Quorum-Sensing Systems LuxS/AI-2 and Com Regulate Streptococcus pneumoniae Biofilms in a Bioreactor with Living Cultures of Human Respiratory Cells

Infect Immun. 2013 Apr;81(4):1341-53.

S. Chochua, J. Concepcion-Acevedo, K. P. Klugman and J. E. Vidal

Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA. jvidalg@emory.edu


Streptococcus pneumoniae is an important commensal and pathogen annually responsible for almost a million deaths in children under five years of age.   S. pneumoniae colonizes the nasopharynx and can spread to other anatomic sites causing otitis media, pneumonia, bacteremia and meningitis.  Biofilm formation is important for both colonization and pathogenesis; however, production and regulation of biofilms formed on human cells have not been fully investigated.  To study the production and regulation of S. pneumoniae biofilms (SPB) we developed a bioreactor with living cultures of human respiratory epithelial cells (HREC) and a continuous flow of nutrients, simulating the environment of the human respiratory epithelium.  SPB were also formed under static conditions on immobilized HREC. Using the bioreactor and immobilized cell cultures, we identified two quorum-sensing (QS) regulators of early SPB production, Com and LuxS/autoinducer 2 (AI-2).  While LuxS/AI-2 regulated SPB on abiotic surfaces and HREC, Com specifically regulated early biofilm formation on human cells. Mutations in either comC or luxS rendered S. pneumoniae unable to form early biofilms on HREC. Nevertheless, biofilm biomass of strain D39-derivative ∆comC and ∆luxS QS mutants were restored by genetic complementation.  Biofilms formed on immobilized HREC and incubated under static conditions were completely lysed 24 h post-inoculation. Biofilm autolysis appears to be controlled by these two quorum-sensing mechanisms.  Our studies also revealed that invasive pneumococcal strains produced more early biofilms on lung cells than on pharyngeal cells. This study is the first report of biofilms produced on human respiratory cells and biofilm autolysis mediated by QS.

PMID: 23403556


Sopio Chochua-pic


S. pneumoniae biofilms formed on human respiratory epithelial cells (HREC):

(A) Diagrammatic representation (not to scale) of organized pneumococcal biofilms at early stages of biofilm development on HREC (left image). (i) Fluorescent microscopy of pneumococcal biofilms (green), strain D39 expressing GFP, on lung cells. Nuclei were stained with TOPRO-3 (blue). (ii) Scanning electron microscopy of pneumococcal biofilms (strain D39) grown on human lung cells for 8 h.

(B) Proposed QS-regulated mechanisms of early formation of S. pneumoniae biofilms .


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