Comparison of Four Methods for Streptococcus pneumoniae Capsular Typing

Pneumococcal capsular-type identification is essential for monitoring the epidemiology of pneumococcal infections and for establishing the effectiveness of pneumococcal vaccines. The objective of this work was to compare the accuracy of four methods of Streptococcus pneumoniae capsular typing.

A prospective blind study was carried out at Donostia University Hospital (northern Spain) to determine the capsular types of 50 pneumococcal clinical isolates using four techniques: a) S. PneumoStripTM: a reverse-hybridization strip-based commercial assay that detects 76 pneumococcal serotypes: 42 individually and 34 in pairs. b) FAF-mPCR: a single-step multiplex-PCR (polymerase chain reaction) assay combined with fragment analysis using automated fluorescent capillary electrophoresis, which can differentiate 92 serotypes in a single tube: 31 individually, 28 in pairs, and 33 in groups of 3 to 5 serotypes. c) PCRSeqTyping: which enables the detection of 91 serotypes after sequencing the regions of the cpsB gene in two steps: 59 directly and the remaining 32 serotypes in a second step. d) The Quellung reaction.

The S. PneumoStripTM, FAF-mPCR and PCRSeqTyping identified the serotypes of all the 50 clinical isolates. With the Quellung reaction 46/50 (92%) isolates were correctly serotyped. The quickest technique was the S. PneumoStripTM, followed by the single-step multiplex PCR assay and PCRSeqTyping. The Quellung reaction was the slowest technique.

The S. PneumoStripTM, PCRSeqTyping, and FAF-mPCR were very accurate techniques for pneumococcal serotyping, with S. PneumoStripTM obtaining results more rapidly. The combination of any of these S. pneumoniae molecular typing techniques and the Quellung reaction as confirmation reference method is a highly precise and fast strategy for the serotyping of high number of pneumococcal clinical isolates.