Flashcards in Staphylococci Deck (30):
General characteristics of Staph
Hemolytic patterns not useful
Grows on mannitol salt agar, fermenting it and turning it yellow
Usually causes acute infection, but chronic in bones
Most infections are autochthonous
Reservoir for Staph aureus
Nose / skin. 1/3 of population are carriers.
Transmission of Staph aureus
Direct contact (mainly), endogenous, airborne, food poisoning
Does Staph aureus or Coag-Neg Staph cause more severe infections?
Best virulence marker for Staph aureus
Converts fibrinogen --> fibrin, which protects against phagocytosis
Function of the following Staph aureus antigens:
Cell wall - antiphagocytic
Teichoic acid - adherence via binding to fibronectin
Protein A - inhibits Ab-mediated clearance by phagocytes. Binds Fc portion of IgG.
Exotoxins (mechanism) - mediated by plasmid-lysogenic phages
Leukocidins - Kill white cells. Ex: Panton-Valentin Toxin
Soft-tissue toxin of community acquired MRSA. Forms pore --> lysis of RBCs and PMNs. Allows Staph aureus to penetrate into tissues.
Prototypical lesion of S aureus
If you see pus in a skin lesion, it's most likely Staph aureus
Most common infections w/ Staph
Furuncle / Boil
Caused by Staph aureus
Large abscess in skin / subQ. Drain pus and pack w/ gauze. High risk of bacteremia / metastatic infection
Caused by S aureus (bacteremia)
When furuncles coalesce and dive deeper into skin. Usually on back of neck.
Caused by Staph aureus and GAS
Superficial skin infection. Pus. Mainly affects face / limbs of young children
Caused by S aureus
Deeper infection of dermis and subcutaneous fat.
Tx w/ systemic AB’s
Caused by S aureus
Resolves on own
Staph Scalded Skin Syndrome
Caused by S aureus.
Most common in kids.
Caused by exfoliative toxin → splits intercellular connections in stratum granulosum → desquamation. Low mortality.
Staph aureus bacteremia
May be caused by IV catheter.
May lead to sepsis.
Mortality of nosocomial Staph infection is 25%.
25% chance of endocarditis as well
Staph aureus pneumonia
Common in pxs w/ bacteremia, endocarditis, or on ventilator. Risk in very young, elderly, post-viral infection, CF, COPD
Population and location
Staph aureus is #1 cause of osteomyelitis in children, mainly affecting long bones. Commonly affects spine / axial bones in adults. Bones may contain pus.
#1 cause of ventilator associated pneumonia (VAP)
Exotoxin food poisoning
“Enterotoxins" cause inflammation of GI tract, vomiting, diarrhea, usually in first 2-4 hrs after consumption. Sxs last 24 hrs. Fever is rare.
Self-limiting, rarely lethal.
Most commonly grows in ham, potato-salad, and custard-filled pastries when left at room temp.
Staph Toxic Shock Syndrome
Comparison to Strep TSS
TSST-1 is super-antigen
Diffuse erythema, desquamation of skin, hypotension, fever.
Not nearly as virulent as Strep TSS.
•Most often due to hyperabsorbant tampon use. 5% of women carry Staph aureus in vagina.
Low mortality. Infection ends when tampon is removed.
•Rare shock via post-surgical infection has high mortality.
General characteristics of Coag-Neg Staph
#1 cause of what?
Comparison to S aureus
#1 nosocomial pathogen in developed world.
Less virulent than Staph aureus. Does NOT cause shock.
Causes indolent, chronic infections
May take months / years to present.
Normal microbiota on skin and mucus membranes
Grows on mannitol salt agar but does not ferment.
Mainly transmitted via own flora during medical implantation. Can be direct contact.
Causes 90% of Coag-Neg Staph infections.
Colonizes skin and urethra
Causes UTI's in newly sexually active females
Diseases of Coag-Neg Staph
Medical devices - biofilms form on IV catheters, prosthetic heart valves, artificial joints, LVAD, breast implants, cranial shunts, and artificial lens.
Virulence factors of Coag-Neg Staph
Adhesins bind fibronectin for adherence.
Biofilms prevent phagocytosis.
AB resistance and tx for Coag-Neg Staph
Often resistant to beta-lactams and methicillin. Use vancomycin.
Susceptible hosts to Staph
Babies, neutropenia, IV catheters, IV drug users, diabetics, burn pxs, post-op, implanted medical devices
3 most common causes of cryptogenic bacteremia of healthy adults