Historical development of typing methods for Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae is a major cause of morbidity and mortality in developing countries, especially in children, even though this is a vaccine-preventable disease. Several vaccines are available for which programmes are in regular immunization, but the success of this depends upon their efficacy and vaccine coverage of the serotypes prevalent in the region. A so-called replacement phenomenon has made it mandatory that there should be a regular and continuous survey of serotype prevalence whenever the vaccine is used. Many typing methods have been described including serology as well as molecular-based typing. We have analysed most of the described typing methods for pneumococcal isolates and discussed their prospects for future surveillance programmes. In brief, molecular typing such as sequential multiplex PCR is more reliable for typing, but it has limitations as it types the isolates only up to serogroup level in few cases, and therefore is still dependent on conventional serotyping methods like Quellung and co-agglutination. However, conventional typing methods are limited because of cross-reactivity with other serotypes within serogroups. Conventional serological methods are costly, labour-intensive, and prone to misidentification, whereas current DNA-based methods have limited serotype coverage requiring multiple PCR primers. Implementation of pneumococcal conjugate vaccines necessitates continued monitoring of circulating strains to consider vaccine effectiveness and subsequent substitution of serotypes.