Genetic Diversity of the Pneumococcal Capsule: Implications for Molecular-based Serotyping

Mary Catherine McEllistrem


Future Microbiol. 2009;4(7):857-865. 

In This Article

Additional Limitations of Molecular-based Assays

As the capsular serotype is ascertained by a portion of the capsular operon, it is possible that the amplified fragment would not correlate with the rest of the operon. Specifically, a strain that has a point mutation in one capsular gene could result in a nonfunctional capsular operon. For example, a serotype 3 biofilm-derived rough variant with a SNP in the cps3D gene produces minute amounts of capsule;[38] however, a PCR-based assay would likely classify this as a serotype 3 strain. Likewise, a strain with an unusual sequence in an amplified fragment of a presumed 'type-specific gene' may result in misclassification. For example, a serotype 19F strain by quellung reaction was repeatedly misclassified as serotype 19A using amplification of both the mnaA and wzy genes (Table 2).[20] These aforementioned scenarios clearly indicate with absolute certainty that the quellung reaction must continue to be performed despite prior validation of any molecular-based serotyping method.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as: