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

A study of coronary dominance and its clinical significance

Background: Coronary artery disease (CAD) is the most common cause of morbidity and mortality especially in the developing countries. The aim of the study was to find out cardiac dominance percentages and its association with coronary artery stenosis among each pattern of dominance. The objectives were to assess coronary vessel morphology of patients within each pattern of dominance, to find if gender differences exist among dominance patterns and also to find the distribution percentages of stenosis among dominance patterns. Materials and methods: Four thousand angiograms from patients of Indian origin were studied prospectively after procuring the sanction for the same from the ethical committee of the pre-selected hospitals from four states of South India. Informed consents were obtained. Post CABG, post PCI patients and patient being diabetic for ≥5 years were excluded from the study. Results: Right cardiac dominance was seen in 85.5%, left in 9.7%, and co-dominant in 4.8% cases. The percentages of dominance were almost similar among both genders except for left dominance which were higher among male samples. The diameter of right coronary artery (RCA-p) and left circumflex coronary artery (LCx-p) coronary arteries were significantly associated with dominance patterns (DP). The prevalence of stenosis was more for left DP, followed by right DP and least for co-dominant patterns. Conclusions: There is a necessity to see association between dominance patterns with the CAD which can help the interventional cardiologists. The disease patterns in the present study were predominantly in the left dominant or in the co-dominant hearts