Abstract
BackgroundStreptococcus pneumoniae can be carried asymptomatically in the nasopharynx of its human host but can also cause a wide range of infections. A role for pneumococcal phase variants in the different lifestyles of this bacterium has been suggested but no systematic survey of the colony phenotypes of isolates associated with human infections has been undertaken.ResultsWe report the colony opacity phenotypes of a genetically diverse set of 304 invasive isolates representing 10 serotypes. Over half of the isolates (52%) presented the opaque phenotype whereas transparent variants accounted for only 26% of the total. However, the frequency of recovery of each phase variant was not uniform, while serotypes 1, 4, 12B and 23F presented the opaque phenotype more frequently than expected by chance, serotypes 3 and 14 where less frequently associated with this phenotype.ConclusionThe opaque phenotype was the most frequent phenotype found among invasive isolates. An unexpected and equally important finding is the variability of the dominant opacity phenotype found among serotypes. This observation highlights the heterogeneity of opacity phenotypes in invasive isolates and lends further support to the proposal that other factors, in addition to the site of isolation, determine the opacity phenotype of a given isolate. The association between serotype and colonial opacity could help explain epidemiological differences observed among pneumococcal serotypes such as a higher invasive disease potential.
Highlights
Streptococcus pneumoniae can be carried asymptomatically in the nasopharynx of its human host but can cause a wide range of infections
The only habitat identified for Streptococcus pneumoniae is the human host where the bacterium is able to persist and multiply, either asymptomatically in the mucosal surface of the nasopharynx or being responsible for infections that range from milder manifestations such as otitis media to life threatening infections such as bacteremia
Colony morphology and relationship with serotype Isolates representing the serotypes tested and the phenotypes found are shown in figure 1 and in additional file 1
Summary
Streptococcus pneumoniae can be carried asymptomatically in the nasopharynx of its human host but can cause a wide range of infections. A role for pneumococcal phase variants in the different lifestyles of this bacterium has been suggested but no systematic survey of the colony phenotypes of isolates associated with human infections has been undertaken. The only habitat identified for Streptococcus pneumoniae (pneumococcus) is the human host where the bacterium is able to persist and multiply, either asymptomatically in the mucosal surface of the nasopharynx or being responsible for infections that range from milder manifestations such as otitis media to life threatening infections such as bacteremia. A phenomenon of intrastrain phase variation in the colonial opacity of the pneumococcus has been identified and related to increased survival in each of these habitats [1]. A recent report proposes a more complex role for phase variation in the biology of (page number not for citation purposes)
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