Observation of changes in bacterial cell morphology using tapping mode atomic force microscopy

Atomic force microscopy (AFM) was used in tapping mode to probe morphologic al changes in surface-confined cells resulting from adhesion-modifying chem icals. Bacteria (Burkholderia cepacia G4 and Pseudomonas stutzeri KC) were exposed to Tween 20, heparin, disodium tetraborate, sodium pyrophosphate, l ow ionic strength water, lysozyme/ethylenediaminetetraacetic acid (EDTA), a nd 3-(4-morpholino)propanesulfonic acid sodium salt (MOPS) buffer las a con trol), and the surface topography of the cells was examined after exposure to each chemical. Cells were attached to glass slides for AFM imaging by a new method of cross-linking carboxyl groups on the bacterial surfaces with amine groups that had been coupled to glass slides. Topographic images, pha se images, traces of surface topography, and analyses of surface roughness were performed on all samples. We are not aware of any studies besides the present one in which phase imaging has been used on bacteria. Height traces illustrated the effect of different chemical treatments on the cells by sh owing whether the topography of the cell was altered by the different treat ments. The surface roughness was quantified in terms of the root-mean-squar e (RMS) average of the height deviations. All of the treatment chemicals ex cept disodium tetraborate caused higher RMS values to be measured for G4 an d KC. Disodium tetraborate flattened the cells and, therefore, resulted in slightly lower or equal RMS values as the control (MOPS buffer). RMS values were correlated with the qualitative shapes of the cells. Lysozyme/EDTA, s odium pyrophosphate, and disodium tetraborate produced the most damage to c ellular morphology, as observed by topographic images and surface traces, a nd decreased cellular viability. These data show that AFM operated in tappi ng mode can provide a useful method for investigating the consequences of b acterial exposure to surface-modifying chemicals.