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Volume 47, Number 4, August 2014

Molecular characterization of Group A streptococcal isolates causing scarlet fever and pharyngitis among young children: A retrospective study from a northern Taiwan medical center 


Po-Chuang Wu, Wen-Tsung Lo, Shyi-Jou Chen, Chih-Chien Wang


Received: July 18, 2012    Revised: January 3, 2013    Accepted: January 18, 2013   

 

Corresponding author:

Chih-Chien Wang, Corresponding author. Department of Pediatrics, Tri-Service General Hospital, National Defense Medical Center, Number 325, Cheng-Kung Road, Section 2, Neihu, Taipei 114, Taiwan, ROC. 



 

Background and purpose: 

Little information is available on the differences in frequency of pyrogenic exotoxin genes between strains of group A streptococci that cause scarlet fever and those that cause pharyngotonsillitis in children in Taiwan. This study retrospectively monitored the presence of pyrogenic exotoxin genes, the emm typing, and the susceptibility of macrolide drugs in Streptococcus pyogenes isolated from children diagnosed with scarlet fever and pharyngotonsillitis in northern Taiwan. 



 

Methods:

Isolates of S. pyogenes were recovered from children with scarlet fever (n = 21) and acute pharyngotonsillitis (n = 29) during 2000–2011. The isolates were characterized according to the presence of spe genes and emm typing. Antibiograms were determined by the disk diffusion method and agar dilution test. Polymerase chain reaction was used to detect the presence of erm genes in isolates that showed nonsusceptibility to erythromycin. All isolates underwent additional genotyping by pulsed-field gel electrophoresis. 



 

Results:

In isolates from patients with scarlet fever, the frequencies of pyrogenic exotoxin genes were 9.5% for speA, 81.0% for speB, 4.8% for speC, and 71.4% for speF. In isolates from patients with pharyngotonsillitis, the frequencies were 17.2% for speA, 72.4% for speB, 13.8% for speC, and 69.0% for speF. There were no significant differences in frequencies of the exotoxin genes between the two groups of isolates. Eight emm sequence types were identified from all group A streptococci isolates. The most common types were emm12 followed by emm1 and emm4. The erythromycin resistant rate was 4/50 (8%). The ermB gene was detected in only one isolate from a patient with pharyngotonsillitis. Pulsed-field gel electrophoresis had a total of three sets of clustered strains, which showed >80% homology and belonged to the same emm type.
 



 

Conclusion:

There were no significant differences in frequencies of the spe genes between S. pyogenes isolates from patients with scarlet fever and patients with pharyngotonsillitis. The most common emm type was emm12. Low erythromycin resistance in S. pyogenes was observed. 



 

Key words:

Scarlet fever, Streptococcal pyrogenic exotoxin, Streptococcus pyogenes