[emm Typing of Streptococcus pyogenes Isolates: A Real-Time PCR-Based Approach]

In recent years, Streptococcus pyogenes infections have maintained their clinical and epidemiological significance in parallel with the reported increase in invasive group A streptococcal (iGAS) disease and scarlet fever cases. This study aimed to evaluate the coverage of emm typing using a real-time polymerase chain reaction (Rt-PCR) based method which can be used as an alternative to sequencing due to its rapid and cost-effective approach in a potential S.pyogenes outbreak. In addition, determination of emm type distribution was performed to provide updated local epidemiological data and to assess vaccine coverage of the study period. Between February 2024 and May 2024, 106 S.pyogenes isolates obtained from various clinical samples were subjected to emm typing using a quadriplex Rt-PCR kit designed according to the Centers for Disease Control and Prevention protocol and the presence of 20 commonly observed emm types was investigated. To validate the emm types identified by Rt-PCR, one isolate from each emm type and 31 isolates that could not be typed by Rt-PCR were subjected to sequence analysis. Antimicrobial susceptibility testing was performed using the disk diffusion method. While 81.1% of the patients belonged to the pediatric age group, 64.8% of iGAS infections were detected in adult patients. emm types were successfully identified by Rt-PCR in 70.8% of the S.pyogenes isolates. Sequencing results obtained for representative isolates were concordant with the corresponding Rt-PCR findings. With the inclusion of sequencing data, a total of 12 different emm types were identified, with emm3 being the predominant type, followed by emm2, emm6 and emm89. Among isolates with determined emm types, the coverage of the 30-valent vaccine was calculated as 100%. All isolates were susceptible to penicillin, whereas resistance rates of 12.3% to tetracycline, 2.8% to erythromycin and 1.9% to clindamycin were observed. In conclusion, Rt-PCR-based emm typing represents a reliable, rapid and feasible alternative for S.pyogenes in centers lacking sequencing facilities. It is anticipated that optimizing primer and probe designs to adequately cover S.pyogenes isolates circulating in the country may further improve the typing performance of Rt-PCR assays. Moreover, the development of a laboratory-based active surveillance system is essential to ensure the continuity of local epidemiological data.