Membrane-targeted synergistic activity of docosahexaenoic acid and lysozyme against Pseudomonas aeruginosa

Abstract

SYNOPSIS Antimicrobial polypeptides including lysozymes (Ly) have membrane perturbing activity and are well documented effector molecules of innate immunity. In cystic fibrosis, a hereditary disease with frequent lung infection with Pseudomonas aeruginosa, the free fatty acid docosahexaenoic acid (DA), but not oleic acid (OA), is decreased and DA supplementation has been shown to improve the clinical condition in these patients. We hypothesized that DA may alone, or in conjunction with Ly, exert antibacterial action against P. aeruginosa. We found that DA and Ly synergistically inhibit the metabolic activity of P. aeruginosa, in contrast to OA. Electron microscopy and equilibrium dialysis suggest that DA accumulates in the bacterial membrane in the presence of Ly. Surface plasmon resonance with live bacteria and differential scanning calorimetry studies with bacterial model membranes reveal that, initially, DA facilitates lysozyme incorporation into the membrane, which in turn allows influx of more DA leading to bacterial cell death. Our study elucidates a molecular basis for the synergistic action of free fatty acids and antimicrobial polypeptides, which may be dysfunctional in cystic fibrosis.

Antimicrobial Role of Human Meibomian Lipids at the Ocular Surface

“…Indeed, synergistic interactions between antimicrobial lipids and proteins for intrinsic host defense have been demonstrated in some reports. 18,26,36 A review of the normal ocular microbiota shows that numbers of microorganisms that can be isolated from tears (<100 CFU/lL) are strikingly less than those isolated from saliva (10 7 -10 8 CFU/lL). 37 Although these secretions have similar antimicrobial proteins for innate defense, the apparent difference in the microbial load may be attributed to the lipid quantities that the two secretions contain.…”

Nutrient Signaling: Evolutionary Origins of the Immune-Modulating Effects of Dietary Fat

“…In the human colon, the concentration of shorter-chain FA have been measured in the millimolar range (e.g., 124 mM ;Bergman 1990) and that has been shown to inhibit the growth of bacteria such as E. coli O157:H7 . Although the effects of inhibitory FA and monoglycerides on bacterial growth are additive (Sun et al 2003), many FA have synergistic effects against pathogens with other elements of the innate immune system, including antimicrobial peptides (Nakatsuji et al 2010), lactoferrin and lysozyme (Ellison and Giehl 1991;Martinez et al 2009), andgastric acid (Bergsson et al 2002;Thormar et al 2006). The amplification of antipathogen activity by host factors suggests that some FA, even at concentrations in which they are inactive in isolation, may have the ability to modify the gut microbiota in vivo and thus alter infectious risk.…”

Antimicrobial lipids: Emerging effector molecules of innate host defense

“…Tollin et al [38] reported synergistic activity between vernix caseosa lipids and the antimicrobial peptide LL37 whereby this effect was attributed to FFA in vernix. We found synergistic effects between nasal fluid lipid extracts and the antimicrobial peptide human neutrophil peptide HNP1 [53] , and between the free fatty acid docosahexaenoic acid and lysozyme [67] . The latter study demonstrated that in the presence of lysozyme, docosahexaenoic acid accumulates in the bacterial cell membrane.…”