Triclosan-Induced Modification of Unsaturated Fatty Acid Metabolism and Growth in Pseudomonas aeruginosa PAO1

Abstract

Triclosan is a broad-spectrum antimicrobial agent having low toxicity which facilitates its incorporation into numerous personal and health care products. Although triclosan acts against a wide range of gram-positive and gram-negative bacteria by affecting fatty acid biosynthesis, it is ineffective against the opportunistic pathogen Pseudomonas aeruginosa. Wild-type strain P. aeruginosa PAO1 was used as a model system to determine the effects of triclosan on fatty acid metabolism in resistant microorganisms. This was accomplished by cultivating P. aeruginosa PAO1 cultures in the presence of different concentrations of triclosan, monitoring growth rates turbidimetrically, and harvesting in stationary phase. Readily extractable lipids (RELs) were obtained from freeze-dried cells after washing and analyzed using gas chromatography coupled with mass spectrometry. Resultant data demonstrated that triclosan caused dose-dependent increases in the amounts of trans-C(16:1) and trans-C(18:1) fatty acids, with concomitant decreases in their respective cyclopropyl analogs. Triclosan did not affect the relative concentrations of saturated, cis unsaturated, or the overall ratios of combined C(16) to C(18) fatty acid species. The readily extractable lipid fractions contained triclosan proportional to triclosan concentrations in the growth media. The presence or absence of triclosan in either liquid or solid media did not affect the antimicrobial susceptibilities of P. aeruginosa PAO1 to a battery of unrelated antimicrobials. Triclosan decreased growth rate in a dose-dependent manner at soluble concentrations. Incorporation of triclosan into the REL fraction was accompanied by increased levels of trans unsaturated fatty acids, decreased levels of cyclopropyl fatty acids, and decrease in growth rate. These alterations may contribute to triclosan resistance in P. aeruginosa PAO1.

Effect of Triclosan and Chloroxylenol on Bacterial Membranes

“…In the published studies on triclosan, the membranes used consisted of saturated and unsaturated nonbranched-chain lipids, − but such lipids are characteristic of eukaryotic membranes. In most bacteria, most phospholipids contain large amounts of branched-chain fatty acids such as iso and anteiso methyl-branched fatty acids (as in S. aureus , Listeria , and Legionella ) and cyclopropane fatty acids (as in E. coli , Salmonella , and Mycobacterium ). − Branched-chain lipids change the physicochemical and structural properties of membranes, in particular their level of fluidity. , Although they have been associated with enhanced resistance or susceptibility to antimicrobial peptides , and, in the case of cyclopropane lipids, with the development of triclosan resistance, how branched-chain lipids affect the activity of widely used biocides remains uncertain.…”

“…30−32 Branchedchain lipids change the physicochemical and structural properties of membranes, in particular their level of fluidity. 33,34 Although they have been associated with enhanced resistance or susceptibility to antimicrobial peptides 35,36 and, in the case of cyclopropane lipids, with the development of triclosan resistance, 37 how branched-chain lipids affect the activity of widely used biocides remains uncertain.…”