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Molecular characterization of Streptococcus pneumoniae isolates recovered from cases of pneumococcal vaccine failure in children under five years of age in the Czech Republic in 2012-2014.

OBJECTIVE
Molecular characterization of Streptococcus pneumoniae isolates recovered in the Czech Republic from previously vaccinated patients diagnosed with invasive pneumococcal disease caused by vaccine serotypes in 2012-2014. The target group were children under five years of age.


MATERIAL AND METHODS
S. pneumoniae strains are referred to the National Reference Laboratory for Streptococcal Infections (NRL) from all over the Czech Republic. Pneumococcal vaccine failure was identified based on the international definition. The NRL routinely performs identification and typing of isolates using both conventional and molecular methods. To characterize in more detail eight isolates from cases of pneumococcal vaccine failure, multilocus sequence typing (MLST) was used.


RESULTS
In 2012-2014, eight S. pneumoniae strains were recovered from children under five years of age diagnosed with vaccine failure. The strains were assigned to serotypes 1 (n = 4), 14 (n = 2), and 3 (n = 2). Serotype 1 isolates were of one sequence type, ST306, which is typical for serotype 1. Similarly, serotype 14 was exclusively of ST124, which is often linked to serotype 14 in the Czech Republic, although in other geographical areas, other STs are often found. Serotype 3 is highly heterogeneous, which is also reflected in multiple STs found in it. We identified a clonal complex comprising ST505 and ST124. ST124 is for the first time reported in S. pneumoniae of serotype 3 in the world.


CONCLUSION
Results are presented of a pilot project conducted in the Czech Republic and focused on molecular characterization of S. pneumoniae strains recovered from cases of pneumococcal vaccine failure in children under five years of age. The data obtained are helpful in improving the surveillance of IPD in the Czech Republic.