Meningitis pathogens evade immune responses by thermosensing

Bacterial meningitis is a major cause of death and disability in children worldwide. Two human restricted pathogens, Streptococcus pneumoniae and Haemophilus influenzae, are the major causative agents of bacterial meningitis, attributing to 200,000 deaths annually. These pathogens are often part of the nasopharyngeal microflora of healthy carriers. However, what factors elicit them to disseminate and cause invasive diseases remain unknown. Elevated temperature and fever are hallmarks of inflammation triggered by infections and can act as warning signal to these pathogens. Here, we investigate whether these pathogens could sense environmental temperature to evade host complement-mediated killing. We show that expression of two vital virulence factors and vaccine components, the capsule and factor H binding proteins, are temperature dependent. We identify and characterize four novel RNA thermosensors in S. pneumoniae and H. influenzae within their 5′-untranslated regions of genes, responsible for capsular biosynthesis and production of factor H binding proteins. Our data further demonstrate that these pathogens have co-evolved thermosensing abilities independently with unique RNA sequences, but distinct secondary structures, to evade the human immune system.Author SummaryStreptococcus pneumoniae and Haemophilus influenzae are bacteria that reside in the upper respiratory tract. This harmless colonization may progress to severe and often lethal septicaemia and meningitis, but molecular mechanisms that control why these pathogens invade the circulatory system remain largely unknown. Here we show that both S. pneumoniae and H. influenzae can evade complement killing by sensing the temperature of the host. We identify and characterize four novel RNA thermosensors in S. pneumoniae and H. influenzae within their respective 5′-untranslated regions of genes, influencing capsular biosynthesis and production of factor H binding proteins. Moreover, we show that these RNA thermosensors evolved independently with exclusive unique RNA sequences to sense the temperature in the nasopharynx and in other body sites to avoid immune killing. Our finding that regulatory RNA senses temperatures and directly regulate expression of two important virulence factors and vaccine components of S. pneumoniae and H. influenzae, is most important for our understanding of bacterial pathogenesis and for vaccine development. Our work could pave the way for similar studies in other important bacterial pathogens and enables clinicians and microbiologists to adjust their diagnostic techniques, and treatments to best fit the condition of the patients.