Agents of Bacterial Skin Infection

1. Impetigo--confined to epidermis, looks bad but generally not serious
2. Erysipelas--involves dermal lyphatics, rare but serious
3. Cellulitis--subcutaneous fat layer, common and very serious, hospitalizable

1. Invasive
2. Tend to produce purulent (pus-filled) lesions
3. Obligate extracellular bacteria
4. Have anti-phagocytic virulence factors

1. Gram positive cocci (usually in chains or pairs)
2. Beta-hemolytic
3. Catalase negative
4. Bacitracin sensitive

1. M protein
1. anti-phagocytic
2. many different antigenic types, some that create molecular mimicry
2. Hyaluronc acid capsule
1. anti-phagocytic

1. Pharyngitis--rarely accompanied by Scarlet Fever
2. Impetigo
3. Erysipelas--rare
4. Cellulitis
5. Necrotizing fasciitis
6. Streptococcal toxic shock syndrome--most serious

infections due to wet skin

--especially troops during training or combat with wet or damp boots

cutaneous lesion that develops secondary to pressure injury and is informally referred to as a bed sore

--constant pressure of an immobilized pt can lead to skin necrosis and possible secondary infection

1. rheumatic fever
1. cross-reaction between anti-M antibodies and the heart tissue
2. pts with rheumatic fever are on Penicillin for long-term to keep subsequent infections at bay
2. acute glomerulonephritis
1. renal injury due to antigen-antibody complexes in glomeruli

β-hemolytic

    --clear zone of complete hemolysis on the blood agar plate

group of infections that affect the skin and soft tissues

---most common in preschool kids and in hot humid weather

fever-causing

---compared to pyogenic which is pus-forming

• structures on or released by bacteria that can nonspecifically activate a large subset of T cells
• the resulting massive release of proinflammatory cytokines by the activated T cells results in a sepsislike clinical picture with shock and multiorgan failure
• those cytokines are IFN-γ and TNF-α

Catalase

    Strep--catalase neg

    Staph--catalase pos

strawberry tongue

pallor of face

desquamation of skin

intraepidermal vesicles filled with exudates

common in children in warm, moist environments

subcutaneous tissue

erythema, induration, heat and pain

indistinct borders

superantigenic

bacteria possible

often occurs in 6-15 year olds after throat infection with certain rheumatogenic M types of group A streptococci

CROSS-REACTION between anti-M antibodies and heart tissue

• Pediatric Autoimmune Neuropsychiatric Disorder Associated with Gorup A Streptococci
• presence of OCD and/or tic disorder
• association with GAS infections

• after throat or skin infection with certain nephritogenic M types
• renal injury due to deposition of antigen-antibody complexes on glomeruli