Bacterial Infections of the Skin Flashcards
What is an Erysipelas? What pathogen is it caused by?
Acute Streptococcus pyogenes (GAS) infection of the upper dermis and superficial lymphatics
What is Cellulitis? What pathogen is it caused by?
Severe inflammation of dermal and subcutaneous layers of the skin commonly caused by Streptococcus pyogenes (GAS)
What is Necrotizing Fasciitis? What pathogen is it caused by?
Rare infection of deep layers of the skin and subcutaneous tissues usually due to Streptococcus pyogenes (GAS) that produces superantigen.
Tx for GAS infection of skin
Penicillin G and erythromycin
What is post streptococcal nephritis?
Condition analogous to Rheumatic fever but tends to follow skin infection rather than pharyngitis associated with the “M-protein” that is a virulence factor. Cross-reactivity of anti-M Abs causes inflammation in the kidney.
General and structural features of staphylococci
G(+) clusters, look like grapes, non-motile, no spores, make catalase (decomposes H2O2), Protein A (binds Ig), anti-phagocytic capsule
S. aureus culture characteristics
Gold colonies that are susceptible to bacteriophages, Beta hemolytic
S. aureus reservoir and transmission
Nose and skin, direct contact with infected person or indirectly by fomites
6 S. aureus toxins and their effects
Coagulase - coagulate plasma, Protein A - Binds Ig, Enterotoxin - GI irritation, Exfoliatin - Generalized desquamation, Leukocidin - Kills white cells, Toxic shock syndrome toxin - Shock
3 S. aureus skin infections
Abscesses (furunculitis - superficial sweat glands/hair follicle infections), Impetigo - mixture of Strep and Staph, Scalded skin syndrome/Toxic shock syndrome - Circulating toxin from Staph
Dx of S. aureus skin infection
Clinical appearance and history, Smears from pus, cultures showing G(+) cocci, coagulase positive, beta hemolytic
Tx for S. aureus skin infection
Remove dead tissue and bacteria, 1) Penicillin; if resistant to penicillin 2) Oxacillin/Methicillin; if resistant 3) Vancomycin if resistasnt, you’re screwed
Prevention of S. aureus skin infection
Wash hands, cover lesions, treat carriers (nose/skin) topically, remove carriers from ICU, operating rooms, and newborn nurseries, isolate children with recurrent lesions
Characterization of Staphylococcus epidermidis
Catalase positive, coagulase negative, nonhemolytic
In what scenarios are S. epidermidis infections commonly seen?
Infections of catheters, iv lines, shunts, other medical devices, piercings. STICKS TO PLASTIC AND NYLON
