Genome-Wide Identification of Genes Essential for the Survival of Streptococcus pneumoniae in Human Saliva

Abstract

Since Streptococcus pneumoniae transmits through droplet spread, this respiratory tract pathogen may be able to survive in saliva. Here, we show that saliva supports survival of clinically relevant S. pneumoniae strains for more than 24 h in a capsule-independent manner. Moreover, saliva induced growth of S. pneumoniae in growth-permissive conditions, suggesting that S. pneumoniae is well adapted for uptake of nutrients from this bodily fluid. By using Tn-seq, a method for genome-wide negative selection screening, we identified 147 genes potentially required for growth and survival of S. pneumoniae in saliva, among which genes predicted to be involved in cell envelope biosynthesis, cell transport, amino acid metabolism, and stress response predominated. The Tn-seq findings were validated by testing a panel of directed gene deletion mutants for their ability to survive in saliva under two testing conditions: at room temperature without CO2, representing transmission, and at 37°C with CO2, representing in-host carriage. These validation experiments confirmed that the plsX gene and the amiACDEF and aroDEBC operons, involved in respectively fatty acid metabolism, oligopeptide transport, and biosynthesis of aromatic amino acids play an important role in the growth and survival of S. pneumoniae in saliva at 37°C. In conclusion, this study shows that S. pneumoniae is well-adapted for growth and survival in human saliva and provides a genome-wide list of genes potentially involved in adaptation. This notion supports earlier evidence that S. pneumoniae can use human saliva as a vector for transmission.

Streptococcus pneumoniae: transmission, colonization and invasion

“…S. pneumoniae can also be easily cultured from common objects, such as soft toys recently handled by colonized children 20 . Under ambient, nutrient-sufficient conditions, such as in ex vivo human saliva, pneumococci can survive for days 21 . Under nutrient-poor conditions, such as in airway surface fluid, bacterial expression of Ply increases ex vivo survival 16 .…”

The role of pathogen genomics in assessing disease transmission

“…27 Furthermore, the genomewide analysis of Streptococcus pneumoniae identified 147 genes needed for survival in human saliva and transmission by droplet spread, including those involved in cell envelope synthesis and cell transport. 28 On an entirely different time scale, the sequencing of Yersinia pestis bacteria isolated from teeth disinterred from the east Smithfield Black Death burial ground in London dating to 1348 showed that the plague strains associated with this pandemic were similar to those currently circulating, although associated mortality was far greater. 29 This is compatible with the idea that the high mortality seen in the medieval plagues (and the sixth century Plague of Justinian 30 ) was more likely to be associated with epidemiological circumstances (overcrowding, poor general health and living conditions) than with bacterial encoded virulence.…”

Bacterial peptide transporters: Messengers of nutrition to virulence

“…48 Genome wide Tn-seq screen revealed that S. pneumoniae requires its peptide transport system AmiACDEF for survival in human saliva, an essential strategy for transmission. 49,50 Regulation of transcription of the adherence mediating cell surface polypeptide CshA by hexa-hepta peptide permease HppA in S. gordonii shows another example. 51 The Gram positive cocci, S. agalactiae, responsible for causing major invasive infection in human newborns, requires 4 peptide permeases for attachment to the host cells and to express its virulence determinants.…”