Self-repair Of Bacterial Cell Wall Against Multiple Puncturings By An AFM Tip

Abstract

We report, for the first time, that bacteria survive multiple stabbings by an atomic force microscopy (AFM) tip under physiological conditions. Experiments were conducted using Salmonella Typhimurium as a model. The fimbriae (pili) of S. Typhimurium and the corresponding antibody were used to immobilize live bacteria in well-defined patterns on a flat substrate. A carefully calibrated AFM was used to conduct the experiments in a growth medium: An AFM tip with known radius was used to apply pressure to a bacterium with a known force until the tip penetrated the bacterium cell wall and reached the other side of the bacterium. This experiment, which generated a characteristic puncture curve, was repeated more than 50 times at different locations on the same bacterium. A MatLab® code was written to analyze the puncture curves, which carry an abundance of information on such characteristics of the bacterium as the surface elasticity, the critical pressure needed to puncture the bacterial cell wall, the interaction of the AFM tip with the interior of the bacterium and the precise width of the bacterium in the physiological environment. The results were compared with similar results obtained from dead bacteria. High-resolution optical microscopy was employed to monitor the viability of the bacteria under study before and after the stabbings. The evidence suggests that bacteria are still alive after multiple puncturings! The results are tentatively explained in terms of self-repair of the lipid bilayers and of the peptidoglycan layer of S. Typhimurium against multiple puncturing events exerted by an AFM tip.