Isolation Site Influences Virulence Phenotype of Serotype 14 Streptococcus pneumoniae Strains Belonging to Multilocus Sequence Type 15

Abstract

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 multilocus sequence type (MLST) differed markedly in in vitro and in vivo phenotypes, in accordance with the 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 postchallenge. In spite of these differences, blood and ear isolates were present in the lungs at similar levels at 6 h postchallenge, suggesting that early immune responses may underpin the distinct virulence phenotypes. Transcriptional analysis of lung tissue from mice infected for 6 h with blood isolates versus 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 the differential capacities to elicit early innate immune responses and the distinct virulence phenotypes of clonally related S. pneumoniae strains. Streptococcus pneumoniae (pneumococcus) is one of the foremost bacterial pathogens in terms of global morbidity and mortality. Its disease spectrum includes life-threatening infections such as pneumonia, meningitis, and bacteremia as well as lessserious but highly prevalent infections, including otitis media (OM) and sinusitis. Young children and the elderly are at highest risk, with global estimates of pneumococcal deaths in children under 5 years of age approaching 1 million per year (1). Despite this mortality, S. pneumoniae is a component of the normal microflora of the human nasopharynx. It is estimated that at any given time, approximately 10 to 15% of adults and 25 to 40% of healthy children may be asymptomatically colonized with S. pneumoniae (2). Although only a small fraction of carriers progress to invasive or localized pneumococcal disease, the scale of the denominator results in massive global disease burden.S. pneumoniae is a diverse, genetically plastic species, and the 93 known capsular serotypes are superimposed on Ͼ5,000 sequence types (ST) recognizable by multilocus sequence type (MLST) analysis (3). It has a core genome of roughly 1,500 genes common to all strains, with the remaining 30% of the genome comprising accessory regions (AR) present in some but not all clonal lineages. Individual S. pneumoniae strains differ markedly in their capacity to ca...

Genomic, Phenotypic, and Virulence Analysis of Streptococcus sanguinis Oral and Infective-Endocarditis Isolates

“…Although these studies have provided a critical foundation for our understanding of S. sanguinis physiology, a single strain cannot encompass the full genotypic or phenotypic range of a species. As one example, recent work in Streptococcus pneumoniae, a close relative of S. sanguinis, has highlighted how a small interrogative strain pool can lead to oversimplifications of bacterial functions and host relationships (25)(26)(27). Fortunately, a number of S. sanguinis strains are available with corresponding information, including anatomical origin of isolation (oral cavity of normal subjects or blood of IE patients), multilocus sequence analysis (MLSA) (28), and draft genome sequences (NCBI).…”

In vivo dual RNA-seq reveals that neutrophil recruitment underlies differential tissue tropism of Streptococcus pneumoniae

“…The 4559-Blood-upregulated genes encode proteins involved in multiple pathways such as general metabolism, peroxisome proliferatoractivated receptor (PPAR) signaling, steroid hormone biosynthesis and cAMP signaling. Although both strains belong to the same capsular serotype and ST 6 , our data strongly suggest wildly diverging isolate-specific host responses during early infection, with the rafR SNP varying the host response considerably. Interestingly, the host transcriptional response to 4559M closely resembles that of 9-47-Ear ( Fig.…”

“…However, by 24 h, the ear isolate had been cleared from the lungs, instead spreading to the ear and brain. In contrast, the blood isolate persisted in the lungs at 24 h, but did not spread to the ear or brain 6 . Thus, 6 h post infection is a critical decision point in the pathogenic process, and the similar bacterial loads in the lung at this time enables examination of host/pathogen transcriptional cross-talk without the complication of bacterial dose effects.…”

“…Thus, our findings clearly indicate that modulation of neutrophil recruitment during the early stage of infection plays a key role in the capacity of a given S. pneumoniae strain to persist in the lungs, and the nature of disease ultimately caused by it. Our previous studies have shown that in spite of early clearance from the lung, strains 9-47 Ear and 4559M, expressing the G249 rafR allele, have an enhanced capacity to spread to and/or proliferate in the ear and brain compartments 6,7 . It is not known whether differential carbohydrate metabolism better adapts these strains to available carbohydrate sources in these niches, or whether altered host pro-inflammatory responses contribute to ascension of the Eustachian tube or penetration of the bloodbrain barrier.…”

“…We have previously reported marked differences in virulence in a murine intranasal (IN) challenge model between S. pneumoniae strains belonging to the same serotype and ST, which correlated with clinical isolation site in humans (ear versus blood). In serotype 3 ST180, ST232, and ST233, and in serotype 14 ST15, human ear isolates had greater capacity to cause OM in mice relative to their respective serotype-/ST-matched blood isolates, while blood isolates preferentially caused pneumonia or sepsis in mice, suggesting stable niche adaptation within a clonal lineage 5,6 . Recently we have shown that although the genomes of serotype-/ST-matched blood and ear isolates differ by several single nucleotide polymorphisms (SNPs), the distinct virulence phenotypes correlated with single SNPs in genes encoding uptake and utilization of the sugar raffinose 7 .…”