INVESTIGATION OF SEROTYPE 19F wzy VARIANT AMONG CLINICAL STREPTOCOCCUS PNEUMONIAE ISOLATES IN KOREA

Accurate identification of Streptococcus pneumoniae serotypes 19A and 19F is important because these serotypes are predominant in invasive pneumococcal disease and are closely associated with multi-drug resistance, especially in Asia. Although the Quellung assay is accepted as the gold standard in S. pneumoniae serotyping, its high cost and labor intensive procedures has led to adoption of sequential multiplex (SM)-PCR of S. pneumoniae. However, the existence of a 19F wzy variant with its close genetic similarity to 19A wzy has given rise to falsenegative 19F and false-positive 19A serotyping. Hence, the study employed a 19F wzy variant-specific primer set in a PCR-based identification among 378 S. pneumoniae clinical isolates previously serotyped using SM-PCR and Quellung assays. Although 112 of 378 isolates showed positive results by 19Fvar primer set, no 19F wzy variant obtained when they were confirmed by SM-PCR and Quellung assay. Among 8 SM-PCR nontypeable serotypes, none could be confirmed as being serotype 19F wzy variant. Thus the reliance on the PCR using 19Fvar primer set to detect S. pneumoniae 19F wzy variant is subject to high frequency of false positive results and should be confirmed by the Quellung assay. Based on these results, S. pneumoniae 19F wzy variant was not detected yet in this study from Korea.