The pathogenesis and epidemiology of catheter-related infection with pulmonary artery Swan-Ganz catheters: a prospective study utilizing molecular subtyping

Decreased bacterial adherence and biofilm formation on chlorhexidine and silver sulfadiazine-impregnated central venous catheters implanted in swine

OBJECTIVE

To determine if antiseptic central venous catheters impregnated with silver sulfadiazine and chlorhexidine (antiseptic) reduce bacterial adherence and biofilm formation without producing local or systemic toxicity.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Ten outbred New Hampshire pigs.

INTERVENTIONS

Nonimpregnated (control) and antiseptic-impregnated catheters were inserted intravascularly into swine for 7 days. After explantation, the catheters were assessed for bacterial adherence and biofilm formation, and the surrounding tissue was assessed for signs of toxicity. Before retrieval, systemic concentrations of antimicrobials were determined.

MEASUREMENTS AND MAIN RESULTS

Sequential roll plate and centrifuging were used to detect moderately and tightly adherent bacteria on the outer and luminal surfaces of the catheter. The presence of biofilm was detected by scanning electron microscopy. Tissues surrounding the catheters were examined histopathologically; systemic concentrations of chlorhexidine, sulfadiazine, and silver were determined by atomic absorption and high-performance liquid chromatography. As compared with the controls, antiseptic catheters had significantly (p < .01) fewer moderately and tightly adherent bacteria on outer and luminal surfaces, and fewer adherent bacteria when outer surfaces alone were examined (p < .01). Scanning electron microscopy showed bacterial biofilm and adherence on the control catheters but not on the antiseptic catheters. There were no abnormal histopathologic changes associated with the test catheter, and serum concentrations of the antibacterial agents were shown to be within nontoxic ranges.

CONCLUSION

The antiseptic-impregnated catheters prevented bacterial adherence and biofilm formation and produced no local or systemic toxicity.

Pathogenesis of infections related to intravascular catheterization

Over the past few decades, there have been major technological improvements in the manufacture of intravenous solutions and the manufacture and design of catheter materials. However, the risk of infection in patients receiving infusion therapy remains substantial, in part because of host factors (for example, increased use of immunosuppressive therapy, more aggressive surgery and life support, and improved survival at the extremes of life) and in part because of the availability of catheters that can be left in place for very long periods. Microbial components of normal skin flora, particularly coagulase-negative staphylococci, have emerged as the predominant pathogens in catheter-associated infections. Therefore, efforts to prevent skin microorganisms from entering the catheter wound (such as tunnelling of catheters and use of catheter cuffs and local antimicrobial agents) are logical and relatively effective. The specific properties of microorganisms that transform normally harmless commensals such as coagulase-negative staphylococci into formidable pathogens in the presence of a plastic foreign body are being explored. For example, Staphylococcus epidermidis elaborates a polysaccharide adhesin that also functions as a capsule and is a target for opsonic killing. However, the interactions between microorganism and catheter that lead to adherence, persistence, infection, and dissemination appear to be multifactorial.

Isolation and characterization of transposon mutants of Staphylococcus epidermidis deficient in capsular polysaccharide/adhesin and slime

We used transposon (Tn) mutagenesis to study the role of capsular polysaccharide/adhesin (PS/A) and slime in adherence of Staphylococcus epidermidis to catheters. pLTV1, containing Tn917-LTV1, was transformed into S. epidermidis M187 by protoplast fusion with S. aureus RN4220(pLTV1), creating M187(pLTV1). Tn mutants were isolated following growth at 42 degrees C; mutants deficient in PS/A and slime production were selected. PS/A- and slime-deficient Tn mutants had a 10-fold decrease in vitro in the initial phase of adherence to catheters, comparable to levels of strains that do not produce PS/A. Introduction of Tn917-LTV1-interrupted DNA from PS/A-deficient mutant M187sn3 into the parental strain via transformation of protoplasts yielded recipients with inserts identical to those of the Tn mutant that were PS/A and slime deficient. Chromosomal DNA flanking the Tn in mutant M187sn3 was cloned into Escherichia coli. The cloned DNA was found to hybridize to approximately 5-kb EcoRI fragments from the parental strain and from control Tn mutants that express parental levels of PS/A and to either approximately 9- or approximately 14-kb EcoRI fragments from other highly adherent, PS/A-producing strains. Mapping studies demonstrated that in the eight PS/A-deficient mutants that have been isolated, the Tn insertions all occur within a region of approximately 11.6 kb that is defined by three EcoRI sites. These results support previous findings indicating that in S. epidermidis PS/A is involved with in vitro adherence to plastic biomaterials and elaboration of PS/A is closely associated with slime production.