Scanning electron microscopy of bacteria adherent to intravascular catheters

Scanning electron microscopy was used to assess the morphological features of coagulase-negative staphylococci adherent to polyvinylchloride intravascular catheter specimens. Clinical specimens were obtained by using patient catheters from which coagulase-negative staphylococci (greater than or equal to 15 colonies per catheter) grew on semiquantitative blood agar roll cultures. In vitro specimens were prepared by a previously published technique in which sterile polyvinylchloride catheters were immersed in 10(6) CFU of coagulase-negative staphylococci per ml suspended in phosphate-buffered saline. Unused sterile polyvinylchloride catheters were also examined. Scanning electron microscopy of unused sterile polyvinylchloride catheters demonstrated multiple linear surface irregularities. Scanning electron microscopy of infected patient catheters showed a diffuse amorphous material covering the entire surface and the presence of bacteria which appeared anchored to that surface by several different means. These included a slime layer, "foot" processes, and lodgement in surface irregularities. Scanning electron microscopy of in vitro specimens demonstrated no background surface coating, but it did show attachment of cocci to the surface by the same mechanisms as described for clinical specimens. These observations of similar means of attachment in clinical and in vitro specimens suggest that intrinsic catheter surface properties, bacterial surface features, and perhaps coating with host substances may all play a role in bacterial attachment to intravascular catheters. More sophisticated analysis of these interactions may clarify mechanisms of pathogenesis.