Infect Immun. 2015 Sep 28. pii: IAI.01081-15. [Epub ahead of print]

Isolation Site Influences Virulence Phenotype of Serotype 14 Streptococcus pneumoniae Strains Belonging to ST15.

Amin Z1, Harvey RM1, Wang H1, Hughes CE1, Paton AW1, Paton JC1, Trappetti C2.

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Streptococcus pneumoniae is a diverse species causing invasive as well as localized infections that result in massive global morbidity and mortality. Strains vary markedly in pathogenic potential, but the molecular basis is obscured by the diversity and plasticity of the pneumococcal genome. We have previously reported that S. pneumoniae serotype 3 isolates belonging to the same multi-locus sequence type (MLST) differed markedly in in vitro and in vivo phenotype, in accordance with clinical site of isolation, suggesting stable niche adaptation within a clonal lineage. In the present study we have extended our analysis to serotype 14 clinical isolates from cases of sepsis or otitis media that belong to the same MLST (ST15). In a murine intranasal challenge model, five ST15 isolates (three from blood and two from ears) colonized the nasopharynx to similar extents. However, blood and ear isolates exhibited significant differences in bacterial loads in other host niches (lungs, ear and brain) at both 24 and 72 h post challenge. In spite of these differences, both blood and ear isolates were present in the lungs at similar levels at 6 h post challenge, suggesting early immune responses may underpin the distinct virulence phenotypes. Transcriptional analysis of lung tissue from mice infected for 6 h with blood vs ear isolates revealed 8 differentially expressed genes. Two of these were exclusively expressed in response to infection with the ear isolate. These results suggest a link between differential capacity to elicit early innate immune responses and the distinct virulence phenotypes of clonally-related S. pneumoniae strains.

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PMID: 26416904 [PubMed - as supplied by publisher]