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Bacteria can become insensitive to antibiotics by picking up resistance genes from the environment. Unfortunately for patients, the stress response induced by antibiotics activates competence in microorganisms, the ability to take up and integrate foreign DNA. Microbiologists from the University of Groningen (UG) and the University of Lausanne have now described a new mechanism by which Streptococcus pneumoniae can become competent, and why biofilms may be important in this process. Their results were published in Cell Reports on November 27.
UG Ph.D. student Jelle Slager first described the mechanism of competence four years ago. Subsequently, his colleague Arnau Domenech, a team member from the Veening lab at the University of Lausanne, who is the first author of the Cell Reports paper, screened a large number of clinically relevant substances for their ability to induce competence. Two drugs stood out: aztreonam and clavulanic acid, which are both used to fight infections. "But when we looked closer, they didn't affect competence through a known mechanism," says Slager. "So we investigated what was going on."
Competence - Release - Competence - Peptide - CSP
Competence is induced through the release of competence stimulating peptide (CSP). Cells secrete this peptide when they experience stress, for example, when they are challenged with certain antibiotics. Only when the CSP concentration around them reaches a certain threshold do the cells become competent. "This is a process called quorum sensing, which elicits a response once enough cells are affected." As CSP is secreted into the environment, all cells become competent at more or less the same time.
However, something different happened with the Streptococcus pneumoniae cells used in this study. Slager says, "As these cells divide, they normally form mother-and-daughter pairs. But in response to these two drugs, they start forming longer chains, as the cell division mechanism is affected by the drugs. When cells in these chains secrete CSP,...
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