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Streptococcus pyogenes (Group A streptococci: GAS) are known to cause a wide variety of human illnesses, some of which can be life-threatening. Usually, penicillin is the first-choice agent for the treatment of GAS infections. For patients with penicillin or beta-lactam antibiotics allergies, macrolide drugs are recommended as an alternative therapy. However, an increased prevalence of macrolide-resistant GAS (MRGAS) has been reported in many countries. Furthermore, fluoroquinolone non-susceptible GAS has been reported. The present study was focused on determining the features of fluoroquinolone non-susceptible strains collected from children with pharyngotonsillitis in the southwestern areas of Japan. To reveal the characteristics of fluoroquinolone non-susceptible GAS, we investigated the MIC, T-serotype, emm typing, and PFGE of 298 GAS strains isolated in the Fukuoka southwest area of Japan between 2011 and 2013. We determined that fluoroquinolone non-susceptibility shows a MIC to tosufloxacin of ≧1 μg/ml. We identified 33 (11.1%) fluoroquinolone non-susceptible GAS strains. In these strains, 6 T-serotypes and 9 emm /MLST patterns were detected. The predominant combinations were emm 6/ST382 (14 strains, 42.4%) and emm 89/ST101 (5 strains, 15.2%). PFGE classified 10 pulsotypes, and each was quite different. These results showed that fluoroquinolone non-susceptible GAS strains have a variety of origins. The usage of fluoroquinolone drugs could have a negative effect on the antimicrobial drug sensitivity of GAS in Japan. Considering such a situation, continuous monitoring of quinolone non-susceptible GAS is necessary. [ABSTRACT FROM AUTHOR]

Introduction. Pharyngotonsillitis caused by Streptococcus pyogenes (group A streptococci, or GAS) is among the most common infections treated with antibiotics in pediatric patients. Aim. This study aimed to analyse changes in molecular epidemiology and antibiotic susceptibility among GAS isolates in three study periods spanning 10 years. Methodology . GAS isolated from paediatric patients with pharyngotonsillitis during Period I (mid-2007 to 2008, n =235), Period II (2012, n =210), and Period III (2018, n =189) were analysed for emm type, multilocus sequence type (MLST), antibiotic susceptibility, and macrolide (ML)- and quinolone (QL)-resistance genes. Results. Over 20 % of isolates represented emm 1 and emm 12 types, remaining common in all three periods. Among other emm types, emm 4 was common in Period I, emm 28 and emm 89 in Period II, and emm 3 and emm 89 in Period III. All isolates remained highly susceptible to penicillins and cephalosporins. Isolates possessing mefA, ermA, or ermB genes mediating ML resistance increased from 34.9 % in Period I to 60.9 % in Period II, but fell to 27.5 % in Period III. QL-resistant isolates with amino acid substitutions affecting ParC and/or GyrA gradually increased from 11.5 to 14.3 %. Specific sequence types identified by MLST and emm typing were associated closely with ML or QL resistance. Conclusion. Our findings indicate that even in ambulatory care, antibiotic choice for these infections should be based on rapid identification and characterization of causative pathogens.