Laboratory diagnosis of Streptococcus pyogenes

1. Specimens

  • Throat swab
  • Pus
  • Cerebrospinal fluid
  • Blood
  • Serum for antibody determinant

2. Smear

  • Gram staining
  • Purple color cocci in chain arrangement
  • Not to be confused with Viridans Streptococci from throat swab sample since both have same appreance

Laboratory diagnosis of Streptococcus pyogenes

3. Culture

  • Culture on blood agar
  • Addition of bacitracin in inoculum: S pyogenes are sensitive to bacitracin
  • Colonial appearance: Grayish white, transparent to translucent, matte or glossy; smooth; flat;large zone of beta hemolysis
  • Catalase negative, oxidase negative and PYR positive

4. Antigen detection tests

  • Enzyme immunoassay (EIA)
  • Agglutination test
  • Kits uses enzymatic or chemical method to extract antigen from throat swab and demonstrate the presence of antigen using EIA or agglutination test (visible clumping)
  • More sensitive assays are DNA probes and Nucleic acid amplification techniques

5. Serologic tests

  • Detection of antibody titer after 3 to 4 weeks after exposure to organism
  • Antibodies include ASO, anti-DNase B, anti- hyaluronidase, antistreptokinase, anti- M type specific antibodies
  • Anti Streptolysin O (ASO) is most widely used.

Treatment of Streptococcus pyogenes

  • S pyogenes are susceptible to penicillin (benzylpenicillin (penicillin G) or oral phenoxymethylpenicillin (penicillinV)
  • For penicillin allergic patients, erythromycin is a drug of choice
  • In some cases clindamycin or vancomycin is also recommended

Prevention and control of Streptococcus pyogenes

  • Maintenance of personal hygiene
  • Chemoprophylaxis: prophylactic use of antibiotics in some streptococcal infections: rheumatic fever,

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