Macrolide Resistance in Streptococcus pyogenes from Tonsillitis Patients: Phenotypic Profiles, Resistance Genes, and Clinical Associations

Background: Streptococcal tonsillitis is a global health challenge. The current study aimed to determine the frequency of macrolide resistance phenotypes and genotypes in S. pyogenes and to examine the association between resistance genes and clinical factors. Method: From 2019 to 2021, 159 S. pyogenes strains were isolated from children with tonsillitis. The macrolide resistance phenotype was determined by performing a double-disk diffusion test according to the Clinical and Laboratory Standards Institute guidelines. PCR has detected macrolide resistance genes. Results : In this study, 31.4% (50/159) of S. pyogenes strains were macrolide-resistant. The resistance rate was higher in isolates from females (33.7%, 32/95) than in isolates from males (28.1%, 18/64), but this difference was not significant (P = 0.459). Our results revealed that macrolide-resistant S. pyogenes is associated with tonsil hyperemia and hyperplasia ( P =0.044). Based on the double-disk diffusion test, the frequencies of M phenotype, cMLSB, and iMLSB among isolates were 27% (43/159), 3% (5/159), and 1% (2/159), respectively. The amplification of genes showed that 11.9% (19/159) of the strains harbored ErmC and 4.4% (7/159) carried ErmB genes. In contrast, both ErmA and Mef A genes were not detected in S. pyogenes isolates. On regression analysis, macrolide resistance was associated with tonsil hyperemia and hyperplasia (AOR: 3.780, 95%CI:1.244-11.487, P =0.019).There was no significant variation in the rate of resistance phenotypes or in the ErmA and MefA genes among subjects’ characteristics or clinical data. Conclusion: This study provides insight into the epidemiology of macrolide resistance in S. pyogenes within the study area. Although the rate of resistance is considerable, the findings should be interpreted with caution due to the limited sample size and absence of DNA sequencing data. Broader, multicenter studies incorporating molecular sequencing and whole-genome analysis are recommended to clarify the genetic basis of macrolide resistance in S. pyogenes.