Architectural adaptation and protein expression patterns of Salmonella enterica serovar Enteritidis biofilms under laminar flow conditions

Salmonella enterica serovar Enteritidis is a significant biofilm-forming pathogen. The influence of a 10-fold difference in nutrient laminar flow velocity on the dynamics of Salmonella Enteritidis biofilm formation and protein expression profiles were compared in order to ascertain how flow velocity influenced biofilm structure and function. Low-flow (0.007 cm s− 1) biofilms consisted of diffusely-arranged microcolonies which grew until merging by ∼ 72 h. High-flow (0.07 cm s− 1) biofilms were significantly thicker (36 ± 3 µm (arithmetic mean ± standard error; n = 225) versus 16 ± 2 µm for low-flow biofilms at 120 h) and consisted of large bacterial mounds interspersed by water channels. Lectin-binding analysis of biofilm exopolymers revealed a significantly higher (P < 0.05) proportion of N-acetylgalactosamine (GalNAc) in low-flow biofilms (55.2%), relative to only 1.2% in high-flow biofilms. Alternatively, the proportions of α-l-fucose and N-acetylglucosamine (GlcNAc2)-N-acetylneuraminic acid (NeuNAc) polymer-conjugates were significantly higher (P < 0.05) in high-flow biofilms (69.1% and 29.6%, respectively) than low-flow biofilms (33.1% and 11.7%, respectively). Despite an apparent flow rate-based physiologic effect on biofilm structure and exopolymer composition, no major shift in whole-cell protein expression patterns was seen between 168 h-old low-flow and high-flow biofilms, and notably did not include any response involving the stress response proteins, DnaK, SodB, and Tpx. Proteins involved in degradation and energy metabolism (PduA, GapA, GpmA, Pgk, and RpiA), RNA and protein biosynthesis (Tsf, TufA, and RpoZ), cell processes (Crr, MalE, and PtsH), and adaptation (GrcA), and some hypothetical proteins (YcbL and YnaF) became up-regulated in both biofilm systems relative to a 168 h-old planktonic cell control. Our results indicate that Salmonella Enteritidis biofilms altered their structure and extracellular glycoconjugate composition in response to flow and this response is suggested to be significant in the survival of this pathogen as biofilms.