Cutaneous Bacterial Infections Flashcards
Impetigo
Very contagious cutaneous infection by strep pyogenes or staph aureus
- staph aureus = generates bullae as well
Clostridium perfringens toxins
Perfingolysin O = pore forming
Alpha toxin (lecithinase or phospholipase C) - destroys cellular membrane and cannot be bound to antitoxins
Both toxins also cause clumping of leukocytes in blood vessels and prevent immune system from getting to the site they need to get to
Staphylococcus epidermis
Gram (+) cluster cocci
- contaminates blood cultures
- also creates biofilms so really bad with implants and catheters if not cleaned
Catalase (+)
Urease (+)
Coagulase (-)**
mannitol fermentation (-)**
** = differentiates it from staph aureus
Staph aureus
gram (+) grape cluster apperance
urease (+) Catalase (+)** Ferments mannitol* Coagulase (+)* - help fibrinogen bind to fibrin and produce clots
B-hemolysis (complete) on blood agar
- = differentiates between staph epidermis
- = differentiates between strep species
Possess unique protein A virulence factor
- binds host antibodies to prevent antibody actions
Also has a crap ton of usually virulence factors in high numbers
(Makes it a good pathogen if it gets into the body)
Staphylococcus aureus toxins
Cytotoxins
Exfoliative toxins = scalded skin syndrome due to mediated destruction of keratinocyte attachments at the stratum granulosum level
Enterotoxins = food poisoning
Toxic shock syndrome toxin = TSST
- causes fever, maculopapular rash and seaquamotion of palms and soles
- eventually if untreated = shock and death
Streptococcus pyogenes
Group A strep species that adheres to normal mucosa
- common infection in otitis media and acute pharyngitis
- B-hemolytic
- Gram (+) cocci
- catalase (-)**
- bacitracin sensative*
- = differentiates form GBS
- = differentiates from staph species
GAS virulence factors
Hyaluronic acid capsule
- resists phagocytosis and binds to CD44 on epithelial cells disrupting intercellular junctions and invasion of epithelium
M protein (major virulence factor)
- inhibits complement and phagocytosis
- **generates antibodies against it which leads to rheumatic fever
- **if not present = no virulence
Pyrogenic exotoxins
Severe disease from untreated GAS
Scarlet fever
- stupid high fever (>38.3C), sandpaper rash, strawberry tongue and circumferal palor
- lymphadenopathy cervical
Rheumatic fever
- M protein antibodies bind to cardiac sarcolemma
Rheumatic heart disease
Toxic shock-like syndrome
- caused by erythrogenic exotoxins A which triggers massive inflammatory response
Pseudomonas aeruginosa
Aerobic gram (-) rod
Lactase (-)
Oxidase (+)
Catalase (+)
Common for nosocomial UTIs
Also can cause
- sepsis
- ecthyma gangrenosum
- pneumonia
- osteomyelitis
- skin infections
Has a fruity/corn tortilla smell and blue pus due to pigments
Pathogenesis
- quorum sensing
- biofilms and slime layers
- toxins = endotoxins, phospholipase C and exotoxins A
Stress and pseudomonas
Stress leads to opioid formation which triggers quorum sensing in these bacteria
Quorum sensing activates virulence factors and worsening of the disease
Meningococcal meningitis shows what type of rash/skin lesion
Petechiae and pink macules with widespread eruption
- ** the rash DOENST blanch with pressure
Can induce gram (-) shock
Erysipelas
Superifcal facial cellulitis caused by strep pyogenes
Always show’s clear demarcation for he unaffected skin
Folliculitis
Caused primarily by staph aureus unless it shot tub folliculitis = pseudomonas areginosa
Clostridium perfringens
Gram (+) anaerobic rod
- spore former
Causes Gaseous gangrene in infected wounds since it gets deep in the tissue due to being anaerobic
Pathogenesis
- multiple subcutaneously
- causes anaerobic cellulitis which loses desmosomes and adherence junctions
- invasion of muscle tissues to get to anaerobic regions
- gas production = gas gangrene and compartment syndrome
