. Author manuscript; available in PMC: 2015 Apr 27.

Published in final edited form as: Pharmacotherapy. 2010 Dec;30(12):1279–1291. doi: 10.1592/phco.30.12.1279

Table 2.

Potential Mechanisms of Resistance

Regulatory System	Gene	Contributing Factors	Mechanism or Site of Action	Effect
PmrA-PmrB^34–43	PmrE	PhoP-PhoQ activation	Reduces negative charge of the bacteria’s lipid A and lipopolysaccharides	Reduced binding affinity
	PmrHFIJKLM	Mildly acidic pH
		High iron concentrations
		Low magnesium concentrations
PhoP-PhoQ^{33, 35–37, 44–48}	OprH	Exogenous polyamines	OprH proteins occupy membrane magnesium sites and reduce the binding site for colistin	Reduced binding affinity
		Low magnesium concentrations		Reduced binding affinity
Alterations in cell morphology⁴⁹	Unknown	Unknown	Spherical (vs rod shaped), reduced number and length of pili, increased topographic variability, finer surface texture	Increased rate of resistance