Boy with acute pharyngitis Flashcards
In immunocompetent host, acute pharyngitis is caused by what?
Viruses or bacteria; NOT mycobacteria, fungi, parasites
Which bacteria other than strep A can cause pharyngitis? Why were they ruled out in this case?
Arcanobacterium haemolyticum; mycoplasma pneumoniae; group G/C strep —- all more common in teens/young adults
Corneybacterium diptheriae – only common in Africa/Asia
Neisseria gonorrhoeae – suggests child abuse
How are streptococcal bacteria grouped?
1930s - Rebecca Lancefield grouped by carbohydrate antigens on cell walls
How can strep groups be subdivided?
Based on serotype of surface-expressed M and T antigens
How is a strep A diagnosis made?
1) Rapid strep test.
- very specific, but sensitivity varies => negative does not rule out strep.
If strep negative:
2) Blood agar culture, 18-24h
Potential staph/strep colonies identified by beta-hemolysis patterns - sensitivity ~95%
3) Staph and strep differentiated with catalase test (strep negative)
From there, to identify strep group:
4a) (18-24h) Bacitiricin ring test
Clear zones indicates strep A
or 4b) PYR test (rapid) – look for red zone
What are petechiae?
Small red spots on roof of mouth
What virulence factors does strep have?
M protein – hair-like projections; allow adherence; impede pathogenesis; immunogenic
Streptolysin O – hemolyses RBS; destroyed by oxygen; immunogenic
Streptolysin S – hemolyses RBC, oxygen stable, nonimmunogenic
Streptokinase/DNAses/Hyaluronidase
Hyarulonic acid capsule
Strep pyrogenic exotoxins
What is rheumatic fever?
Occurs in 3% strep A patients
Joint pain, hear murmur due to valve damage.
Neurological chorea – abnormal involuntary movement affecting both sides of body
Immunologic response to strep M proteins can cross-react with human tissues => cardiovascular damage, potential for endocarditis later in life
What is acute glomeronephritis?
Occurs after skin infection with GAS
- Kidney disfunction with edema
- hypertension
- decreased urine output; blood/protein in urine
- kidney inflammation and presence of Ag/Ab/C complexes
What can be used to test previous strep A infection?
Presence of antistreptolysin O antibody or strep DNase B (for skin infection)
Can amoxicillin/penicillin be used to treat strep?
Yes - GAS do not produce beta-lactamase
What can be used instead of amoxicillin for those allergic to penicillins?
Erythromycin
What is the mechanism of action of bacitracin?
Blocks transport of peptidoglycan subunits across cytoplasmic membrane
Broad spectrum agains gram positive and negative bacteria
What is the method of action of penicillin / amoxycillin
Beta-lactams block crosslinking of peptide chains in peptidoglycan synthesis
Beta-lactams compete for binding sites of transpeptidases b/c similar shape to peptidoglycan subunit
Why is bacitracin rarely used in patients?
Nephrotixic
Usually combined with neomycin / polymixin in topical ointments e.g. neosporin
