Synergism between penicillin G and the antimicrobial ether lipid,rac‐1‐dodecylglycerol, acting below its critical micelle concentration

rac‐1‐Dodecylglycerol (DDG) and penicillin G (Pen G) act synergistically to dramatically lower the minimum inhibitory concentration (MIC) of each other in four Gram‐positive bacteria studied. At one‐half its MIC, DDG ether lowered the MIC of Pen G 10‐ to 80‐fold. Under the same conditions, Pen G lowered the MIC of DDG 4‐ to 7.5‐fold. The critical micelle concentration of DDG was determined to be 7.93 mg/ml (0.0305 mM), which is approximately two‐fold greater than the minimum inhibitory concentration of DDG determined in the presence of a protein‐free chemically defined medium. This finding suggests that DDG is not killing bacteria through its detergent action. Pen G also did not alter the critical micelle concentration of DDG, which indicates that the synergism between these two agents is not related to micelle formation.