Cell composition and drug resistance in Escherichia coli

Resistance of micro-organisms to antibacterial drugs which cannot be attributed to a genetic change may often be traced to phenotypic changes in cell composition caused by differing growth conditions. To investigate an aspect of this attribute E. coli NCTC 86 was grown on a simple synthetic media containing alanine or cystine and, as a control, in nutrient broth. Cells grown on the media containing alanine and cystine showed a depleted total extractable lipid and phospholipid content. Phosphatidylethanolamine was notably reduced in both cases. Electrophoretic studies revealed a reduction in the surface lipid of cells grown on the simple synthetic media, while electron microscopy revealed defects in the cell wall of the cells grown on alanine. The total protein content of cells grown on alanine was reduced, whereas cells grown on the cystine showed an enhanced total carbohydrate content. Lipopolysaccharide synthesis was possibly also affected as judged by 2-keto-3-desoxy-D-manno-octonic aid content. The action of p-tertiary amylphenol, cetrimide and polymyxin B sulphate, showed that cells grown on the media containing alanine were most susceptible to the action of the phenol and cetrimide, whilst cells grown on the media containing cystine were most resistant to the action of polymyxin.