Morphology of bacterial attachment to cardiac pacemaker leads and power packs

The mode of growth of the bacteria adherent to the surfaces of various components of cardiac pacemakers infected with coagulase-negative staphylococci was examined by scanning and transmission electron microscopy. Within developing adherent microcolonies, coccoid cells could be clearly seen to be enveloped by an amorphous material that condensed radically upon dehydration for electron microscopy, producing an amorphous residue in scanning electron micrographs and a fibrous anionic ruthenium red-staining residue in transmission electron micrographs. The differences in morphologies of the condensed residues may reflect differences in exopolysaccharides elaborated by the microorganisms and the degree to which materials of host origin are incorporated. The coccoid cells of coagulase-negative staphylococci were less clearly seen in thick, mature, adherent biofilms on heavily colonized surfaces because the condensed residue of their exopolysaccharide glycocalyces covered, and sometimes occluded, the bacteria cells. These coagulase-negative staphylococcal strains appeared to produce more exopolysaccharide material than did the strains infecting various intravascular catheters.