Population Biology of Streptococcus pneumonia in West Africa: Multi-locus Sequence Typing of Stereotypes That Exhibit Different Predisposition to Invasive Disease and Carriage
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Date
2013
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Public Library of Science
Abstract
Background: Little is known about the population biology of Streptococcus pneumonia in developing countries, although the majority of pneumococcal infections occur in this setting. The aim of the study was to apply MLST to investigate the population biology of S. pneumonia in West Africa. Methods: Seventy three invasive and carriage S. pneumonia isolates from three West African countries including The Gambia, Nigeria and Ghana were investigated. The isolates covered seven stereotypes (1, 3, 5, 6A, 11, 14, 23F) and were subjected to multi-locus sequence typing and antibiotic susceptibility testing. Results: Overall, 50 different sequence types (STs) were identified, of which 38% (29) were novel. The most common ST was a novel clone-ST 4012 (6.5%), and some clones including STs 913, 925, 1737, 2160 and 3310 appeared to be specific to the study region. Two STs including ST 63 and ST 4012 were associated with multiple stereotypes indicating a history of stereotype switching. ST 63 was associated with stereotypes 3 and 23F, while ST 4012 was associated with stereotypes 6A and 23. eBURST analyses using the stringent 6/7 identical loci definition grouped the 50 STs into 5 clonal complexes and 65 singletons, expressing a high level of genetic diversity among the isolates. Compared to the other stereotypes, stereotypes 1 and 5 isolates appeared to be more clonal. Internationally recognized antibiotic resistant clones of S. pneumonia were generally absent in the population investigated and the only multi-drug resistant isolate identified (1/66) belong to the Pneumococcal Epidemiology Network clone ST 63. Conclusions: The pneumococcal population in West Africa is quite divergent, and stereotypes that are common in invasive disease (such as stereotypes 1 and 5) are more likely to be clonal than stereotypes that are common in carriage.