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

Mary Catherine McEllistrem

Disclosures

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.

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