Incremental increases in physiological fluid shear progressively alter pathogenic phenotypes and gene expression in multidrug resistant Salmonella
The ability of bacteria to sense and respond to mechanical forces has important implications for pathogens during the in vivo infection process, as they experience wide fluid shear fluctuations in the host.  However, relatively little is known about how mechanical forces encountered in the infected host drive microbial pathogenesis.  We previously demonstrated an inverse relationship between fluid shear-induced responses of classic gastrointestinal disease-causing Salmonella Typhimurium (x3339) and systemic multidrug resistant (MDR) S. Typhimurium (ST313 D23580) when the organisms were cultured under fluid shear forces like those in the intestinal tract and bloodstream.  To advance our understanding of how incremental increases in physiological fluid shear impact D23580 pathogenesis phenotypes and transcriptomic responses, we applied dynamic bioreactor technology to introduce and quantify incremental increases in fluid shear during culture. Our data indicate that D23580 responds dynamically to a range of physiological fluid shear levels by altering pathogenesis-related phenotypes (stress responses, host cell colonization) and transcriptomic responses (including genes important for adherence and invasion).  These phenotypic and molecular genetic changes directly correlated with incrementally increased fluid shear. This is the first demonstration that incremental changes in fluid shear alter stress responses and gene expression in any ST313 strain and offers new insight into how physiological fluid shear forces encountered by MDR bacteria in the infected host might impact their disease-causing ability in unexpected ways. Overall design: RNA-Seq was performed on an Illumina HiSeq-2000 sequencer to profile the entire D23580 transcriptome. Three RNA sample types were processed: no bead (FS1), 1/8-PolyPropylene bead (FS3), and 1/8-Ceramic bead (FS4).  For all three RWV conditions (FS1, FS3 and FS4), the RNA samples were prepared from two sets of biological replicates of D23580 cultures grown in LB medium to stationary phase for 24 hours at 37 °C.