Oscillatory surface rheotaxis of swimming E. coli bacteria

Bacterial contamination of biological conducts, catheters or water resources is a major threat to public health and can be amplified by the ability of bacteria to swim upstream. The mechanisms of this rheotaxis, the reorientation with respect to flow gradients, often in complex and confined environments, are still poorly understood. Here, we follow individual E. coli bacteria swimming at surfaces under shear flow with two complementary experimental assays, based on 3D Lagrangian tracking and fluorescent flagellar labelling and we develop a theoretical model for their rheotactic motion. Three transitions are identified with increasing shear rate: Above a first critical shear rate, bacteria shift to swimming upstream. After a second threshold, we report the discovery of an oscillatory rheotaxis. Beyond a third transition, we further observe coexistence of rheotaxis along the positive and negative vorticity directions. A full theoretical analysis explains these regimes and predicts the corresponding critical shear rates. The predicted transitions as well as the oscillation dynamics are in good agreement with experimental observations. Our results shed new light on bacterial transport and reveal new strategies for contamination prevention.Comment: 12 pages, 5 figure

Preventive effects of protopanaxadiol and protopanaxatriol ginsenosides on liver inflammation and apoptosis in hyperlipidemic apoE KO mice

Ginsenosides, bioactive compounds of Panax GinsengC.A. Meyer, are divided into protopanaxadiol (PD) and protopanaxtriol (PT). The aim of this study was to evaluate the protective effects of different PD and PT combination ratios on liver inflammation and apoptosis in hyperlipidemic apo E KO mice. R1 (PD/PT = 1, high Rg1 and Rb1) and R2 (PD/PT = 2, high Re and Rd) extracts were intraperitoneally injected by 100 mg/kg/day at the 8th week. R1 and R2 improved atherogenic indices by increasing HDL and lowering total cholesterol (TC) and triacylglyceride (TG) selectively. R1 decreased lipid peroxides (LPO) level in plasma and liver tissue of hyperlipidemic mice, and R2 lowered plasma malondialdehyde(MDA) level. R1 and R2 not only regulated the expression of cyclooxygenase (COX)-2, IκB-α, phopho-ERK 1/2, and phopho-SAPK/JNK levels but also were significantly effective in blocking apoptotic signals, such as caspase-8, -9, as well as the cleavage of PARP in liver. Different combinational treatment of PD and PT extracts might ameliorate the liver inflammation and apoptosis in hyperlipidemic apo E KO mice, which is atherosclerotic animal model