Scanning electron microscopy of bacteria adherent to intravascular catheters

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Abstract
Scanning EM 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 (.gtoreq. 15 colonies/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 106 colony-forming units of coagulase-negative staphylococci/ml suspended in phosphate-buffered saline. Unused sterile polyvinylchloride catheters were also examined. Scanning EM of unused sterile polyvinylchloride catheters demonstrated multiple linear surface irregularities. Scanning EM 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 EM 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.