Stress response and pathogenicity in Streptococcus pneumoniae

QR180 Immunology

Alsharif, Sultan M M ; Mitchell, Tim

University:University of Glasgow

Department:Institute of Infection Immunity and Inflammation

关键词: streptococcus pneumoniae, oxidative stress, aerobic, anaerobic, microarray, oxygen, virulence;   

Others  :  http://theses.gla.ac.uk/5231/1/2014AlsharifPhD.pdf

来源: University of Glasgow

【 摘 要 】

The pathogen Streptococcus pneumoniae encounters different levels of oxygenduring the infection cycle including colonisation, pneumonia, bateraemia andmeningitis. These different anatomical niches require high levels of genomechanges to sense and respond to those external environmental stimuli. Thebacterial gene expression is known to be affected by oxygen, and it must reactproperly for survival and for developing invasive pneumococcal desiseases (IPDs).Microarray techniques have allowed scanning the whole pneumococcal genomeduring growth in different tensions of oxygen mimicking in vivo conditions. Itwas found that oxygenated growth conditions have significantly elevated severalkey virulence genes. This was further confirmed with qRT-PCR for a selection ofgenes implicated in pathogenicity. Moreover, post-transcriptional stages havebeen also investigated such as protein production, biofilm formation, biologicalactivities and adherence assays for several virulence factors performed underthe effect of presence or absence of oxygen.The data illustrate that 420 out of 2,236 genes (17 % of the entire TIGR4genome) were differentially expressed in the presence of oxygen compared to itsabsence. 262 genes (11 %) were over-expressed when pneumococci were grownin oxygenated conditions relative to transcriptional profile in anaerobic growthconditions, indicating the magnitude of roles played by oxygen on pneumococcalgene expression. Anaerobic growth of TIGR4 showed down-regulation of 158genes (7 %). Oxygen modulates induction of ply, pspC and other seven genesinvolved in pili structuring subunits (rlrA, rrgA, rrgB and rrgC) and assemblingenzymes (srtB, srtC and srtD). This may suggest that the pneumococcalpopulation grown under atmospheric environment is equipped with greatercapability to progress IPDs compared to anaerobically grown bacteria. Inaddition to this, pneumococcal adhesion in vitro for TIGR4 grown in oxygenatedor anaerobic growth conditions revealed a significant increase in those grown inoxygenated growth conditions, indicating that oxygen may play a key role inbacterial-host attachment. Interestingly, ablation of pspC has resulted in similaradhesion percentages of TIGR4 grown under both conditions, oxygenated andanaerobic.Furthermore, several genes involved in metabolism were up-regulated inoxygenated environment, particularly transporters, which are considered highlyimportant for a bacterium that lacks an electron transport chain, catalase andtricarboxylic acid. Additionally, the results showed phenotypic characterisationand changes in cells morphology from pneumococcal growth curves for severalstrainswith different genome backgrounds grown under different levels ofoxygen concentrations. Further investigation of the pathogen biology revealeddifferences in pneumolysin production and activity.These findings highlight that virulence genes expression is induced once themicro-organism is exposed to oxygenated environment, and data analysis hasdemonstrated potential links between pneumococcal metabolism and theirability to cause diseases.