(67e) Adhesion Kinetics of Staphylococcus Aureus during the First Stages of Biofilm Evolution

The ability of most bacteria to grow within structured microbial communities called biofilms is one of the major causes of antimicrobial resistance against antibiotics. Biofilms can withstand antibiotic dosages of up to 1000 times higher than they could resist as planktonic cells and are also associated with biofouling, where microorganisms attach to surfaces and reduce the performance of machines. These aggregates of bacteria are mostly found in wet environments and develop under hydrodynamic stress.

Bacterial adhesion on surfaces is the first step in the biofilm formation process. Thus, it is vital to understand the effect of hydrodynamic forces on the kinetics of bacterial adhesion. This study uses the BioFlux 200 system to investigate bacterial adhesion under fluid flow. Staphylococcus aureus planktonic cultures are first grown overnight in TSB broth without dextrose and then diluted in PBS to impede further bacterial growth. Cell adhesion assays are then performed under hydrodynamic stress at 37°C using 48-microwell Low Shear plates (maximum shear stress up to 20 dyn/cm²) with flow channel dimensions of 75µm depth and 350µm width. The system is connected to an inverted microscope, and images are generated at 5-minute intervals.

Data from the study indicates initial rate of cell adhesion decreases with increasing surface shear stress over the range of shear investigated. At shear stress of 1dyn/cm² the average initial rate of cell adhesion observed is nearly 42 cells/min whereas at shear stress of 4dyn/cm² the initial rate is halved to 21 cell/min. Further analysis also showed that as shear stress increased, the maximum number of cells that could adhere to the surface decreased significantly. For example, a 2.8-fold reduction in maximum number of cells attached per unit area was observed when the surface shear stress was increased from 1dyn/cm² to 4dyn/cm² within the flow channel. These findings can help us develop a working kinetic model for bacterial adhesion in the early biofilm evolution stages.

The success of this project may lead to improved understanding and control of bacterial adhesion and biofilm evolution. This may ultimately lead to novel diagnoses and treatment methods for global challenges caused by biofilms.

Funder Acknowledgment(s): This study was supported by an NSF CMMI Award # 2000330 to Dr. Patrick Ymele-Leki.