A Pilot Molecular Study on The Association Between Sortase Genes (SrtA, SrtB, SrtC) and Antibiotic Resistance in Clinical Isolates of Streptococcus Pyogenes
Author(s):
Noor Thamer Ghaffoori
Date: 20/10/2026
doi: https://doi.org/10.5281/zenodo.8425890
Abstract
Background: Streptococcus pyogenes is a major human pathogen causing respiratory tract
infections. The occurrence of macrolide resistance has created a clinical concern to the
effectiveness of treatment and control of the disease. The objectives of this study were to
molecularly confirm the identity of Streptococcus pyogenes isolates, to identify the presence
of sortase genes (srtA, srtB, and srtC) and to assess the statistical correlation between these
genes and the phenotypic resistance to the antibiotics. The methods used to collect the
specimens were throat and tonsil swabs from patients with symptoms of respiratory tract
infections, done on a total of 300 patients. Standard microbiological testing was followed by
PCR confirmation with the diagnostic spy1258 gene, to identify and isolate bacteria. Antibiotic
susceptibility test was done by the Kirby-Bauer disk diffusion method as per CLSI guidelines.
The srtA, srtB and srtC genes were detected using PCR assays. Results: Out of 300 samples,
16 (5.33%) were found to be positive for S. pyogenes. The srtA gene was found in all 16
isolates (100%), the srtB gene was present in 43.75% of isolates and srtC gene was present in
81.25% of isolates. All three sortase genes were present in 7 (43.75%) of the isolates. All the
isolates were sensitive to penicillin G (100%), whereas resistance was noted to erythromycin
(62.5%), tetracycline (50%) and clindamycin (37.5%). Fisher's Exact Test showed that there
was a significant relationship between the presence of the triple gene combination
(srtA+srtB+srtC) and resistance to both erythromycin (p = 0.011) and clindamycin (p = 0.001).
Conclusions: The distribution of multiple sortases, especially srtC, seems to be linked to higher
macrolide resistance of S. pyogenes. This correlation indicates an indirect involvement of
sortase enzymes in antibiotic tolerance, probably as an aid for pilus assembly and biofilm
formation.
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