Detection of pneumococcus by PCR

Abstract

New rapid methods for sensitive and specific detection of pneumococci are not only needed to improve the diagnosis of pneumococcal disease but are also essential for vaccine and carriage studies. The purpose of this study was to develop sensitive PCR methods for the detection and quantification of S. pneumoniae and to study the applicability of these methods to detecting pneumococci in clinical samples.

A previously described PCR method was first developed further by introducing a Europium-labelled hybridisation probe for the detection of amplification products. The hybridisation method was easy to use and improved the specificity of the PCR assay. The developed PCR assay was established as a sensitive method for detecting pneumococcal DNA when the presence of pneumococcal DNA in over 2500 middle ear fluid (MEF) samples of children with acute otitis media (AOM) was studied by using the method. Pneumococcal findings increased by 76% when using PCR detection in addition to culture, compared to using culture alone. However, the PCR-positive, culture-negative AOM events represented a less severe type of disease compared to the culture-positive events. A positive PCR finding seems to indicate the presence of viable, although often non-culturable pneumococci within the middle ear cleft.

To be able to rapidly detect and quantify the initial numbers of pneumococcal genome copies in clinical samples, a real-time PCR method for the detection and quantification of pneumococcal DNA was developed. In real-time PCR, amplification and detection of amplification products occur simultaneously, which makes it possible to monitor the phase of the reaction at a particular stage or continuously. The method developed here was applied to the analysis of MEF samples and to investigating the nasopharyngeal carriage of pneumococcus. The sensitivities of bacterial culture and real-time PCR in detecting pneumococci were also compared. The real-time PCR assay was found to be rapid and sensitive and to provide information about the differences between the numbers of bacteria in samples. However, the quantitative results were shown to be dependent on the DNA extraction method applied. The real-time PCR method developed appears to be a good aid in research where an accurate and sensitive pneumococcal diagnosis is needed.