Effect of ampicillin on adhesive properties of bacteria examined by atomic force microscopy

Discovery of new antibacterial agents requires the development of novel techniques for bacteria surface characterization after treatment with antibiotics. In this study, we investigate the effect of ampicillin at MICs levels on adhesive properties of Gram-positive and Gram-negative bacteria, using atomic force microscopy (AFM). Our results revealed that the treatment leads to changes of bacterial surface properties, especially cell surface roughness. A nanomechanical alteration of the cells led to an increase of adhesive forces and rupture lengths. Changes in adhesive properties are determined not only by the modification of physicochemical cell properties but also by an increase in roughness, leading to an increase of the contact area with a cantilever tip. We discovered that the contribution of non-specific physicochemical interactions in the bacteria attachment to a substrate is not negligible and was significantly influenced by the presence of antibiotic. Ampicillin caused much greater change in the adhesion properties of Bacillus subtilis than Escherichia coli due to the mode of action of β-lactam antibiotic. Adhesion measurements may by a new way to investigate subtle changes of the bacterial surface properties caused by antibiotic, especially those targeting the bacterial cell wall. In contrast to nanoindentation assays, they provide information on adhesive properties of the bacteria surface.