What is quorum sensing and why is it important in bacterial pathogenesis?

• A. A communication system using signaling molecules that regulate gene expression in response to population density, often controlling virulence and biofilm formation.
• B. A mechanism for bacteria to move toward chemical attractants during chemotaxis.
• C. A process by which bacteria produce spores under stress.
• D. A method by which bacteria exchange plasmids during conjugation.

Answer: (A)

Quorum sensing is a communication system in bacteria that uses signaling molecules to gauge population density and regulate gene expression accordingly. As numbers of bacteria increase, these signaling molecules accumulate; when a threshold is reached, receptors detect the signal and switch on or off groups of genes, often including virulence factors and biofilm formation. This coordinated control lets pathogenic bacteria act in a concerted way, expressing toxins, adhesion factors, and protective biofilms only when enough cells are present, which enhances colonization, persistence in the host, and resistance to treatment. Other processes like chemotaxis toward chemicals, sporulation under stress, or plasmid transfer during conjugation are distinct mechanisms and not the same as quorum sensing.