1. Comparing Adhesive Properties of Streptococcus gordonii in Constant and Pulsatile Flow
Jasmine Hawkins, Freshman, Bioengineering
Summer Undergraduate Research Program 2015
Mentors: Jamie Nunez, Olga Yakovenko, Dr. Wendy Thomas, Bioengineering
Shear-enhanced adhesion is a mechanism in which binding is enhanced at high flow rates. Some
species of bacteria within the genus Streptococcus demonstrate shear-enhanced adhesion under
high flow conditions, which are present throughout the human body. The purpose of our research
is to understand and compare the effect of constant and pulsatile flow on Streptococcus gordonii, a
strain of bacteria that causes infections by binding to human platelets. Our research focuses
primarily on bacterial endocarditis, a life-threatening infection of the interior of the heart. Rates of
incidence in a general population has been estimated between 2 and 6 cases per 100,000 person-
years. In our model system, we utilize a flow chamber to mimic pulsatile flow conditions in heart
valves, which oscillate between a low and high flow, with a maximum shear stress of 2-8 Pa. We
hypothesize that under pulsatile flow, S. gordonii will preferentially attach to platelets under low
flow, and will switch to a robust stationary mode when placed under high flow. We took videos to
determine the number of bacteria that bind to platelets under both constant and pulsatile flow, and
analyzed these to determine the conditions that enhance adhesion. In constant flow, our results
indicate that S. gordonii bind best at a low shear stress. The peak of bacteria binding in pulsatile
flow is nearly 10 fold that of constant flow. This suggests that the binding of S. gordonii to platelets
is enhancedby pulsatile flow. Bothconstant and pulsatile flow indicate similar trends in the number
binding as the shear stress increases to high values. By understanding the adhesive properties of
these strains, our research has the potential to provide significant insights into understanding
shear-enhanced adhesion. Furthermore, our research may contribute to the development of anti-
adhesive therapies to treat bacterial endocarditis.