> PCR Deduction of Pneumococcal Serotypes
PCR Deduction of Pneumococcal Serotypes
Accurate serotyping is essential for epidemiologic study of Streptococcus pneumoniae. We have devised simple multiplex PCRs schemes to reliably deduce specific pneumococcal serotypes from isolate sets and also from clinical specimens. Overall, we have found this PCR approach to be highly reliable, with the potential to greatly reduce reliance upon conventional serotyping. We feel that this system will give serotype-determining potential to any facility that lacks the expensive typing sera and other reagents needed for conventional serotyping, yet has the modest equipment necessary for DNA amplification and electrophoresis.
When using PCR for deduction of invasive pneumococcal serotypes it is important to realize that the serotype distribution of invasive S. pneumoniae has changed drastically since introduction of the 7 valent conjugate vaccine. See serotype distribution of invasive pneumococcal disease isolates among children <5 years of age, Active Bacterial Core surveillance areas, 2008 vs. 1998-1999 
[PPT - 220 KB] (Updated Oct 2009). It is important to realize that this figure does not depict disease incidence rate, only cumulative serotype proportions among our total isolates.
Relevant publications where we have employed multiplex PCR based serotyping.
- Sequential multiplex PCR for S. pneumoniae serotyping. (Pai R, et. al., J Clin. Microbiol. 44:124-131, 2006).
- Sequential multiplex PCR for identifying pneumococcal capsular serotypes from South-Saharan African clinical isolates. (Morais L, et al., J Med Microbiol. 56:1181-4, 2007).
- Sequential multiplex PCR for determining capsular serotypes of pneumococci recovered from Brazilian children. (Dias CA, et al., J Med Microbiol. 56:1185-8, 2007).
- PCR-based quantitation and clonal associations of the current prevalent invasive serogroup 6 pneumococcal serotype, 6C, in the United States: 1999, 2006 – 2007. (Carvalho MdG, et al., J Clin Microbiol. 47:554-559, 2009).
- Rarely occurring 19A-like cps locus from a serotype 19F pneumococcal isolate indicates continued need of serology-based quality control for PCR-based serotype deduction. (Pimenta FC, et al., J Clin Microbiol. Published online ahead of print. 2009.)
PCR Serotype Deduction Protocols
It is important to realize that although we validate our primer sets thoroughly through using diverse isolate sets representing individual serotypes, we will continue to refine the scheme. This will involve adding serospecificities and updating primer sets to improve specificity. Consult our current updated primer list (40 serospecificities) (see first bullet / link below).
There are 2 important points to keep in mind using this PCR serotyping scheme:
- Band sizes must exactly match those of positive controls before assigning a serotype. We have occasionally detected non-specific bands when multiplex PCR testing clinical specimens.
- The positive pneumococcal control band for cpsA is negative in 1-2% of PCR-serotypeable isolates that we have encountered. We have found this result most often in serotypes 25 and 38, but have also rarely encountered this result for serotypes 14 and 35A. The bottom line is that at present a negative cpsA control does not necessarily equate to a non-serotypeable isolate or a pneumococcus-negative clinical specimen.
- List of oligonucleotide primers used for pneumococcal serotype deduction
[PDF - 86KB] (NEW May 2009) - Fast Extraction of DNA for Streptococcal culture isolates [PDF - 12KB] (NEW May 2009)
- Blood and Body Fluid DNA Extraction for Streptococci [PDF - 30KB] (NEW May 2009)
The following 3 schemes are useful for deducing serotypes from pneumococcal isolates:
- U.S. - Multiplex PCR for deducing serotypes from pneumococcal isolates
[XLS - 554KB] (NEW May 2009) - Africa - Sequential Multiplex PCR for identifying pneumococcal capsular serotypes from south-Saharan African clinical isolates [PPT - 500KB] (NEW May 2009)
- Latin America - Sequential Multiplex PCR for determing capsular serotypes of pneumococci recovered from Brazilian children [PPT - 785KB] (NEW May 2009)
We have found the following sequential PCR scheme useful for determining pneumococcal serotypes from sterile-site clinical specimens. Please make sure that band sizes exactly match those of positive controls before assigning a serotype, since we have occasionally detected non-specific bands when multiplex PCR testing clinical specimens.
- Protocol for Multiplex PCR ‐ S. pneumoniae Serotype Deduction of 40 specificities (for
clinical specimens) [PDF - 562KB] (NEW May 2009)
Deducing serotypes from nasopharyngeal specimens. COMING SOON!