Streptococcus pyogenes is the leading cause of uncomplicated bacterial pharyngitis and tonsillitis commonly referred to as strep throat. Erythromycin is administered for patients allergy to penicillin. In this study, 125 throat swab samples were collected from children between 2-12 years old with tonsillo-pharyngitis attended to at the AL-Imammain AL-Kadhimain Medical City-Baghdad-Iraq and Pediatric Caring Hospital-Baghdad-Iraq from February 2014 to February 2015. Only 72 throat swab samples showed bacterial growth. The isolates were identified using Vitek 2 Compact system for Gram-Positive. Antibiotics susceptibility was examined using the BioMérieux Vitek2 compact system AST card. For direct molecular identification of S. pyogenes, 16S rRNA and 16S-23S rRNA gene amplification were used. Molecular screening for erythromycin resistance genes erm(A), erm(B) and mef(A) were done using PCR. The results of identification using Vitek2 GP show that 21 (29.2%) samples were S. pyogenes-positive while 51(70.8%) of samples were due to other causes of tonsillo-pharyngitis. The results of molecular identification of S. pyogenes strains using 16S rRNA and 16S-23S rRNA amplification showed that only four strains were positive for 16S-23S rRNA, while two strains out of four were also positive for 16S rRNA. According to the results of antibiotic sensitivity, there were seven strains resistant to erythromycin. The results of molecular screening for erythromycin resistant genes showed that all these resistant strains did not contain the resistant genes erm(A), erm(B) or mef (A). We conclude that, maybe there was a specific sequence variations in genes used for identification of S. pyogenes. Also, resistance to erythromycin could be attributed to causes other than the studied mutations, such as structural modification of erythromycin by phosphorylation, glycosylation or lactone ring cleavage by erythromycin esterase.
Key words: Streptococcus pyogenes, molecular identification, erythromycin resistance genes.
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