The ultrastructure of antibiotic-susceptible and multi-resistant strains of group JK diphtheroid rods isolated from clinical specimens.

Two antibiotic-susceptible and two multi-resistant strains of diphtheroid rods of the group JK, obtained from clinical specimens in Denmark and from CDC in the U.S. were studied. The cells of all four strains presented an ordinary Gram-positive cell wall and an additional surface layer. Septum formation in dividing cells appeared to result in a "snapping-like" dividing mechanism, thus corroborating the relationship of the JK cells to the genus Corynebacterium. A significantly increased thickness of the surface layer of the multi-resistant strains was observed when cells were treated with ruthenium red. It is suggested that such a structural difference on the exterior of the cell-wall among JK bacteria may affect the cell-wall's permeability to antibiotics.