Bac of Skin, soft tissue, bone, and joint 2 Flashcards
Streptococcus - organism details:
- Gram positive cocci typically arranged in chains or pairs
- Aerobic and facultative anaerobic (i.e. can switch to anaerobic respiration)
- Culture typically on blood agar to determine hemolysis
- Catalase negative (unlike Staph.)
α-hemolysis:
yields a dark and greenish appearance due to chemical change in the hemoglobin in the red cells
β-hemolysis:
complete hemolysis of blood around and under colony
γ-hemolysis:
no color change or lysis
Lancefield antigens
Distinct carbohydrate structures derived from cell wall extracts used to define species of Strep (primarily β- hemolytic) into groups A through U
group A strep=
pyogenes
group B strep=
agalactiae
organism SENSITIVE to Bacitracin?
Strep pyogenes - Group A strep
transient colonization of Group A strep where?
URT and skin surface
Group A strep Virulence factor - capsule:
hyaluronic acid capsule is a poor immunogen and interferes with phagocytosis (looks like our own stuff)
Group A strep Virulence factor -Adhesins
- Pili/fimbrae
- LTA: involved in adhering to fibronectin on epithelial cell surface
- Protein F and M protein are involved in invasion of epithelial cell
Group A strep Virulence factor - m-protein
- myosin-like
- Binds many host molecules to facilitate cell invasion (fibrinogen, Ig, factor H) –> Inhibits complement activation
- variable N-terminus which defines the serotype
- Associated with virulent strains/invasion of epithelium
Group A strep Virulence factor -Toxins
- Streptolysin O and Streptolysin S == Pore forming toxins
- Strep Super Antigens (SAgs) - Increase proinflammatory cytokine production= pyogenic results
pyoderma (impetigo) distinguishing feature?
-often seen aroudn the mouth = honeycrusts
erysipelas - distinguishing feature?
-lesion is distinct from surroudning skin (USUALLY CAUSED BY STREP PYOGENES)
cellulitis (inflammation) - distinguishing feature?
-lesion IS NOT distinct from surrounding skin
most common superficial skin infection in children? organism?
- Impetigo - vesicles turn into pustules into honeycrust appearance
- usually Strep pyogenes
bullous impetigo is due to? how is this distinguished from other similar disease presentations from other organisms?
- Staph aureus
- distinguished from typical streptococcal infection by more extensive, bullous lesions that break down and leave thin paper-like crusts instead of the thick amber crusts of streptococcal impetigo (blisters = exfoliative toxin)
Necrotizing fasciitis - most common organism? key symptoms?
- group A strep = pyogenes
- starts out as not painful and looks slightly red but pain and tenderness become severe!
pain and tenderness is usually not very severe in which condition? In which condition is pain and tenderness very severe?
NOT-cellulitis
YES-necrotizing fasciitis
Necrotizing fasciitis - treatment?
- remove the dead tissue and then skin graft
- antibiotis to help - broad spectrum
Glomerulonephritis - causative organism where? how does it happen?
- group A strep BOTH PHARYNGEAL AND CUTANEOUS –> the kidney issues start after the pharyngeal/cutaneous
- type 3 hypersensitivity = immune complexes get stuck in kidney and that damaging stuff
Acute poststreptococcal glomerulonephritis (APSGN) - symptoms:
- hematuria, edema, hypertension, ± oliguria
- Reduced serum complement (CH50 and C3 –> get used up in the kidney issues)
- No evidence of systemic disease
- Recent streptococcal infection (serology or culture)
Streptococcal Toxic Shock Syndrome - caused by and some extra info she bolded…
- pyrogenic exotoxins = SpeA and SpeC
- most patients with streptococcal disease are bacteremic and many have necrotizing fasciitis.
- Shock and organ failure (e.g., kidney, lungs, liver, heart)