Introduction
Infections associated with inserted or indwelling biomedical devices are often caused by Staphylococcus epidermidis and other coagulase-negative staphylococci, capable of biofilm formation. However, in numerous animal studies we have observed that Staphylococcus epidermidis resides in the peri-implant tissue rather than on the biomaterial implant itself.
Aim
To determine whether in humans tissue surrounding implants may be a reservoir for bacteria with the capacity to cause biomaterial-associated infection.
Method
Intravenous and intra-arterial catheters and surrounding tissues were excised from deceased ICU patients. Appropriate controls and blood samples were obtained. Catheter segments were sonicated and surrounding tissue was homogenized. Sonicate and homogenate were quantitatively cultured. Bacterial isolates were identified and S. epidermidis isolates were analysed for biofilm/virulence-associated genes by PCR.
Results
Thirty-five catheters from 18 patients were collected. Eight out of 35 (23%) peri-catheter tissues were highly culture positive (>100 colonies/biopsy), mainly for coagulase-negative staphylococci and enterococci. Corresponding catheter segments were culture-negative or only slightly culture positive. Six pairs of S. epidermidis strains from catheter segments and corresponding surrounding tissue were all positive for the biofilm/virulence genes agrC, aap, sarA, icaABC, atlE, and insertion sequence IS256.
Conclusion
Tissue around catheters in humans is an as yet unrecognized niche for bacteria such as S. epidermidis which have the capacity to cause biomaterial-associated infection.