Presentation on theme: "Cl Brandon Childers 1, Clare McCoy 2, Karl Malcolm 2 & Alexandra C. Brand 1 1.Aberdeen Fungal Group, School of Medical Sciences, University of Aberdeen,"— Presentation transcript:
cl Brandon Childers 1, Clare McCoy 2, Karl Malcolm 2 & Alexandra C. Brand 1 1.Aberdeen Fungal Group, School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, UK 2. School of Pharmacy, Queen's University Belfast, Belfast, BT9 7BL, Northern Ireland, UK. References Acknowledgements 50 µm Characterization and inhibition of medical silicone biofouling by Candida spp. in mixed-species biofilms Soft silicones are used for the manufacture of indwelling medical devices such as PEG tubes, gastronasal tubes and voice prostheses, which require frequent replacement due to the build-up of mixed-species biofilms, which obstruct device function (1,2). From a clinical prosthetic device, we isolated 3 bacteria (Proteus mirabilis, Klebsiella oxytoca, and Micrococcus luteus) and 2 Candida species (dubliniensis, and parapsilosis) in order to investigate interactions between co-colonising species and optimise assays to evaluate antimicrobial medical silicones developed by our collaborators. In planktonic culture, individual bacteria demonstrated antagonistic effects against C. dubliniensis and C. parapsilosis, in a manner similar to that observed between P. aeruginosa and C. albicans (3). The antagonistic effects were abrogated in the context of a mixed-species biofilm. A robust biofilm composed of all five organisms, recapitulating the original explant biofilm, was established over the course of six weeks. To test our hypothesis that silicone modified with mobile head groups would reduce microbial adhesion, a hydrophilic, linear polymer (AMPEG450) was grafted to Nusil silicone and tested for microbial colonisation in vitro. Initial adhesion of Candida spp and bacteria was reduced by 90% and 70 %, respectively, on the modified silicone. Biofilm formation after 48 h by C. albicans was also significantly decreased compared to unmodified Nusil. This model will be used to further characterize the mechanisms involved in medical polymer biofouling and assess a range of silicone-modification strategies to inhibit biofilm formation and thereby increase the useful life of medical devices. fjfj 4. Five clinical co-isolates form a robust biofilm in vitro 5. Silicone surface modification inhibits adhesion and biofilm formation 3. In biofilms, fungi co-exist with antagonistic bacteria 6. Summary & conclusions Introduction During growth as planktonic cells, bacterial explant isolates exhibit antagonism in a growth-condition-dependent manner against Candida spp isolated from the same device. Bacteria-Candida antagonistic effects are abrogated in biofilms. Single-species biofilms form poorly compared to multi-species biofilms (Fig. 6). Production of a robust and stable in vitro mixed-species biofilm requires ‘reseeding’. The stability of biofilms containing C. albicans may involve hyphal anchoring within the silicone substratum. Silicone surface modification using mobile end-groups shows potential as a method of reducing microbial adhesion and the rate of biofilm formation. A B C A B 2. Variable ability of bacteria and Candida spp to form single-species biofilms A. C. B. Figure 2. A. Candida spp. adhesion to silicone was assessed by incubation of a 1.5 cm 2 silicone coupon in RPMI medium containing 10 6 cells/mL at 37°C for 40 min. Adhered cells were enumerated by light microscopy from 10 randomly selected visual frames. B. Bacterial adhesion to silicone was assessed by incubation of a 1.5 cm 2 silicone coupon in RPMI medium containing 10 7 cells/mL at 37°C for 4 h. Cells were removed from the silicone and CFUs determined per coupon. C. Biofilms formed by individual species generated in tryptic soy broth using 10 6 cells/ml yeast and 10 7 cells/ml bacteria in a 96 well microtiter plate. Plates were incubated at 37°C for 48 h and biomass quantified by crystal violet staining. 1. Bacterial killing of Candida spp. in planktonic culture Figure 1. Candida dubliniensis or C. parapsilosis yeast cells (10 6 cells/mL) were inoculated into 10 mL RPMI-1640 or YPD and incubated for 3 h at 37°C or 30°C, to produce hyphae or yeast cells, respectively. Cultures were incubated for 7 days at 37°C or 30°C after addition of 2.5mL of a midlog culture of bacterial cells (P. aeruginosa, P. mirabilis, K. oxytoca, or M. luteus). Hypoxic conditions were created by withholding oxygen from cultures grown under hypha-inducing conditions (RPMI, 37°C). The viable fungal cell population was determined daily by plating on YPD solid medium containing antibacterial agents. Figure 4. A five-species biofilm was formed in artificial saliva medium using an initial inoculum of 10 6 cells/ml/yeast and 10 7 cells/ml/bacteria in a culture flask containing a 1.5 cm 2 silicone coupon. Cultures were incubated for 6 weeks at 37°C. The medium was replaced once each week and ‘re-seeded’ with fungal and bacterial species. A. Biofilms were mechanically disrupted and the cell suspension used to determine CFUs on bacterial selective media and/or YPD containing antibiotics. B. Mixed- species biofilm formation was visually assessed by scanning electron microscopy. Figure 5. The medical silicone, Nusil, was modified by the addition of mobile, long-chain head- groups using a novel grafting method. A. Candida spp. adhesion to Nusil and AMPEG450 was assessed by incubation of 1.5 cm 2 silicone coupons in RPMI media containing 10 6 cells/mL at 37°C for 40 min. Adhered cells were enumerated by light microscopy, using 10 randomly selected visual frames. B. Bacterial adhesion to the silicones was similarly assessed in RPMI medium containing 10 7 cells/mL with incubation at 37°C for 4 hours. Adhesion was quantified by determining CFUs on selective media to determine number of cells per silicone coupon. C. C. albicans biofilms were formed on the silicones in RPMI medium, as above. Biofilms were incubated at 37°C for 48 hours and biomass assessed by crystal violet staining. 1. Ramage, G., Martinez, J.P., and Lopez-Ribot, J.L. (2006). Candida biofilms on implanted biomaterials: a clinically significant problem. FEMS yeast research 6, 979-986. 2. Ticac, B., Ticac, R., Rukavina, T., Kesovija, P.G., Pedisic, D., Maljevac, B., and Starcevic, R. (2010). Microbial colonization of tracheoesophageal voice prostheses (Provox2) following total laryngectomy. European archives of oto-rhino-laryngology 267, 1579-1586. 3. Brand, A., Barnes, J.D., Mackenzie, K.S., Odds, F.C., and Gow, N.A. (2008). Cell wall glycans and soluble factors determine the interactions between the hyphae of Candida albicans and Pseudomonas aeruginosa. FEMS Microbiology Letters 287, 48-55 No overall correlation between initial adhesion and biofilm formed at 48 h. The clinical isolates formed poor biofilms compared to the two laboratory strains, C. albicans SC5314 and P. aeruginosa PA01... In yeast growth conditions, C. parapsilosis but not C. dubliniensis was sensitive to P. mirabilis. Hypha formation correlates with susceptibility of C. dubliniensis to killing by 3 bacteria. Under hypoxic conditions, P. aeruginosa did not kill C. dubliniensis but P. mirabilis killed both Candida spp.... ‘Re-seeding’ of biofilms was required for the establishment of a stably-attached structure, suggesting that in vivo biofilms may result from more than one infective exposure event. Biofilms formed by the five co-isolates were densely- structured. Although higher, the numbers of cells present at 6 weeks was in proportion to the number of cells present at 48 h... Cross-section of a 6-week-old C. albicans biofilm formed on silicone elastomer. Blue fluorescent strain courtesy of Karen Strijbus. C. dubliniensesC. parapsilosis BAC Figure 3. A and B. Combinations of ex-plant species were used to form biofilms in tryptic soy broth using an initial inoculum of 10 6 cells/ml yeast and 10 7 cells/ml bacteria in a 96-well plate. Cultures were incubated for 48 h at 37°C. Biofilms were mechanically disrupted and fungal CFU determined by growth on YPD containing antibiotics. C. A 48 hour biofilm was formed using the 5 ex-plant species in artificial saliva in a culture flask containing a 1.5 cm 2 silicone coupon. Biofilms were mechanically disrupted and CFU determined by plating on bacterial selective media and/or YPD containing antibiotics. Composition of biofilm on silicone C. dubliniensis is less abundant in the present of bacteria than C. parapsilosis. C. dubliniensis remains viable in biofilms in the presence of the 3 bacteria that killed it in planktonic conditions... Figure 6: A 6-week-old single-species C. albicans biofilm formed on silicone elastomer. Adhesion by Candida sppAdhesion by bacteriaBiofilm formed by C. albicans Adhesion was reduced by 90 % for Candida spp and by 70 % for the 3 bacterial species co-isolated from the voice prosthetic. C. albicans biofilm film formation by was reduced by 75 % on AMPEG450 silicone compared to untreated Nusil...
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