A physical chemical study of cells of strains of Pseudomonas aeruginosa
Electrokinetic studies were used to investigate differences in surface components associated with cells of Pseudomonas aeruginosa which were sensitive, naturally resistant or had an induced in vitro ("trained") resistance to the antibiotic gentamicin. The standard method of electrophoretic mobility measurement was modified for measurements at 10°C, at which temperature mobility values were not influenced by cell motility. The pH-mobility curves of cells grown at 37°C on solid medium revealed that cells of resistant strains could be distinguished from cells of sensitive strains. The surfaces of all cells probably carry charged carboxyl and amino groups and the differences between the surfaces of sensitive and resistant cells are due, in part, to differing ratios of these two components. In addition, cells with medium-level and high-level natural resistance to gentamicin are distinguished by their pH-mobility curves after treatment with l-fluoro-2,4-dinitrobenzene. Cells with induced resistance form a third, distinct, category of resistant cells for which the surface properties revert back to those of the parent, sensitive, cells after initial disturbance at the onset of "training"; this induced resistance is unstable. Although cells of all strains contain the same proportions of total solvent-extractable lipid, this was composed of different types of lipid and was distributedin different ways. There was little, if any, detectable surface lipid on cells of sensitive strains, while cells of naturally resistant and induced resistant strains possessed significant amounts of neutral lipid at the surface; there was an apparent relationship between the level of resistance and the amount of surface lipid possessed by the cells.