Staphylococci Flashcards
General characteristics of Staph Morphology Hemolysis O2 preference Agar Presentation Source
Clusters
Hemolytic patterns not useful
Facultative
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?
Staph aureus
Best virulence marker for Staph aureus
Function
Coagulsase
Converts fibrinogen –> fibrin, which protects against phagocytosis
Function of the following Staph aureus antigens: Cell wall Teichoic acid Protein A Exotoxins (mechanism) Leukocidins
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
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
Abscess
If you see pus in a skin lesion, it’s most likely Staph aureus
Most common infections w/ Staph
Skin infections
Furuncle / Boil Caused by Characteristics Tx Risks
Caused by Staph aureus
Large abscess in skin / subQ. Drain pus and pack w/ gauze. High risk of bacteremia / metastatic infection
Carbuncle
Caused by
Characteristics
Location
Caused by S aureus (bacteremia)
When furuncles coalesce and dive deeper into skin. Usually on back of neck.
Impetigo 2 causes Characteristics Location Population
Caused by Staph aureus and GAS
Superficial skin infection. Pus. Mainly affects face / limbs of young children
Cellulitis
Cause
Characterstics
Tx
Caused by S aureus
Deeper infection of dermis and subcutaneous fat.
Tx w/ systemic AB’s
Folliculitis
Cause
Tx
Caused by S aureus
Resolves on own
Staph Scalded Skin Syndrome Cause Population Mechanism Mortality?
Caused by S aureus.
Most common in kids.
Caused by exfoliative toxin → splits intercellular connections in stratum granulosum → desquamation. Low mortality.
Staph aureus bacteremia
Cause
Risks
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
Risk factors
Common in pxs w/ bacteremia, endocarditis, or on ventilator. Risk in very young, elderly, post-viral infection, CF, COPD
Osteomyelitis
Cause
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)
Staph aureus
Exotoxin food poisoning Sxs Timing Risks Common foods
“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 Antigen Sxs Comparison to Strep TSS Cause Risk Tx
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
Presentation
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.
Staph epidermidis Coagulase? Reservoir Hemolysis Agar Oxygenation Transmission
Coag-Neg
Normal microbiota on skin and mucus membranes
Non-hemolytic
Grows on mannitol salt agar but does not ferment.
Facultative
Mainly transmitted via own flora during medical implantation. Can be direct contact.
Causes 90% of Coag-Neg Staph infections.
Staph saprophyticus
Reservoir
Main disease
Colonizes skin and urethra
Causes UTI’s in newly sexually active females
Diseases of Coag-Neg Staph
SSI’s
Folliculitis
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
Staph aureus
Meningocccus
GAS
General treatment for Staph If resistant? If allergic? Soft tissue infections? Abscess? Bacteremia / endocarditis?
•Penicillin if susceptible (rare)
•Methicillin (nafcillin or oxacililn) or dicloxiacillin if penicillin resistant. Cephalosporins / carbapenems may also be used.
Clindamycin if allergic to penicillin.
•Vancomycin if methicillin-resistant.
•Linezolid or Daptomycin if vancomycine-resistant. Daptomycin does NOT work to tx pneumonia. Linezolid does NOT work for bacteremias.
•Soft tissue infections – use clindamycin, TMP-sulfa, or minocycline
•Abscesses – main tx is incision / drainage. AB may be used depending on site.
•Bacteremia and endocarditis require multiple-week IV AB therapy
