Rapid and easy identification of capsular serotypes of Streptococcus pneumoniae by use of fragment analysis by automated fluorescence-based capillary electrophoresis.

The purpose of this study was to develop a high-throughput method for the identification of pneumococcal capsular types. Multiplex PCR combined with fragment analysis and automated fluorescent capillary electrophoresis (FAF-mPCR) was utilized. FAF-mPCR was composed of only 3 PCRs for the specific detection of serotypes 1, 2, 3, 4, 5, 6A/6B, 6C, 7F/7A, 7C/(7B/40), 8, 9V/9A, 9N/9L, 10A, 10F/(10C/33C), 11A/11D/11F, 12F/(12A/44/46), 13, 14, 15A/15F, 15B/15C, 16F, 17F, 18/(18A/18B/18C/18F), 19A, 19F, 20, 21, 22F/22A, 23A, 23B, 23F, 24/(24A/24B/24F), 31, 33F/(33A/37), 34, 35A/(35C/42), 35B, 35F/47F, 38/25F, and 39. In order to evaluate the assay, all invasive pneumococcal isolates (n = 394) characterized at Hospital Sant Joan de Déu, Barcelona, Spain, from July 2010 to July 2011 were included in this study. The Wallace coefficient was used to evaluate the overall agreement between two typing methods (Quellung reaction versus FAF-mPCR). A high concordance with Quellung was found: 97.2% (383/394) of samples. The Wallace coefficient was 0.981 (range, 0.965 to 0.997). Only 11 results were discordant with the Quellung reaction. However, latex reaction and Quellung results of the second reference laboratory agreed with FAF-mPCR for 9 of these 11 strains (82%). Therefore, we considered that only 2 of 394 strains (0.5%) were not properly characterized by the new assay. The automation of the process allowed the typing of 30 isolates in a few hours with a lower cost than that of the Quellung reaction. These results indicate that FAF-mPCR is a good method to determine the capsular serotype of Streptococcus pneumoniae.