Influence of specific growth rate and nutrient-limitation upon the sensitivity of Escherichia coli towards polymyxin B.

The sensitivity of Escherichia coli to the lytic action of polymyxin B was assessed for cells grown in a chemostat at a variety of specific growth rates and under conditions of carbon, nitrogen, phosphorus and magnesium limitation. Magnesium and phosphorus limited cells demonstrated a trend of increased resistance with increasing growth-rate, whereas carbon and nitrogen limited cells increased their sensitivity as the growth rate increased. Divergent patterns of sensitivity, such as these, allowed a number of models for resistance towards polymyxin to be assessed. It was not possible to attribute polymyxin sensitivity to any single envelope component; rather the patterns of sensitivity reflect, in a complex manner, presence of envelope proteins and acidic phospholipids.