Serotype distribution, antibiotic resistance patterns and molecular characteristics of serogroup 6 Streptococcus pneumoniae isolates collected from Chinese children before the introduction of PCV13.

OBJECTIVES: Streptococcus pneumoniae is an important pathogen in infectious diseases worldwide, and serogroup 6 S. pneumoniae strains are very common in China. This study investigated the serotype distribution, antibiotic resistance patterns and molecular characteristics of 215 serogroup 6 S. pneumoniae isolates collected from hospitalised children in China during 2013-2016.

METHODS: Serotypes were determined using the Quellung reaction with antisera. Antibiotic resistance against 11 antimicrobials was tested by Etest or the disk diffusion method. Sequence types (STs) were assigned using multilocus sequence typing (MLST). Data analysis was performed with WHONET 5.6 software.

RESULTS: The percentages of serotype 6A, 6B, 6C and 6D among the 215 serogroup 6 isolates were 50.7% (109/215), 36.3% (78/215), 12.6% (27/215) and 0.5% (1/215), respectively. All isolates were susceptible to levofloxacin and were resistant to erythromycin. No isolate was resistant to parenteral penicillin, but the intermediate and resistant rates reached 72.6% (156/215) and 5.1% (11/215), respectively, based on the oral breakpoint. Sixty-seven STs were detected, with 14 STs being newly assigned. The most common clonal complexes (CCs) were CC3173 (26.5%; 57/215), CC9789 (13.5%; 29/215), CC90 (13.0%; 28/215) and CC902 (8.8%; 19/215), and the non-susceptibility rates of these four CCs against penicillin and cefuroxime (penicillin, 98.2%, 100%, 100% and 100%, respectively; cefuroxime, 98.2%, 100%, 96.4% and 94.7%, respectively) were higher than the overall level of serogroup 6 isolates (penicillin, 77.7%; cefuroxime, 70.2%).

CONCLUSIONS: Serotype 6A is the most common serotype of serogroup 6 S. pneumoniae strains in Chinese children, and different CCs/STs express diverse antibiotic resistance patterns.