Biofilm and Disinfection in Dialysis

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Disinfection enters the quality assurance program in dialysis and represents part of the various anti-inflammatory treatment strategies adopted to improve outcome in these patients.

Several liquid chemical germicides or physical disinfectant techniques are commercially available and choice is based not only on effectiveness but also

Biofilm Ureteral Stent
Fig. 1. Subsequent phases of biofilm formation with bacterial deposition (a), attachment (b), growing (c) up to a mature biofilm (d) onto a silicone tube from a dialysis monitor hydraulic circuit.
Biofilm Dialysis Catheter
Fig. 2. Biofilm presence on a peritoneal dialysis catheter removed because of peritonitis caused by colonization.
Biofilm Dialysis Catheter
Fig. 3. Ureteral stent showing biofilm, cellular debris and erythrocytes at different magnifications.
Biofilm Biomass
Fig. 4. Biofilm on a urinary catheter with bacteria released from biomass.

on effects in term of tolerability on piping and accessories materials as reported in table 2.

Today, as a matter of fact, disinfectants in dialysis are considered as class II devices and therefore regulated by FDA in the US and CE mark application directives in Europe. Therefore disinfection is a part of the maintenance procedure validated by device manufacturers, and health care professionals need to comply with suggested and validated protocols [16].

Biofilm Ureteral Stent
Fig. 6. A filtration membrane from water treatment system with inorganic (crystals) and bacterial deposition.
Hypochlorite Sodium Biofilm
Fig. 7. Biofilm presence on a water treatment system showing PVC piping irregular surface and bacterial deposition (a). Mature biofilm with inorganic salts deposition found in a low flux zone of a dialysis monitor (b, c).
Table 2. Disinfectants used in dialysis for water treatment systems and monitors with compatibility for piping material

Water treatment system

Monitors

Compatibility

Chemical

Hypochlorites

X

X

PVC, PVDF, PEX, PP, PE

Peracetic acid

X

X

PVC, PVDF, PEX, PP, PE, ABS

Chlorine dioxide

X

PVC, PVDF, PEX, PP, PE

Formaldehyde

X

PVC, PVDF, PEX, PP, PE, SS

Ozone

X

PVC (low concentration), PVDF, SS

Physical

Ultraviolet irradiators

X

nr

Hot water (>80°C)

X

X

PVDF, PEX, SS

ABS = Acrylonitrile butadiene styrene; nr = not reported; PE = polyethylene; PEX = cross-linked polyethylene; PP = polypropylene; PVC = polyvinylchloride; PVDF = polyvinylidene fluoride; SS = stainless steel.

ABS = Acrylonitrile butadiene styrene; nr = not reported; PE = polyethylene; PEX = cross-linked polyethylene; PP = polypropylene; PVC = polyvinylchloride; PVDF = polyvinylidene fluoride; SS = stainless steel.

The importance of biofilm avoidance in dialysis disinfection procedures has been demonstrated as it causes a bacterial regrowing after some hours from a standard disinfection and it affects efficiency of both chemical or heat disinfections [17]. In search of optimal treatment for a combined action on microorganisms and biofilm several research papers describe effects from chemical disinfection alone or in conjunction with some physical treatment. Hypochlorite has offered a concentration dependent effect on biofilm removal, but only auto-claving is able to obtain a complete biofilm removal [18, 19].

When comparing some oxidizing, non-oxidizing and surfactant agents, chemicals, associated with mechanical treatment, have been reported to be weak agents in biofilm removal and some of them may cause even an increase in biofilm mechanical stability [20]. Ultraviolet treatment too, seems of little impact as it is unable to modify pathogen adhesion on biofilm within a water distribution system [21]. An effective procedure to remove biofilm from tubing surface of monitors previously disinfected with peroxyacetic and citric acid has been described with an enzyme/detergent combination leading to a complete detachment of the biomass [22]. In presence of biofilm the efficacy of both chemical and physical conventional disinfection procedures on hemodialysis monitors is significantly reduced for both CFU and endotoxins. Chemical disinfectants such as peracetic acid, hydrogen peroxide and hypochlorite used alone at concentrations of clinical practice cannot effectively remove the biofilm in experimental conditions. The penetration of a disinfectant into the biofilm appears to be the major rate-limiting factor and it is postulated that only the outermost layers of the biofilm is affected by disinfectant because diffusion into the biomass is impeded by the polysaccharide matrix. Hydrogen peroxide and citric acid for their detergent effect have a better microbial detachment efficacy, but a lower bactericidal activity compared with peracetic acid and hypochlorite. The combination of a chemical with detergent effect (such as citric acid) and a chemical with high disinfectant activity (such as hypochlorite) offers better results on reduction of CFU, but still results as incompletely efficient in cell detachment from tubing surfaces. As a result, the endotoxin concentration is not effectively reduced and residual biofilm allows re-growing and a new colonization.

Isolated heat disinfection at temperatures between 70 and 95°C, as in most hemodialysis apparatuses, cannot remove biofilm and produces a lower reduction of CFU when compared to chemical disinfectants such as hypochlorite and peracetic acid. When heat is combined with chemical detergent agents it has a better efficacy on CFU reduction, but it is still unable to completely eradicate biofilm [23].

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