Laboratory diagnosis of Streptococcus pyogenes

Last Updated on February 4, 2021 by Sagar Aryal

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

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,