Exogenous polyunsaturated fatty acids (PUFAs) influence permeability, antimicrobial peptide resistance, biofilm formation and membrane phospholipid structure in an A‐layer and non‐A‐layer strain of Aeromonas salmonicida

Abstract

Aeromonas salmonicida is a Gram‐negative bacterium that can infect a wide host range of fish populations, including salmonids and non‐salmonids as well as freshwater and marine life. Some strains of A. salmonicida cause the disease furunculosis, which can cause lethargy, intestinal inflammation, ulcers, haemorrhaging and death. The infection is spread through fish‐to‐fish contact, and the presence of infection can have devastating effects on cultivated fish populations. The purpose of this study was to explore the ability of non‐A‐layer and A‐layer A. salmonicida strains to incorporate polyunsaturated fatty acids (PUFAs) into their lipid profile and test the phenotypic effects thereof. Lipids were extracted from PUFA‐exposed cultures and analysed for lipid modification by thin‐layer chromatography and ultraperformance liquid chromatography‐mass spectrometry, showing A. salmonicida, regardless of A‐layer, capable of incorporating all seven of the PUFAs studied. Phenotypic effects were determined through the use of assays that tested for biofilm formation, membrane permeability and cyclic peptide susceptibility. Temperature‐dependent effects on biofilm formation were observed, and PUFA exposure showed significant (p < .001) increases in membrane permeability as tested by the uptake of the hydrophobic compounds crystal violet and ethidium bromide. Additionally, some PUFAs elicited modest protection and vulnerability against the membrane‐targeting cyclic peptides polymyxin B (PMB) and colistin. The diverse, strain‐specific responses to exogenous PUFAs may allude to evolved adaptive strategies that enhance survival, persistence and virulence of non‐pathogenic and pathogenic members of bacteria that oscillate between environmental and fish host niches.

A Comprehensive Review of Recent Research into the Effects of Antimicrobial Peptides on Biofilms—January 2020 to September 2023

“…Interestingly, Hofer et al showed that polyunsaturated fatty acids (PUFAs) could generate modest protection or vulnerability to polymyxin B and colistin in Aeromonas salmonicida. They concluded that diverse, strain-specific responses to exogenous PUFAs may be an adaptive survival strategy in bacteria that fluctuate between fish and environmental niches [48]. Finally, Bordetella pertussis polysaccharide (Bps) was shown to resist AMP (LL-37, polymyxin B, HNP-1, and HNP-2) killing, helping 'shield' non-pathogenic K12 E. coli and increase in vivo bacterial survival in the respiratory tract [49].…”

Phylogenetic investigation of Gammaproteobacteria proteins involved in exogenous long-chain fatty acid acquisition and assimilation

“…Gammaproteobacteria contains many pathogens, such as several Vibrio species ( cholerae , parahaemolyticus , vulnificus , and alginolyticus) , Allivibrio ficheri , Klebsiella pneumoniae , and Pseudomonas aeruginosa , and the model bacterial organism Escherichia coli [ [3] , [4] , [5] , [6] , [7] , [8] ]. Many members of this class, including all the aforementioned species, are able to incorporate exogenous fatty acids, including polyunsaturated fatty acids (PUFAs), into the phospholipids of their membranes [ [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] ]. Such assimilation results in phospholipid structural modifications, causing increased membrane permeability to hydrophobic compounds and altered resistance to certain antibiotics.…”