Case-Based Study Questions - Streptococcus pyogenes

Clinical Features

-recent onset red eye
-tearing, irritation, foreign body sensation

Epidemiology

-acute purulent conjunctivitis with chemosis and pseudomembrane
-source may be exogenous or endogenous
-person-to-person spread by respiratory droplets (pharyngitis)
-children 5-15 y/o are most susceptible
-transmitted through breaks in skin after direct contact with infected person, fomite, or arthropod vector

Microbiology

-sensitive to bacitracin (A disk)
-hyaluronic acid-containing capsule: spreading factor that helps bacteria extend through subcutaneous tissue
-β-hemolytic
-conjunctival membrane and pseudomembrane associated with bacterial conjunctivitis may be produced in associated with:
→Neisseria gonorrhoeae
→β-hemolytic streptococci
→C. diphtheriae

Virulence Factors

-capsule: nonimmunogenic and antiphagocytic
-M protein: immunogenic, inhibits opsonization
-F protein (lipoteichoic acid): mediate adherence to mucoepithelium by binding to fibronectin
-C5a peptidase: reduces inflammatory responses mediated by C5a

Diagnostic Tests

-gram stain: purple in pairs or chains
-sheep blood agar: β-hemolysis

Treatment

-antibacterial agents for ocular infection (Pseudomembranous Conjunctivitis) → Fluoroquinolones: Levofloxacin (Quixin) and Moxifloxacin (Moxeza)
-streptococci is sensitive to penicillin
-oral macrolide for penicillin-allergic patients
-IV penicillin + clindamycin for systemic infections