Persistent in vitro survival of coagulase-negative staphylococci adherent to intravascular catheters in the absence of conventional nutrients

Abstract

The in vitro survival of coagulase-negative staphylococci in media devoid of routine nutritional supplementation was assessed in the presence and absence of catheter materials to evaluate bacterium-device interactions. Strains of slime- and non-slime-producing coagulase-negative staphylococci were suspended in phosphate-buffered saline together with multiple segments of polyvinyl chloride (PVC), Teflon, Silastic, and polyurethane catheters and in control suspensions without catheters. Catheters were removed at 2 min and 24, 48, 72, and 96 h of incubation and washed thoroughly, and semiquantitative roll cultures were performed on blood agar. In addition, after 96 h catheters were introduced into tryptic soy broth (TSB), and roll cultures were performed after 18 h of incubation. Results demonstrated that after 96 h, 6 of 32 catheter specimens (4 PVC) had greater than 10 CFU of coagulase-negative staphylococci per catheter; after TSB addition, 18 of 32 catheter specimens had greater than or equal to 100 CFU per catheter (8 of 8 PVC catheters had greater than 1,000 CFU per catheter). In control suspensions, no growth was seen at 96 h or after TSB addition. No differences in the survival of slime- versus non-slime-producing strains were observed in control or catheter studies. These findings suggest that both slime- and non-slime-producing coagulase-negative staphylococci survive in vitro on catheters (especially PVC) in the absence of conventional nutrients and can proliferate on catheters when nutrients are added. Catheter-adherent coagulase-negative staphylococci appear to possess survival mechanisms under adverse conditions which may relate to the genesis of occult foreign-body-associated infections.