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A UVC Device for Intra-luminal Disinfection of Catheters: In Vitro Tests on Soft Polymer Tubes Contaminated with Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Candida albicans

A UVC Device for Intra-luminal Disinfection of Catheters: In Vitro Tests on Soft Polymer Tubes Contaminated with Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Candida albicans
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  A UVC Device for Intra-luminal Disinfection of Catheters:  In Vitro   Testson Soft Polymer Tubes Contaminated with  Pseudomonas aeruginosa  , Staphylococcus aureus  ,  Escherichia coli   and  Candida albicans  Jimmy Bak* 1 , Tanja Begovic 1 , Thomas Bjarnsholt 2 and Anne Nielsen 2 1 Department of Photonics Engineering, Technical University of Denmark (DTU), Roskilde, Denmark 2 Department of International Health, Immunology and Microbiology, Faculty of Health Sciences, University ofCopenhagen, Copenhagen N, Denmark Received 18 March 2011, accepted 8 June 2011, DOI: 10.1111/j.1751-1097.2011.00962.x ABSTRACT Bacterial colonization of central venous catheters (CVCs) causessevere complications in patients. As a result, developing methodsto remove and prevent bacterial and fungal colonization of CVCsis imperative. Recently, we have demonstrated that disinfectionby radiation of polymer tubes with UVC light is possible. In thispaper we present dose–response results using a newly developedUVC disinfection device, which can be connected to a Luercatheter hub. The device was tested on soft polymer tubescontaminated with a pallet of microorganisms, including  Can-dida albicans, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa  ( ca  10 3 CFU mL ) 1 ). The tubes wereequipped with a modified catheter hub and interfaced to thedisinfection device  via  a middle piece separating the disinfectiondevice from the hub. The contamination lasted for 3 h prior totreatment to simulate an aseptic breach. Our results show UVCkilling in a dose and time dependent manner, with no viablecounts after 2 min of radiation for bacteria. Killing of   C. albicans was obtained at >20 min in an UVC absorbing suspension. Webelieve our results to be transferable directly to the clinic, and weare currently working on a setup for clinical trial. INTRODUCTION Infections caused by bacterial and fungal contamination inindwelling catheters, especially in long-term central venouscatheters (CVC), are believed to be responsible for highmorbidity and mortality among hospitalized patients (1). Inaddition, CVC-related infections are an economic burden forhealth care systems (2,3). Consequently, extensive resourcesare being utilized to perform investigations to search forsolutions to prevent bacterial and fungal colonization of catheter tube lumens. We have recently demonstrated that it ispossible to launch UVC light into polymer tubes and disinfecttubes contaminated with both biofilm and planktonic bacteriaof   Pseudomonas aeruginosa  (4,5). The obtained results werebased on an experimental setup in which light from a UVC(265 nm) LED diode equipped with a lens system was focusedand launched into tube openings. The doses required toachieve 100% disinfection (detection limit    3 CFU   ⁄   ml)depended on whether the bacteria were part of a biofilm orin a planktonic state; type of tube polymer and length; andconcentration of the sodium chloride solution. During theexperiments the tubes were sealed with UVC transparentquartz plugs to allow light to be transmitted through the intra-luminal liquid solution. Small doses ( i.e.  short treatment timesspaced a few minutes apart) used preventatively were sufficientfor almost complete disinfection of the intra-luminal space of 20 cm soft polymer ethylene vinyl acetate (EVA) tubes, theshort treatment time might be advantageous if the catheter hasto be used on a daily basis. Strikingly, no hazardous chemicalagents were used and the potential treatment method forcatheter salvage effectively kills  e.g.  biofilm by adjusting thedelivered UVC dose and broad spectrum efficiency,  i.e.  allpathogenic micro-organisms were killed by UVC. UVCtreatment of tubes has also been demonstrated recently byothers. Dai  et al.  managed to reduce the number of planktonicpathogens sampled on the outer surface of semitransparentpolymer tubes with 4–7 logs using a dose of 11 mJ cm ) 2 . TheUVC light source used in their study was a fluorescent lampplaced in the intra-luminal space (6).We present a newly designed and manufactured small UVCdevice for intra-luminal disinfection of catheter hubs andtubes. The LED and other optical and electric parts are anintegrated part of the device, which  via  a middle piece is joineddirectly to a standard Luer female catheter connector. Theseengineered parts can be connected to catheters for disinfectionpurposes and is an extension of the earlier laboratory setupincluding transparent tube plugs (4,5). The effectiveness of thedevice is demonstrated on soft EVA tubes. In our earlierdisinfection work with the LED diodes  P. aeruginosa  was usedas the test micro-organism (4,5). In the work reported here wehave included additional micro-organisms for exemplification.The tubes were contaminated with planktonic  Candida albi-cans, Staphylococcus aureus, Escherichia coli and P. aeruginosa (10 3 CFU mL ) 1 ) for a short period (3 h), simulating an asepticbreach before UVC treatment is initiated with the disinfectiondevice (5,7). The only difference between this treatment and ascheduled treatment is that the UVC is applied directly on thebacterial suspension without flushing and filling with a 0.9%saline solution. This approach is disadvantageous because the *Corresponding author emails:; Bak)   2011 The AuthorsPhotochemistryandPhotobiology  2011TheAmericanSocietyofPhotobiology 0031-8655/11 Photochemistry and Photobiology, 2011, 87: 1123–11281123  bacterial suspension nutrition content absorbs UVC light andconsequently lowers the disinfection efficiency substantially.Testing our method under less optimal light propagationconditions, however, is useful. Other examples of absorbingcompounds that may be found in the intra-luminal space inreal settings are small concentrations of blood, nutrients anddrug residues. In the initial stage of our investigations therewas uncertainty as to how well the CVC catheters wereemptied for possible UVC absorbing compounds during thestandard flushing procedure of the CVCs with 20 mL 0.9%saline solution. In earlier work, we have discovered that EVAtubes are easy to empty for bacteria when flushed with a salinesolution. This is another reason why disinfection is donedirectly on the bacterial and yeast suspensions (5).Detected in catheters causing blood stream infections,  S.aureus  is one of the most frequently observed pathogenicmicro-organism in hospital environments (8), thus making itan obvious choice to include in the test. Also observed as apathogenic micro-organism in many catheter related infections(9),  C. albicans  is larger than the bacteria ( ca  5  l m) andreported in the literature to have a smaller susceptibility toUVC light than many of the bacteria relevant for cathetersepsis. The 99.9% kill dose is reported to be  ca  15–22 mJ cm ) 2 for planktonic  C. albicans  (10). This pathogen might thereforedefine the upper bound of necessary UVC doses to apply tocatheter-like tubes to achieve a sufficient kill rate. Finally, wealso tested a different  P. aeruginosa  strain compared to thatreported in earlier studies as well as an  E. coli   strain. Thepresence of these two micro-organisms in catheters is welldocumented in many reports (1,11). MATERIALS AND METHODS Disinfection device.  Figure 1a shows a sectional view of the prototypeversion of the disinfection device used in this study. The total length of the prototype is 35 mm with an outer diameter of 11 mm. The housingin the current version is made of molded polymer. A UVC transparentquartz window is mounted on top of the device. The surface of thewindow (UV grade quartz 1 mm thickness, UQG Optics Ltd) is inclose contact with the edge of the catheter hub during operation inorder to disinfect the edge of the hub and intra-luminal parts of thecatheter hub properly. The UVC LED light source (275 nm UVTOPLED from Sensor Electronic Technology Inc.) and optical lens areplaced at a distance of 7–8 mm from the catheter hub such that theUVC light intensity is simultaneously focused and launched effectivelyinto the hub opening, sweeping the edge and intra-luminal spaceproperly. The disinfection device is powered by 5–6 V DC using anexternal electrical power supply. The device is connected to thecatheter hub  via  a disposable middle piece. This part has two functions.First, in future clinical applications it can be equipped with a thin UVCtransparent polymer film that acts as both a window and as a barrierbetween the catheter hub and light source (window part). This featureprevents the window on the disinfection device from being contam-inated and reduces the need for cleaning between usages. Second, themiddle piece prevents the device from being joined directly to thecatheter hub. As a result, the device does not need an extendedcoupling. The middle piece is threaded to the catheter hub (12). Thecatheter hub used for the disinfection tests was a standard Luer femaleconnector taken from a commercial catheter, but modified so thatØ6 mm EVA tubes could fit into the distal end of the hub. The hubwas cleaned with 70% of ethanol between uses and joined to the EVAtubes before these were UVC treated. Figure 1b shows the three partsassembled: the disinfection device, middle piece and catheter hub   ⁄   tube. Preparation of test organisms and contamination of tubes.P. aeruginosa  (PAO1 – ATCC),  E. coli   (MT 102),  S. aureus  (13) and C. albicans  (clinical isolate) cultures were used in the experiments.Stock solutions of the cells were made using Luria Bertani (LB) brothcontaining 20% glycerol and stored in vials at  ) 80  C. A fresh culturewas prepared by inoculating one loop of frozen culture in 5 mL of LBbroth (1% tryptone, 1% sodium chloride, 0.5% yeast extract, milli Qwater) from the University of Copenhagen, Faculty of Health Sciencesand incubated for 18 h at 37  C in an orbital shaking incubator at180 rpm (KS 501 digital; IKA  -Werke Gmbh & Co.). After incuba-tion, the bacterial   ⁄   yeast suspension was vortexed for 30 s (MS 2 minishaker, IKA) mixed and the optical density 450  was measured in aspectrophotometer (UV-1800 Shimadzu Scientific Instruments).Theovernight bacterial and yeast suspensions was diluted to 0.1 OD in5mL LB and adjusted to 10 3 CFU mL ) 1 up to 100 mL with 0.9%saline solution in a sterile flask. To obtain the same inoculation level(10 3 CFU mL ) 1 ) for all micro-organisms, 10 and 500  l L were drawnfrom the bacterial and yeast 0.1 OD dilutions, respectively. Thisresulted in a 0.01% LB in the bacterial solutions and a 0.5% LB in theyeast solution. With its higher content of nutrients (0.5% LB), theyeast inoculated suspension is expected to absorb more UV light thanthe more diluted bacterial suspension (0.01% LB). The tubes wereinoculated by sterile injection of the 10 3 CFU mL ) 1 suspensions andsealed with glass plugs. EVA tubes (20 cm tubes from Totax plasticA   ⁄   S, Denmark) and glass plugs were disinfected in 70% ethanol for4–5 h and dried overnight prior to use. After inoculation, the outersurfaces of the tubes were disinfected with 70% ethanol to reduce therisk of contaminating the samples drawn from the intra-luminal spaceafter UVC treatment. The tubes were maintained in a horizontalposition for 3 h at 37  C before initiating UVC treatment. UVC disinfection, dose calculations and CFU counting.  EVA tubeswere used in all of the disinfection tests. Twenty centimeters in length,the outer and inner diameter of the tube was 6 and 4 mm, respectively.The intra-luminal space of the tubes was exposed to UVC light fromthe disinfection device at 2–20 min intervals for bacteria and 2–60 minintervals for  C. albicans . The power emitted from the diode at 275 nmwas measured (Optical Power Meter 1830-C and UV detector Model818 UV, Newport Corporation equipped with OD 3 attenuator) to bebetween 0.42 and 0.45 mW (electrical current:  I  F  = 40 mA) in all theexperiments with bacteria and 1.3 mW ( I  F  = 120 mA) in tests on C. albicans . The maximum output power of the UVC diode is specifiedto be as high as 10 mW, thus leaving ample room for increasing theiroutput and subsequently reducing the treatment time reported in thisstudy substantially (dose = power  ·  time). Figure 2 shows the geo-metry for calculating the UVC doses delivered through the cross-sectional area of the intra-luminal space in both the proximal end (lightlaunching point) and at the distal end (before exit of the catheter). Theexponential damping curve illustrates how the UVC disinfection poweris attenuated during it propagation through the tube.The UVC fluencies that were applied to the tubes during thedisinfection experiments are reported in Tables 2 and 3 as the inputfluence (dose) through the cross-section of the tube and the expectedfluence through the tube cross-section at the far most distal part.The fluence is calculated as the irradiance through ‘‘A’’ (see Fig. 2)multiplied by the exposure time in seconds and is reported here inmJ cm ) 2 units. The critical point is to deliver the necessary UVC dose (a)(b) Figure 1.  (a) Schematic diagram of the disinfection device separatedfrom the middle piece and catheter hub. (b) The assembled device joined to the catheter Luer connector  via  the middle piece. 1124 Jimmy Bak  et al.  in the distal part of the tube. We have measured the input and outputintensities for tubes with 0.9% saline solutions and with 0.5% LBsuspensions with and without bacteria. The reflection from the quartzplugs is  ca  10% and the measured output intensities are thereforemultiplied by 1.1 to estimate the approximate intensity in the far mostdistal part of the tube. The delivered doses can then be calculated andthe killing rates obtained compared to those obtained and reported inthe literature by others.After incubation and UV irradiation of the samples, the number of CFUs was determined for the UVC-treated tubes and control tubes.Liquid samples were drawn from the tubes into sterile vials. The totalvolume of the intra-luminal space was 2.5 mL. Liquid sample sizes of 100  l L were spread directly on LB plates (2% agar, 1% tryptone, 1%sodium chloride, 0.5 yeast extract, milli Q water; University of Copenhagen, Faculty of Health Sciences) or blue plates (for  E. coli  samples: pepton, yeast extract, sodium chloride, lactose, glucose,detergent, bromthymolblue, sodiumthiosulphate; Statens Serum Insti-tut, Copenhagen) and incubated aerobically at 37  C for 24 h. Samplesizes of 400  l L were analyzed for each bacterial species. All of thebacterial samples were analyzed in quadruplicate. The detection limitwas less than 3 CFU mL ) 1 .  C. albicans s ample sizes of 200  l L wereanalyzed (in duplicate) and the detection limit was 5 CFU mL ) 1 . RESULTS Optical beam characteristics The ability to launch the light properly into the tube openingsis important. Figure 3 shows the UVC intensity measuredthrough a 0.1 mm pinhole moved across the beam at rightangles to the optical beam axis and taken at different distancesfrom the diode-ball lens surface. The beam spot is minimizedwhen the distance is  ca  7–8 mm. At larger distances, theintensity distributions flatten out and the light is redistributedaway from the optical axis. The curves show that effectivelylaunching UVC light into narrow tube openings ( ca  1.5–2 mm)is possible with practically no loss. Our UVC disinfectionmethod can thus be applied to many different catheters andtubes sizes. Transmittance of luminal fluids As mentioned in the introduction, the disinfection tests werecarried out on diluted LB suspensions containing the10 3 CFU mL ) 1 micro-organisms. Table 1 shows the calculatedinput power and power at the distal tube end as well astransmittances for 0.9% saline solutions and bacterial suspen-sions containing LB. Note the large drop in Table 1 in powerat the distal end of the saline solutions and the bacteria + LBsuspensions.Table 1 shows that the 0.5% LB bacterial suspensionstrongly absorbs UVC light. The disinfection tests reportedin this article were all performed using the LB solutions shown Figure 2.  The irradiance through a cross-sectional surface in the distalpart of the tube is determined by measuring the output power,  P OUT ;dividing by the cross-sectional area,  A ; and correcting for reflectionlosses:  P OUT   ⁄   A . Figure taken from Bak  et al.  (16). Table 1.  The percentage of UVC light irradiating the distal end of the20 cm EVA tube is low compared to that irradiating the hub andproximal part of the tube. A dramatic decrease in transmittance isobserved for solutions containing only 0.5% LB,  i.e.  3.9% of thetransmittance compared to that of the pure saline solution. Thetransparency of the bacteria-LB suspension is close to that of the puresaline solution (74%).LBsuspension(%)Inputpower(mW)Distalpower(mW)  T   (%)  T  R  (%)0.9% saline solution 0 1.30 0.050 3.8 100Bacteria 0.01 0.43 0.012 2.8 74 Candida albicans  0.5 1.30 0.002 0.15 3.9LB = Luria Bertani; EVA = ethylene vinyl acetate. Table 2.  Results with the three micro-organisms (planktonic) separately present in a 0.01% LB solution using the device preventatively on 20 cmEVA tubes.SamplesFluence attube input(J cm ) 2 )Fluencedistal end(mJ cm ) 2 )Growth in control and UVC-treated samples CFU mL ) 1 (liquid) StaphylococcusaureusEscherichiacoli Pseudomonasaureginosa Control (3) – – 1.6  ·  10 3 (0.2) 3.9  ·  10 3 (0.2) 1.8  ·  10 3 (0.2)2 min UVC (3) 0.41 12.1 No growth No growth No growth5 min UVC (3) 1.03 30.3 No growth No growth No growth10 min UVC (3) 2.05 60.5 No growth No growth No growth15 min UVC (3) 3.08 90.7 No growth No growth No growth20 min UVC (3) 4.11 121.0 No growth No growth No growthNote the different units for fluence (J cm ) 2 and mJ cm ) 2 ). The input fluencies are calculated as: fluence = (0.43 mW  ·  treatment time)   ⁄   0.1256 cm 2 .The output fluencies are calculated as: fluence = (0.011 mW  ·  1.1  ·  treatment time)   ⁄   0.1256 cm 2 . The factor of 1.1 compensates for the  ca  10%reflection loss on the quartz plug at the distal end. All measurements are in triplicate. The numbers in parentheses represent the standard deviationsof the CFU counts.LB = Luria Bertani; EVA = ethylene vinyl acetate. Photochemistry and Photobiology, 2011, 87 1125  in Table 1. After completing the disinfection tests, it wasquestioned what the transmittance would be using the stan-dard procedure followed by Danish hospitals where CVCs areflushed with 20 mL of a 0.9% saline solution before injectionof a lock solution such as heparin.Figure 4 shows the results of flushing two 20 cm EVA tubesinitially filled with a 100% LB solution with varying amountsof milliliters of a pure 0.9% saline solution. The procedure wasrepeated twice for each tube after they had been cleaned with alarge volume of a saline solution. Flushing with only 2.5 mL of 0.9% saline solution ( ca  intra-luminal space volume of the20 cm tubes) leaves the intra-luminal space totally opaque at275 nm. Table 1 shows that the absorption of the 0.5% LBbacterial suspension only transmits 3–4% of the UVC light.Figure 4 shows that this low transmittance is comparable tothe transmittance obtained after flushing tubes with 7–8 mL of 0.9% saline solution that were initially filled with a 100% LBsolution. The curve shows that the UVC transparency of theintra-luminal solution increases dramatically with injection of an additional 2–3 mL of saline solution. The 0.5% LB yeastcell suspension used in the  C. albicans  disinfection testsrepresents a severe case with respect to reduced UVCtransparency. Disinfection of tubes contaminated with bacteria in 0.01 %  LBsolutions Table 2 shows the results of applying the disinfection UVCdevice after the tubes have been subjected to bacterial LBsuspension for 3 h. The CFUs mL ) 1 in the control tubes isconstantly above 10 3 for all three bacteria. No growth wasobserved in any of the UVC-treated tubes. Even for theshortest treatment time (2 min), no viable bacteria werecounted on the plates. It should be emphasized that thenormal UVC disinfection procedure would have included areplacement of the 0.01% LB with reduced transmittance(74%) with a 0.9% saline solution in order to obtain a UVCtransparent media for light propagation.The fluencies measured in the distal end are displayed inunits of mJ cm ) 2 . The smallest dose delivered at the distal end Table 3.  Candida albicans  in 0.5 LB solution.SamplesFluenceat tube input(J cm ) 2 )Fluencedistal end(mJ cm ) 2 )Growth incontrol andUVC-treatedsamplesCFU mL ) 1 (liquid) C. albicans Control (6) – – 2.9  ·  10 2 (0.1)2 min UVC (6) 1.24 2.10 2.5  ·  10 2 (0.2)5 min UVC (6) 3.11 5.25 1.2  ·  10 2 (0.2)10 min UVC (6) 6.21 10.5 2.3  ·  10 1 (0.02)15 min UVC (6) 9.32 15.8 3.3 (0.002)20 min UVC (6) 12.4 21.0 1.7 (0.012)60 min UVC (6) 37.3 63.1 No growthNote the different units for fluence. The input fluencies are calculatedas: fluence = (1.30 mW  ·  treatment time)   ⁄   0.1256 cm 2 . The outputfluencies are calculated as: fluence = (0.002 mW  ·  1.1  ·  treatmenttime)   ⁄   0.1256 cm 2 . The factor of 1.1 compensates for the  ca  10%reflection loss on the quartz plug. The numbers in parenthesesrepresent the standard deviations of the CFU counts. All measure-ments are replicated six times.LB = Luria Bertani. Figure 3.  Diode-lens beam shapes. The most focused spot size isobtained at a distance of   ca  7.5 mm from the diode-ball lens surface. Figure 4.  The transmittance percentage is calculated as the ratio of thepower measured at the distal end (tube output) of tubes filled with LBsolutions to that of the cleaned tubes filled with 0.9% saline solution( T  % = ( I  LB   ⁄   I  SALINE )  ·  100%). The blue and red lines represent twodifferent 20 cm EVA tubes, each of which was processed twice. Thefinal transmittances after flushing with 20 mL were between 90 and96% of the transmittance observed in cleaned, new tubes. The flushingconditions for the two tubes samples represented by the colored lineswere identical. The difference between the curves represents thevariation between experiments. EVA = ethylene vinyl acetate;LB = Luria Bertani. 1126 Jimmy Bak  et al.  (2 min UVC treatment time) is 12 mJ cm ) 2 , which is sufficientfor a more than 99.9% kill of the bacterial species tested. Theresults closely match what has been reported in the literatureand what is available in destruction charts (14). The 0.01% LBsolution attenuates the UVC light compared to that observedin a pure 0.9% saline solution (see Table 1). The slightattenuation, however, only has a minor impact on thetreatment time. Sufficient disinfection is reached within a fewminutes of UVC light exposure. This reduction in treatmenttime, compared to that reported in earlier work on the same20 cm EVA tubes (5), is obtained by using a light source withmuch higher output. Disinfection of tubes contaminated with  C. albicans  in 0.5 %  LB C. albicans  requires slightly larger UVC doses to obtain thesame killing rates as the other bacteria studied in this article(15). Applying the device directly to an absorbing LB bacterialsuspension that has a higher concentration of UVC absorbingcompounds (0.5% LB) is an additional complication. TheLED diode is specified to deliver a high UVC output of up to10 mW, requiring the diode to be cooled. The diode operatedin all of the bacterial tests reported above were used at a safe,low current level (40 mA) that did not require cooling butwhich gave the device a sufficiently high UVC output( ca  0.43 mW). In order to test both the diodes and obtainreasonably low treatment times for  C. albicans  under these lessadvantageous conditions with strong attenuation towards thedistal end of the tubes, we decided to triple the output power of the light source to  ca  1.3 mW by simply increasing the currentlevel to 120 mA (linear relationship between diode current andoutput power). A passive cooling system was added to thedevice by soldering a copper wire to the diode housing toprovide thermal contact to the device’s metal power switch.Table 3 shows the results of the disinfection tests with C. albicans- contaminated EVA tubes. One striking feature isthat the CFU mL ) 1 of the controls was a factor of ten less thanthose of the bacteria even if the CFU mL ) 1 in the flask beforeinjection into the tubes was the same for all of the micro-organisms tested.Figure 5 shows a microscopy of the overnight cell suspen-sion sample. The smaller number of CFUs in the controls for C. albicans  compared to the bacteria seems to indicate thateither the yeast cells do not thrive in the narrow tubes even if nutrients are present  or  the CFU counting of the controls ishampered by cell agglomeration. Table 3 shows that muchhigher doses are required to obtain 100% killing for C. albicans  than for the other organisms. Using the poweroutput measured at the distal end shown in Table 1, thekilling rates for  C. albicans  can be determined. It is possibleto estimate the fluencies   ⁄   doses delivered to this part of thetube and observe which doses are required to obtain 100%kill. The fluencies delivered to the distal end for varioustreatment times are shown in Table 3. We observe no growthfor a dose equal to 63.1 mJ cm ) 2 and a few counts for21 mJ cm ) 2 dose. We conclude that the planktonic solutioncontaining  C. albicans  is disinfected with doses between 20and 60 mJ cm ) 2 . DISCUSSION Clinical features The UVC device presented here has several features thatmake it clinically applicable for intra-luminal disinfection of CVCs. First, the doses required for 100% kill within thedetection limit of initial contaminating bacteria can bedelivered in a few short minutes even in soft tubes that guideUVC light poorly. The LED diodes utilized in this study arespecified to run at an even higher output power, which meansthat reducing the treatment time even more is possible. Inaddition, the disinfection device, which is easy to connect to astandard Luer catheter hub, is equally efficient against allpathogenic micro-organisms relevant for CVC-related bloodstream infections. We tested the device under less thanoptimal conditions where an absorbing nutrient, LuriaBertani, was present. The normal flushing procedures with10–20 mL of 0.9% saline solution improved the transmittanceof the intra-luminal space such that the treatment times wereshort and also clinically relevant. As the flushing proceduresare part of the maintenance of CVCs, the UVC disinfectionshould be applied before anticoagulating lock solutions suchas heparin are injected. If residues remain in the CVCs afterflushing, for instance, blood cells and proteins in CVCs usedfor hemodialysis, the treatment time can be adjusted so therequired dose for 100% kill is delivered to the entire intra-luminal space of the tube. Notably, the device more or lessinstantaneously disinfects the hub and first part of the  ex-vivo part of the CVC due to the high power level at the proximalpart of the tube. The device could then also be used solely forhub disinfection.The spot size of the UVC light beam from the disinfectiondevice can be narrowed down to 1.5–2 mm, which means it canbe launched into small tube openings with next to no loss of power. This makes the device applicable to all kinds of CVCs. Figure 5.  Candida albicans  cells in (0.5%) LB suspension (100 · ,oil immersion). The cells agglomerate and budding is observed.LB = Luria Bertani. Photochemistry and Photobiology, 2011, 87 1127
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