SUMMARY: The electrophoretic mobility (EPM) of a variety of Gram-negative and Gram-positive bacteria was measured with a Penkem S3000 analyser. Under standard growth conditions and neutral pH all cells displayed a negative EPM. The polysaccharide capsules of strains Kl, K5, K29 and K30 generated the highest EPM; to a lesser and varying degree O-antigens with charged groups and core lipopolysaccharides also contribute to the net EPM. Very little negative EPM was measured in suspension cultures of the gliding bacterium U67. No difference in the EPM was observed between rapidly growing and stationary-phase B. De-energization of the cell membranes by carbonyl cyanide m-chlorophenylhydrazone (CCCP) did not affect the EPM of wild-type and deep rough mutants of ; and the EPM of U67 and remained unaltered by CCCP when measured in their respective growth media. Extrusion of filamentous bacteriophage f1 from cells of its host, A95, caused a shift to a higher negative EPM. We also measured a variety of Grampositive strains, all of which displayed different EPMs. When membrane fractions of were adsorbed to latex spheres, characteristic differences between the EPM of beads coated with either inner or outer membrane were observed. The results suggest that the rapid EPM analysis is a useful tool to study the net electric charge of microorganisms and to examine changes of surface properties during interaction of cells with viruses, proteins (antibody) and charged antibiotics.


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