Flashcards in Exam #8: SSTI II Deck (43):
List the characteristics of S. pyogenes.
- Gram (+) cocci in chains
- Catalase negative
- Group B
- Lancefield A
What is the difference between a, b, & g hemolysis?
A= green, partial hemolysis
B= complete hemolysis
G= no hemolysis
What are the Lancefield antigens?
- Lancefield antigens are named after the woman that discovered them, Rebecca Lancefield
- These are group specific cell wall carbohydrate structures used to define species of Strep.
- Mostly refers to beta-hemolytic strep
What is the strep. associated with Lancefield A?
S. pyogenes (which is Beta-hemolytic)
What is the strep. associated with Lancefield B?
What is the strep. associated with Lancefield D?
What infections are caused by GAS?
Remember GAS= S. pyogenes:
Skin & soft tissue infection
How is GAS transmitted?
Respiratory droplets or breaks in the skin
What is the capsule associated with GAS?
HA capsule (looks like self; we don't make antibodies)
What are the adhesins associated with GAS?
What is M protein?
Myosin-like protein that facilitates adhesion, anti-phagoyctosis, and prevents complement activation
- variable regions are associated with differential virulence
What toxins are associated with GAS?
- Streptolysin O & S= pore forming toxins for invasion of host & destruction of tissue
What are the functions of Streptolysin O & S?
List three other virulence factors associated with GAS and their functions.
- Strep Super Antigens (SAgs), which are superantigens that increase proinflammatory cytokine production (Scarlet Fever, STS, & nec. fas)
- C5a peptidase= degrades chemotactic C5a
- DNAse= depolymerize DNA in pus decreasing viscosity
- Streptokinase= cleaves plasminogen
Describe the pathogenesis of GAS.
1) M-protein mediates adhesion
2) Streptolysin-O forms pores in the membrane
4) C5a blocks recruitment of neutrophils
List the skin & soft tissue infections that can be caused by GAS.
What is Impetigo?
- Honey crusted lesions most seen around the mouth
- Most commonly caused by S. aureus but also caused by S. pyogenes
*Note that if you culture and see Gram (+) cocci, you WILL NOT know the difference; also, bullous impetigo is not seen in s. pyogenes
What is Erysipelas?
- Bright red appearance of the involved skin which forms a plateau of sharply demarcated tissue from the surrounding normal skin
- Most commonly caused by S. pyogenes
- Can be associated with fever
What is the difference between Erysipelas and cellulitis? What is the most common cause of cellulitis?
- Cellulitis has a deeper involvement and is NOT well demarcated
- S. pyogenes
What is Necrotizing fasciitis?
A severe infection said to be caused by "flesh-eating bacteria"
- Most commonly caused by S. pyogenes
- Secondarily caused by S. aureus
*Pain and tenderness are SEVERE; pain out of proportion to exam initially
What is the presentation of Nec. Fas.?
- Initially grey skin
- Pain out of proportion to exam
How is Nec. Fas. treated?
What are the characteristics of Scarlet Fever?
- Complication of GAS
- Caused by TOXIN released by GAS
- Diffuse erythematous rash
- Strawberry tongue
What is Rheumatic Fever?
- Complication of S. pyogenes pharyngitis
- Characterized by inflammatory changes involving the heart, joints, blood vessels, and subcutaneous tissue
What is Glomerulonephritis?
Type III Hypersensitivity that usually follows cutaneous infection
- Antigen/ ab complexes activate complement in the kidney
- Seen 3-6 weeks following GAS skin infection
What are the symptoms of post-streptococcal glomerulonephritis?
How is post-streptococcal glomerulonephritis diagnosed?
There will be evidence of recent streptococcal infection via serology: (though skin infection will be gone)
- Anti-streptolysin O antigen
- Reduced serum complement
What is Streptococcal Toxic Shock Syndrome? How is this different from the TSS that is seen with S. aureus?
- Superantigen induced shock and organ failure
- Most patients with streptococcal TSS are bacteremic & have nec. fas.
How is streptococcal skin infection diganosed?
- Culture followed by Lancefield (A i.e. GAS)
- Direct Ag detection
Anti-streptolysin O (ASO) antibodies in serum (ASO)= previous exposure
How is S. pyogenes infection treated?
List the characteristics of P. aeruginosa.
Gram (-) rod
*Makes pyocyanin (blue-green pigment)
When is P. aeruginosa most commonly seen?
Opportunistic pathogen; patient already has infection
Is P. aeruginosa capsulated?
Yes, mucoid polysaccharide capsule
What toxin is associated with P. aeruginosa?
What is the mechanism of Exotoxin A?
- A/B Toxin that inactivates EF-2 via ADP ribosylation & blocks protein synthesis
- Similar to the Diptheria toxin
List the infections that are caused by P. aeruginosa
Skin and soft tissue infections in the immunocompromised:
- Burn victims
- Cystic fibrosis patients
Osteochondritis (penetrating injury) caused by a penetrating injury when the person is wearing a sock
How does bacteremia in the presence of P. aeruginosa present?
What is Ecthyma gangrenosum?
Purple macule that develops rapidly into a hemorrhagic bulla that ruptures
What is Pseudomonas folliculitis?
"Hot tub" folliculitis
*Pseudomonas can withstand very high temperatures and chlorine
What causes "green nails" associated with P. aeruginosa?
- This is essentially a paronychia that is caused by Pseudomonas infection
- Pyocyanin in P. aerugenosa causes the nails to turn green
- Seen in patients with wet hands
What is webspace intertrigo?
Eroded space between toes that is most commonly caused by P. aeruginosa
How is P. aeruginosa treated?
- Varies with presentation
- *Abx resistance is a huge problem*