Effect of osmolality on the response of Escherichia coli to mecillinam

The influence of osmolality on the effect of the novel beta-lactam antibiotic, mecillinam, on Escherichia coli was examined in a turbidimetric system. Both sucrose and sodium chloride were able to protect E. coli from the effects of mecillinam during the stage of conversion to morphologically abnormal forms, and the additional presence of small amounts of magnesium sulfate protected the spherical forms from subsequent lysis. More phenotypically "resistant" survivors were recovered in osmotically protective media than in broth of low osmolality. Sucrose appeared a better protective agent than sodium chloride, but growth of the phenotypically resistant population was much slower in the sucrose-containing than in sodium chloride-containing medium.