Abstract: The aim of this study was to evaluate the inhibitory effect of protocatechuic aldehyde (PA), a plant-derived compound, on the swimming motility, biofilm formation, adhesion and invasion to Caco-2 cells of Cronobacter sakazakii and to determine its effect on the transcription of nine virulence genes in C. sakazakii. The results indicated that the minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of PA against six C. sakazakii strains were 2 mg/mL, and the sub-inhibitory concentrations against C. sakazakii ATCC29544 were 1/200, 1/100 and 1/50 MIC. PA at SICs inhibited the swimming motility on soft agar plates and biofilm formation of ATCC29544. PA substantially reduced its adhesion and invasion to Caco-2 cells, and repressed the expression of nine virulence genes in this strain. These findings suggest that PA can inhibit the virulence factors of C. sakazakii, and it has the potential to be developed as an alternative or supplemental agent to prevent and control infections caused by C. sakazakii.

Key words: Cronobacter sakazakii, protocatechuic aldehyde, sub-inhibitory concentration, virulence factors, virulence genes