Infect Immun. 2016 Jul 11. pii: IAI.00416-16. [Epub ahead of print]
One of the least understood aspects of the bacterium Streptococcus pneumoniae (pneumococcus) is its transmission from host-to-host, the critical first step in both the carrier and disease state. To date, transmission models have depended on influenza A co-infection, which greatly enhances pneumococcal shedding to levels that allow for acquisition by a new host. Here, we describe an infant mouse model that can be utilized to study pneumococcal colonization, shedding and transmission during bacterial mono-infection. Using this model, we demonstrate that the level of bacterial shedding is highest in pups infected intranasally at age four days and peaks over the first four days post-challenge. Shedding varied among isolates of five different pneumococcal types. Colonization density was found to be a major factor in the level of pneumococcal shedding and required expression of capsule. Transmission within a litter occurred when there was a high ratio of colonized index to uncolonized contact pups. Transmission was observed for each of the well-colonizing pneumococcal isolates with the rate of transmission proportional to the level of shedding. This model can be used to examine bacterial and host factors that contribute to pneumococcal transmission without the effects of viral co-infection.
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