Whole-genome sequencing analysis of multidrug-resistant serotype 15A Streptococcus pneumoniae in Japan and the emergence of a highly resistant serotype 15A-ST9084 clone [Mechanisms of Resistance]

Since the introduction of pneumococcal conjugate vaccines, an increase in the incidence of disease attributable to serotype 15A-ST63 pneumococci has been observed in many regions worldwide. We conducted a nationwide pediatric pneumococcal infection surveillance study between 2012 and 2014 in Japan. In the surveillance study, we detected multidrug-resistant serotype 15A-CC63 strains (resistant to macrolides, penicillin, cefotaxime and meropenem); in this study, we analyzed these resistant isolates to determine the dynamics and mechanism of resistance using whole-genome sequencing. In most of the penicillin-, cefotaxime- and meropenem-resistant strains, recombination occurred in the pbp2x region resulting in the acquisition of additional cefotaxime resistance to penicillin and meropenem. In the multidrug-resistant serotype 15A-CC63 strains, we identified a specific clone with ST9084, and all of the isolates were recovered from Yamaguchi prefecture in Japan. All of the serotype 15A-ST9084 isolates had a novel pbp2x-43 that was inserted by recombination events. The conserved amino acid motif profiles of pbp1a, pbp2b and pbp2x of the strains were identical to those in serotype 19A-ST320. A Bayesian analysis-based date estimation suggested that this clone emerged in approximately 2002 before the introduction of PCV in Japan. This clone should be monitored because serotype 15A is not contained in the currently used PCV13 and it was resistance to beta-lactams, which are often use in a clinical setting.

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