Boron-containing antibacterial agents: effects on growth and morphology of bacteria under various culture conditions

The effects of a number of synthetic antibacterial agents of the borinic acid and diazaborine types on the growth of enteric bacteria were examined. In minimal medium aerobic growth was immediately slowed; slow nonexponential growth continued for an extended period, and the cells remained viable. The effect was also seen in anaerobic cultures and was not antagonized by a number of common nutrients, vitamins, or growth factors. The response was modified by the addition of casein hydrolysate to the medium. This seemed to be a nutritional effect dependent principally on lysine and leucine. The modified response consisted of a period of abnormal growth lasting for at least one doubling time after the addition of the antibacterial agent. The turbidity at first increased more rapidly than that of the controls and was approximately equal to that of the controls after 30 min. However, the increase in bacterial mass (dry weight) was only 0.75 of the amount predicted by the change in turbidity. The viable count increased in proportion to the turbidity. Changes in the cell envelope were revealed by electron microscopy and by an alteration in the response of cells to lytic agents. After the period of abnormal growth cultures entered a premature stationary phase.