Last Updated on January 1, 2020 by Sagar Aryal
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
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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