When bacteria find the proper environmental conditions they will form irreversible attachments on the surface, attracting more bacteria, increasing their local concentration. When a certain threshold of bacteria is reached they will start to shield themselves with an exopolysaccharide (EPS) matrix forming a biofilm. Bacteria inside biofilm are known to be up to 1000 times more resistant to different antibiotics. It is essential to prevent bacterial initial attachment and further biofilm formation.
In this study, Surface Plasmon Resonance imaging (SPRi) was used to real-time monitor the effect of different flow rates on attachment and growth of Staphylococcus aureus. SPRi sensor is capable of label-free detection over 1cm2 field of view. This sensor is connected to a fluidic system allowing the control of nutrient flow rates throughout the entire experiment. Increasing the flow rate will induce the shear stress on the surface and will prevent the initial attachment of bacteria. One the other hand, higher flow rate provides more fresh food for bacteria to grow over time.
Using SPRi the effect of flow rate on S. aureus growth was studied over 24 hours. 15μl of S. aureus bacteria media were loaded on the sensor surface and fresh Lysogeny Broth (LB) media was continuously flowed over the surface at 10μl/min (slow flow rate) and 120 μl/min (fast flow rate). The internal CCD camera provides difference images of the sensor surface every three seconds which allows real-time monitoring of the entire surface as bacteria adhere and grow on it. The results obtained from comparing these images showed higher bacterial growth under lower flow rate. As a validation to visually compare bacterial growth, after each experiment the sensor surface was removed from the instrument and the surface was stained with crystal violet which stains the live bacteria. The staining results showed higher bacterial growth under lower flowrate which were consistent with the results from SPRi study.