Heterogeneity of surfaces of subgingival bacteria as detected by zeta potential measurements.

Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans (A.a.) are Gram-negative bacteria which are implicated in various forms of periodontal disease. The Gram-positive Peptostreptococcus micros may also play an important role. For investigation of the possible adhesion and colonization mechanisms of these organisms, the charge properties of the outermost layers of bacterial cell surfaces were studied through the measurement of zeta potentials at various pH values. Eleven fresh clinical isolates, representing the four species, and one laboratory strain, P. gingivalis W83, were examined. Eleven of the 12 strains displayed heterogeneity with respect to pH-dependent zeta potentials. Within single cultures of each of these strains, two distinct populations of cells were found, one which was more negatively charged than the other. For the Gram-negative strains, the more negatively charged subpopulation was in the majority, while the P. micros strains appeared to be composed mainly of a less-negatively-charged subpopulation. Vesicles prepared from two strains displayed the same pH dependence and heterogeneity of zeta potentials as the parent cells. An A.a. strain which was passaged several times in fluid medium had lost its fimbriae and became homogeneous with respect to charge.