Spontaneous polymyxin-resistant mutants of Pseudomonas aeruginosa were isolated. The
mutations responsible for this phenotype were mapped to a two-component signal
transduction system similar to PmrAB of Salmonella enterica serovar Typhimurium. Lipid A
of these mutants contained aminoarabinose, an inducible modification that is associated
with polymyxin resistance. Thus, P. aeruginosa possesses a mechanism that induces
resistance to cationic antimicrobial peptides in response to environmental conditions.