Antibiotics as Signal Molecules

The increasingly frequent failure of some of the antibiotics to control many previously treatable infections has led to the investigation of the mechanisms responsible for such resistance. The production of antibiotics commonly occurs when cells reach stationary phase, and often, relatively high cell densities are required for robust antibiotic production. Bacteria count population members in a quorum-sensing process by releasing self-produced signaling molecules or autoinducers (AI) that accumulate externally. When the autoinducing molecules accumulate in the medium above a certain threshold, they trigger the quorum-sensing response. The acyl homoserine lactones (AHL) are an important class of autoinducers that contain structural differences in their aliphatic tails in Gram-negative bacteria. Cell signaling and cell density are especially important in the formation of tightly packed, spatially organized biofilms. These bacterial communities are often attached to surfaces and encased in an extracellular matrix normally produced by the bacteria themselves.