Exogenous α-linolenic acid acts as a negative regulator of Cronobacter sakazakii structural flagellar proteins.

Aim: This work aims to report on the mechanism of action by which Cronobacter sakazakii virulence is impacted by α-linolenic acid (ALA), a C18:3 fatty acid.

Methods and results: To elucidate this, two concentrations of ALA (250 and 1000 µmol L-1) were added exogenously to C. sakazakii 29 544 in tryptic soy broth. Quantitative proteomic analysis using label-free mass spectrometry showed significantly different proteomic profiles of treated and control C. sakazakii samples. Across both ALA treatments, a total of 11 flagellar proteins were identified as reduced in abundance and showed a dose-dependent response. Gene expression studies revealed ALA acts as a negative regulator of fliD, flgL and fliE. The TTC motility medium assay and the soft agar assay were performed to determine the effect of ALA on bacterial motility and results showed reduced motility of C. sakazakii (P = 0.01, 0.001). Other proteins with altered abundance include the methyl-accepting chemotaxis protein, the iron donor protein IscX and the cellulose biosynthesis protein BcsR.

Conclusions: Antimicrobial lipids, such as fatty acids, are reported to act as regulatory molecules, capable of modulating virulence factors in Gram-negative pathogens such as Cholera and Salmonella species. Through proteomic analysis, RT-qPCR and functional assays, the results indicate that ALA negatively regulates flagellar genes, resulting in reduced expression of structural proteins and subsequent loss of motility.