Functional Characterisation of TprA/PhrA Quorum Sensing System in Streptococcus pneumoniae

Quorum-sensing (QS) mechanisms are pivotal for microbial adaptation to host environments, and often required for pathogenesis without affecting bacterial vitality. Hence targeting QS diminish the fitness cost of inhibition, and the emergence and spread of antibiotic resistance. I characterized the TprA/PhrA QS system in the important human pathogen Streptococcus pneumoniae with a view to target its operation using novel soluble linear molecularly imprinted polymers (LMIP). I found that TprA/PhrA system is commonly found in pneumococcal strains, and is required for mucin, galactose and mannose utilisation. On galactose, TprA is an activator of the virulence determinant neuraminidase (nanA), and controls the expression of nine different operons on galactose and mannose. tprA and phrA mutants are highly attenuated in the mouse model of pneumonia and septicemia, and in the chinchilla model of otitis media, indicating that the TprA/PhrA system is a major virulence determinant and a highly relevant anti-infective target. To interfere with the operation of TprA/PhrA, I used, for the first time, highly homogenous soluble LMIP specific to the PhrA peptide. LMIP decreased PhrA-induction in a dose-dependent and sequence-specific manner, and possessed no visible toxicity in the murine model. It was also shown that LMIP were protective against lethal pneumococcal challenge. This study sets the stage for studies on a novel class of drugs to target Gram positive pathogens.