Detecting Bacterial Surface Organelles on Single Cells Using Optical Tweezers

Bacterial cells display a diverse array of surface organelles that are important for a range of processes such as Bald intercellular communication, motility and adhesion leading to biofilm formation, infections, and bacterial spread. More specifically, attachment to host cells by Gram-negative bacteria are mediated by adhesion pill, which are nanometers wide and micrometers long fibrous organelles. Since these pill are significantly thinner than the wavelength of visible light, they cannot be detected using standard light microscopy techniques. At present, there is' no fast and simple method available to investigate if a single cell expresses pill while keeping the cell alive for further studies. In this study, we present a method to determine the presence of pili on a single bacterium. The protocol involves imaging the bacterium to measure its size, followed by predicting the fluid drag based on its size using an analytical Model, and thereafter oscillating the sample while a single bacterium is trapped by an optical tweezer to measure its effective fluid drag. Comparison between the predicted and the measured fluid drag thereby indicate the presence Herein, we verify the method using polymer coated silica microspheres and Escherichia coli bacteria expressing adhesion pili: Our protocol can in real time and within seconds assist single cell studies by distinguishing between piliated and nonpiliated bacteria.