Objective To characterize the molecular profiles and antibiotic resistance patterns of Streptococcus A isolates collected from a grade III (A) hospital in Tianjin during 2022–2025 and their associations with clinical diseases..

Methods The resistances to 15 antibiotics of the Streptococcus A isoaltes were detected by micro-broth dilution method. Polymerase chain reaction (PCR) was conducted for the typing of emm gene, detections of erythromycin and tetracycline resistance genes (ermB, ermA, mefA, tetM, and tetO) and identifications of 11 superantigen genes (speA, speC, speG, speH, speI, speJ, speK, speL, speM, ssa, and smeZ).

Results In the 223 Streptococcus A isolates, 11 emm subtypes were identified, in which emm12.0 (67.26%) and emm1.0 (16.14%) were predominant. There was no differences in the proportions of the isolates with different emm subtypes in the patients with scarlet fever, impetigo and psoriasis (P >0.05). The resistance rates of the Streptococcus A isolates to tetracycline, erythromycin, and clindamycin were 96.86%, 98.65% and 97.76%, respectively, while all the Streptococcus A isolates were sensitive to all other tested antibiotics. THe differences in clindamycin resistance among the Streptococcus A isolates from scarlet fever, impetigo, and psoriasis patients were significant (P <0.05) , the clindamycin resistance rates of the Streptococcus A isolates from scarlet fever and impetigo patients were 97.26% and 95.45%, respectively, higher than 87.10% in psoriasis isolates. The predominant resistance genes were ermB (98.21%) and tetM (96.41%). The predominant superantigen genes were speG (96.41%), smeZ (97.76%), and speC (90.13%). The differences in the detections of speA, speH, speI, and speJ genes were significant between emm1.0 and emm12.0 isolates of Streptococcus A (P < 0.05). The scarlet fever isolates had higher proportions of speG (97.95%) and smeZ (97.95%), the psoriasis isolates showed higher proportions of speG (96.77%), speC (96.77%), and smeZ (100.00%), while the impetigo isolates exhibited higher proportions of speC (93.18%), speG (95.45%), and smeZ (100.00%). The differences in the carriage rate of ssa gene among scarlet fever, impetigo and psoriasis patients were significant (P < 0.05).

Conclusion During 2022-2025, the predominant Streptococcus A strains isolated in this hospital in Tianjin belonged to emm12 and emm1. The Streptococcus A isoaltes exhibited high resistance to macrolides, tetracyclines, and clindamycin, with tetM and ermB being the main resistance genes, while remained sensitive to all the other tested antibiotics. The distribution of ssa gene and clindamycin resistance exhibited significant associations with clinical diseases, which can be used important molecular epidemiological evidence for the clinical precision treatment and control of Streptococcus A infection.