Prevalence and Molecular Characterization of Macrolide Resistance in Clinical Isolates of Beta Hemolytic Streptococci from a Tertiary Care Teaching Hospital in Kerala, India

 Beta-hemolytic streptococci (BHS) are responsible for both invasive and noninvasive infections, and the preferred treatment for these infections is penicillin due to the distinctive characteristics of these bacteria. However, in patients who cannot tolerate β-lactam antibiotics, macrolides and clindamycin are important alternative options for treating BHS infections. This study aimed to analyse the pattern of macrolide resistance among clinical strains of beta-hemolytic streptococci (BHS).

 Beta hemolytic streptococci isolated from clinical specimens during December 2018 to May 2020 were included in this study. Identification of the isolates were done by conventional and Vitek 2 method. All isolates were subjected to serogrouping. Antibiotic susceptibility testing done by disc diffusion method. Genes encoding macrolide resistance were detected by conventional multiplex polymerase chain reaction.

  A total of 129 beta hemolytic streptococcal isolates were obtained which included 27 S. pyogenes (20.9%), 77 S.agalactiae (59.7%), 23  S.dysgalactiae spp equisimilis (17.8%) and one isolate of S.anginosus and  S. porcinus each (0.8%). Erythromycin, clindamycin, quinuprisitn and tetracycline resistance were found to be 20.2%, 12.1%, 16.3% and 51.2% respectively. Among the 26 erythromycin resistant isolates, 12(46.2%) were inducible clindamycin resistant phenotype.  Out of 26 erythromycin resistant isolates, 7(26.9%) isolates were harbouring erm(A) gene, 10(38.5%) erm(B) and 9(34.6%) mef(A) gene.

 Our study highlights the importance of routine antibiotic susceptibility testing for beta-haemolytic streptococci, as well as the detection of inducible resistance to prevent therapeutic failure.