Variations in the Morphology, Mechanics and Adhesion of Persister and Resister Cells in Response to Ampicillin: AFM Study.

Persister bacterial cells are great at surviving antibiotics. The phenotypic means by which they do that are underexplored. As such, atomic force microscope (AFM) was used to quantify the contributions of the surface properties of the outer membrane of multidrug resistance (MDR)- Strains (A5 and A9) in the presence of ampicillin at minimum inhibitory concentration (MIC) (resistant cells) and at 20× MIC (persistent cells). The properties quantified were morphology, root mean square (RMS) roughness, adhesion, elasticity, and bacterial surface biopolymers' thickness and grafting density. Compared to untreated cells, persister cells of A5 increased their RMS, adhesion, apparent grafting density, and elasticity by 1.2, 3.4, 2.0, and 3.3 folds, respectively, and decreased their surface area and brush thickness by 1.3 and 1.2 folds, respectively. Similarly, compared to untreated cells, persister cells of A9 increased their RMS, adhesion and elasticity by 1.6, 4.4, and 4.5 folds, respectively; decreased their surface area and brush thickness by 1.4 and 1.6 folds, respectively; and did not change their grafting densities. Our results indicate that resistant and persistent A5 cells battled ampicillin by decreasing their size and going through dormancy. The resistant A9 cells resisted ampicillin through elongation, increased surface area, and adhesion. In contrast, the persistent E. A9 cells resisted ampicillin through increased roughness, increased surface biopolymers' grafting densities, increased cellular elasticities, and decreased surface areas. Mechanistic insights into how the resistant and persistent cells respond to ampicillin's treatment are instrumental to guide design efforts exploring the development of new antibiotics or renovating the existing antibiotics that may kill persistent bacteria by combining more than one mechanism of action.