Cell envelope composition and sensitivity of Proteus mirabilis, Pseudomonas aeruginosa and Serratia marcescens to polymyxin and other antibacterial agents

Two strains of Proteus mirabilis (NCTC 60 and 4199) were consistently more sensitive to antibacterial agents, including methicillin, than were two other strains (NCTC 2896 and 3177). On the basis of minimum inhibitory concentrations, all four strains were resistant to polymyxin, although it has previously been shown that this antibiotic induced some changes in strains 60 and 4199. One of the three strains of Serratia marcescens, the non‐pigmented NCTC 8706, was rather more sensitive to antibacterial agents than the two pigmented strains. Of the four Pseudomonas aeruginosa strains examined, NCTC 10701 tended to be the most sensitive. Chemical analyses of the cell envelopes revealed differences in gross lipid, phospholipid, Mg2+ and 2‐ketodeoxyoctonate (KDO) levels.