Uremic patients are at high risk of acquiring a biofilm related illness as it usually takes some time to reach stage 5 of CKD and in the course of treatment several medical devices could be used. Intravascular or urinary catheters represent the most frequent cause of medical device related pathologies, but it is during the phase of chronic kidney replacement therapy that uremic patients are at higher risk. During chronic hemodialysis infections, with related inflammatory events activation, may take place not only from vascular access but also from dialysis apparatus . Even in the absence of standardized collection methods, biofilm has been detected in the hydraulic circuits of hemodialysis machines particularly in low-flux sections, loops and ultrafilters. In this biofilm, the concentrations of bacteria and endotoxins can range from 1.0 X 103 to 1.0 X 106 cells/cm2 and 1-10EU/cm2, respectively. Several constituents of cell wall of viable or not viable microorganisms can be released into the dialysate, including high molecular weight substances (>100,000 Da) as well as low molecular weight ones (<1,000 Da) or DNA fragments . These molecules can stimulate circulating and membrane adherent leukocytes to release pro-inflammatory cytokines (IL-1p, TNF-a), important co-causal factors of the chronic micro-inflammatory condition of the hemodialysis patients. This specific chronic induction of pro-inflammatory cytokines could contribute to the MIA syndrome or to EPO resistance in dialysis patients .
Dialysis monitors are at risk of microbiological contamination from different entrances. Feeding water from water treatment system, concentrate salts and drain backflow are well-documented causes while critical is the water pipe connecting distribution loop with individual hemodialysis monitor where biofilm may take place during water stagnant phases (e.g., during the night).
Of note, microbiological controls (either bacteria or endotoxins), performed on water for dialysis or dialysate according to even most recent standards , evaluate contamination from planktonic bacteria but not from sessile microorganisms and only testing the levels of cytokines inducing substances are related to biofilm and to hazards for patient health .
Therefore to prevent biofilm, in the absence of assurances for a satisfactory microbial level, proper disinfection protocols for the complete water distribution system, including connecting pipes and dialysis monitors, must be instituted in each dialysis unit (figs. 1-7).
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