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Abstract Background Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events. Methods Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD). Results Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa. Conclusions This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.

Aortic stiffness, a predictive parameter in cardiovascular medicine, is blood pressure dependent and experimentally requires isobaric measurement for meaningful comparison. Vasoactive drug administration to change peripheral resistance and blood pressure allows such isobaric comparison but may alter large conduit artery wall tension, directly changing aortic stiffness. This study quantifies affects of sodium nitroprusside (SNP, vasodilator) and phenylephrine (PE, vasoconstrictor) on aortic stiffness measured by pulse wave velocity (aPWV) assessed by invasive pressure catheterization in anaesthetized Sprague-Dawley rats (n=7). This was compared to non-drug dependent alteration of blood pressure through reduced venous return induced by partial vena-cava occlusion. In-vivo drug concentration was estimated by modeling clearance rates. Ex-vivo responses of excised thoracic and abdominal aortic rings to drugs was measured using myography. SNP administration did not alter aPWV compared to venous occlusion (p=0.21-0.87). There was a 5% difference in aPWV with PE administration compared to venous occlusion (p<0.05). The estimated in-vivo maximum concentration of PE (7.0±1.8 ×10-7 M) and SNP (4.2±0.6 ×10-7 M) caused ex-vivo equivalent contraction of 52 mmHg (thoracic) and 112 mmHg (abdominal) and relaxation of 96% (both abdominal and thoracic) respectively, despite having negligible effect on aPWV in-vivo. This study demonstrates that vasoactive drugs administered to alter systemic blood pressure have negligible effect on aPWV and provide a useful tool to study pressure normalized and pressure dependent aPWV in large conduit arteries in-vivo. However, similar drug concentration affects aortic ring wall tension ex-vivo. Future studies investigating in-vivo and ex-vivo kinetics will elucidate mechanisms for this marked difference. [ABSTRACT FROM AUTHOR]

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events.Methods: Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD).Results: Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa.Conclusions: This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis. [ABSTRACT FROM AUTHOR]