair follicle and nearby skin tissue
    
    • folliculitis can progress to this
    • S: very painful
    • P/TX: usually need to be lanced and drained of pus
      
      • usually prescribe abx to discourage regrowth
      • usually resolve after drainage
  • Carbuncles - a skin infection that involves a group of hair follicles
    
    • when furuncles aren’s controlled
    • a lot of pressure builds up, a crack develops and pus spontaneously drains
    • at risk for disseminated staph infection where can get into bloodstream
  • Impetigo = highly contagious superficial skin infection
    
    • caused by strep pyogenes too
  • Cellulitis = infection and inflammation of dermal and subQ layers of skin
    
    • at risk for bacteremia
    • need antimicrobial tx
• Localized infections w/ Systemic Effects:
  
  • Scalded skin syndrome = Exfoliatin-mediated detachment of the granulosum and spinosum layers w/n epidermis
    
    • looks like a sunburn but peeling is much worse
  • Toxic shock syndrome = multi-system disease following “cytokine storm” induced by a staph toxin (TSST-1) (a superantigen)
    
    • cytokine diseases are of our own immune system
• Invasive Infections:
  
  • endocarditis = infection of inside lining of heart and hear valves (endocardium)
    
    • often w/ vegetation formation (big dark mass, inside is bacteria causing infection, much is fibrin and organisms inside that are continuing to grow and produce virulence factors that will destroy the heart valve)
  • pneumonia = infection of lung, usually involving the alveoli
    
    • air-fluid level seen in pleuritic infection
  • osteomyelitis = acute or chronic infection of bone
    
    • organism in bloodstream spreads to bone and lodges in it
    • can get erosion of bone
    • very painful
    • P/TX = need long term abx tx (because here is not really a rich blood supply so need more abx in order to get enough to the area to tx)
  • septic arthritis
• food poisoning

P/TX:

• PCNase resistant PCN, nafcillin (IV) and dicloxacillin (oral)
• 1st generation cephalosporins. cefazolin (IV)
• Clindamycin
• If MRSA:
  
  • Vancomycin
  • daptomycin
  • clindamycin
  • trimethaprim-sulfamethoxazole
  • linezolid

Question 3

Coagulase Negative Staph

Answer 3

Epidemiology

• live on skin and on mucous membranes
• preferentially colonize the skin (S. epidermidis, S. lugdunensis), sweat glands (S. haemolyticus), and uroepithelium (S. saprophyticus)
• infection more likely if pt has FB or intravascular device in place

Infections:

• all have to do w/ formation of biofilm because of “slime” produced resulting in smoldering infection
• prosthetic valve endocarditis
• catheter-associated bacteremia
• CNS shunt infection
• prosthetic device-associated infection
• peritoneal dialysis catheter-associated peritonitis
• UTI

S:

• purulent or serosanguineous drainage, erythema, pain, or tenderness at site of FB or device suggests infection
• instability and pain are signs of prosthetic joint infection
• fever, a new murmur, instability of new prosthesis, or signs of systemic embolization = prosthetic valve endocarditis
• immunosuppression and recent antimicrobial therapy are risk factors
• if possible, intravascular device or FB suspected should be removed
• sometimes if too risky, can treat with abx alone (probability of cure is reduced and sx management may be necessary)
• commonly resistant to beta-lactams and multiple other abx
• IV vancomycin is abx of choice until susceptibility to PCN-resistant PCNs or other agents has been confirmed

Question 4

Worrisome Antimicrobial Resistance

Answer 4

• Oxacillin resistance (MRSA)
• Vancomycin resistance (VRSA)
  
  • only a handful at this time but becoming a problem since Vanc is the drug we reserve for severe staph infections
• Inducible clindamycin resistance
• all three are difficult to detect in lac (have to take unusual measures to detect these)

Question 5

Staph aureus Toxic Shock Syndrome

Answer 5

S aureus produces toxins that cause 3 important entities:

1. “scalded skin syndrome” in kids
2. TSS in adults
3. enterotoxin food poisoning

originally ass w/ tampon use, any focus (nasopharynx, bone, rectum, vagina, abscess or wound) harboring a toxin-produing Staph aureus can cause TSS and nonmenstrual cases are common

S:

• abrupt onset of high fever, V, and watery D
• sore throat, myalgias, and HA are common

O:

• hypotension with kidney and heart failure is ass w/ poor outcome
• diffuse macular erythematous rash and nonpurulent conjuncitivis are common
• desquamation, especially of palms and soles, is typical during recovery

A:

• blood cx are negative b/c sxs are due to effects of toxin and not systemic infection

P:

• fatality rates may be as high as 15%
• rapid rehydration
• antistaph drugs
• management of kidney or heart failure
• addressing sources of toxin ie removal of tampon or drainage of abscess