Streptococcus pneumoniae is a common but potentially deadly bacterium with a genetic population that has been shifting and changing globally, particularly since the introduction of the childhood vaccine 7vPCV (7-valent pneumococcal conjugate vaccine) 1. Due to changes in the genome, S. pneumoniae has the ability to become immune to the 7vPCV 2. This is a worrisome problem particularly for children worldwide for whom a large number of diseases are caused by pneumococci 1. Genotyping techniques have been implemented to further understand the genetics of pneumococci however current 'gold standard' methods are laborious and expensive 3. An alternative genotyping method MLVA (Multi-Locus Variable-Number of Tandem Repeat Analysis) is reported to be more discriminatory, faster and cheaper 3. Recently a 13vPCV was introduced into the Australian National Immunisation Schedule in July 2011, replacing the 7vPCV in an effort to combat increasing pneumococcal diseases 4. There have been no publications examining the pneumococcal genetic population structure in Australia since the introduction of the 13vPCV.
This study aims to determine the optimal MLVA targets to genotype invasive S. pneumoniae in Queensland and determine the pneumococcal population structure, enabling the detection of possible serotype replacement and/or capsule switching events. Three sets of MLVA methods using different oligonucleotide primers for MLVA genes have been published and were used to genotype invasive isolates of S. pneumoniae causing diseases in Queensland children 15 years or younger from 2007-2012 35 67.
A total of 317 isolates were genotyped using each of the three sets of MLVA methods and 186 isolates were genotyped using the 'gold standard' MLST (Multi-Locus Sequence Typing). MLVA was proven to be faster, cheaper and more discriminatory than MLST. There is evidence of diversification of the pneumococcal population structure since the introduction of 13vPCV and evidence for potential capsule switching, which allows the pneumococci to evade the vaccine. The findings of this study will be added to the Australian and international pneumococcal epidemiological databases.