Escherichia coli is the best characterized bacterium; it grows rapidly, and it is easy to manipulate genetically. An increased knowledge about the physiology of this model organism will facilitate the development of engineered E.coli strains for applications such as production of biofuels and biofilm control. The aims of this work were the application of protein engineering to increase E. coli hydrogen production, the identification of the proteins regulating extracellular DNA production (eDNA), and the evaluation of the effect of the proteins synthesizing the signal 3'-5'-cyclic diguanylic acid (c-di-GMP) on biofilm formation. The Escherichia coli hydrogen production rate was increased 9 fold through random mutagenesis of fhlA. Variant FhlA133 (Q11H, L14V, Y177F, K245R, M288K, and I342F) enhances hydrogen production by increasing transcription of the four transcriptional units regulated by FhlA. The amino acid replacements E363G and L14G in FhlA increased hydrogen production 6 fold and 4 fold, respectively. The complete E. coli genome was screened to identify proteins that affect eDNA production. The nlpI, yfeC, and rna mutants increased eDNA production and the hns and rfaD mutants decreased eDNA production. Deletion of nlpI increases eDNA 3 fold while overexpression of nlpI decreases eDNA 16 fold. Global regulator H-NS is required for eDNA with E. coli since deletion of hns abolished eDNA production while overexpression of hns restored eDNA to 70 percent of the wild-type levels. Our results suggest that eDNA production in E. coli is related to direct secretion. Deletions of the genes encoding the diguanylate cyclases YeaI, YedQ, and YfiN increased swimming motility and eDNA as expected for low c-di-GMP levels. However, contrary to the current paradigm, early biofilm formation increased dramatically for the yeaI (30 fold), yedQ (12 fold), and yfiN (18 fold) mutants. Hence, our results suggest that c-di-GMP levels should be reduced for initial biofilm formation because motility is important for initial attachment to a surface.

<p>Biofilms are communities of sessile microorganisms attached to a surface and imbeddedin a matrix of extracellular polysaccharide substances. These communities can be foundin diverse aquatic environments, such as in industrial pipes and in humans. By formingmicrocolony structures, which are highly resistant to adverse physical conditions as wellas antimicrobial agents, biofilms are very problematic when associated with e.g.persistent infections. In order to find new ways of controlling biofilm growth, theprocesses involved in biofilm development must be investigated further. The maininterest of this study is the occurrence of void formation inside biofilms. Thisphenomenon has been observed in several studies and has been correlated to cell deathinside the microcolonies. The occurrence of cell death has recently been associated withthe presence of nitric oxide in the biofilm. In this study, the implications of nitric oxideaccumulation on biofilm development were investigated using an individual-basedmodel. Specifically, the role of nitric oxide in void formation was considered. A largenumber of simulations were run using different parameter settings in order to determine ifnitric oxide could account for the occurrence of void formation observed experimentally.The general predictions made by the model system showed agreement to someexperimental data, but not to others. Sloughing, the detachment of chunks of cells fromthe biofilm, was observed in the majority of simulations. In some cases, the model alsopredicted the presence of live cells inside the voids, which has been observedexperimentally.</p>

Biofouling, or the formation of biofilm on membrane surfaces, can decrease the performance (decreased flux and/or increased operating pressure) of a reverse osmosis (RO) membrane system in a water treatment plant. However, biofilms have been used in water treatment systems to remove organic carbon from water via biofilters and successfully reduce biofilm growth downstream. This research investigates the possibility that the heterotrophic biofilm present on membrane surfaces removes nutrients from the treatment water, thereby making it nutrient deprived as it travels along the treatment train. This may potentially be exploited as an in situ biofilter to actively remove dissolved organic carbon (DOC) from the treatment water, thereby protecting downstream membrane surfaces from biofouling. Analysis of fouled membranes from the Dunedin water treatment plant in Dunedin, FL indicates the presence of biofilm on membrane surfaces in a gradient pattern with a higher level of fouling at the front of the element. Additionally, the community structure of the biofilm at the front of the element is unique with respect to the feed-water and downstream membrane material. Additionally, a carbon (and nitrogen) mass balance study was performed at the water treatment plant in Dunedin, FL through extensive sampling of DOC at multiple locations of the RO membrane system over a 20 month period. Plant-level mass balance results indicate a significant pool of DOC was consistently unaccounted for, and presumably assimilated or otherwise removed within the membrane system. Sampling also indicated a removal of total nitrogen. Additionally, the specific UV absorbance (SUVA) of the DOC in concentrate was consistently greater than that of the feed water, suggesting the removal of labile aliphatic carbon as the feed water travels through the feed channel of the membrane system. A pilot system was designed and built to operate under plant conditions (flow rate and pressure) to test if the biofilm on the surface of the membrane can have a protective effect for downstream membrane material. A fouled membrane element was pulled from the plant at the same time and general location as an autopsied element (to determine composition on the surface) and used in the pilot system. Feed and concentrate water from the pilot was directed to flat sheet modules for performance testing and surface characterization. This allowed for characterization of the two sections without disturbing the membrane element. Differences in performance and foulant deposition were characterized for the two sections as a function of carbon addition and flow rate. The results from this testing suggest the membrane element, or the biofilm on its surface, has both a performance and a foulant deposition benefit for downstream membranes as compared to feed membrane material. This benefit also displayed an increasing trend as the concentration of organic carbon fed into the system increases.

Integrated aquaculture systems (IAS) are a type of recirculating aquaculture systems (RAS) where the wastewater is treated and returned to the fish tanks. The important difference between the two is that in an IAS, wastes from the aquaculture component are recovered as fertilizer to produce an agricultural product whereas in an RAS, waste organics, nutrients and solids are treated and discharged. A pilot marine IAS at Mote Aquaculture Research Park in Sarasota, FL was studied for this project. Water quality monitoring, measurements of fish health and growth rates of fish and plants were performed over a two-year period to determine the effectiveness of the system in producing fish and plant products and removing pollutants. The goal of this portion of the project was to develop, calibrate and evaluate a model of the system, to understand the nitrogen transformations within the Mote IAS and to investigate other potential configurations of the Mote IAS. The model was divided into the various compartments to simulate each stage of the system, which included fish tanks, a drum filter for solids removal, and moving bed bioreactor (MBBR) for nitrification and disinfection. A solids tank after the drum filter was used to store the drum filter effluent slurry, which was then divided between three treatment processes: a geotube, a sand filter followed by a plant bed, and a plant bed alone. Nitrogen species modeled were particulate organic nitrogen (PON), dissolved organic nitrogen (DON), ammonium and nitrate. Of the physical components of the IAS, models of the MBBR and the two plant raceways included physical, chemical and biological nitrogen transformation processes. The sand filter, solids tank and geotube models were simple mass balances, incorporating factional removals of each species based on the observed data. Other variables modeled included temperature, dissolved oxygen, volatile suspended solids and chemical oxygen demand concentrations. The model was built in a computer program, STELLATM, to simulate the Mote IAS. The model calibration involved experimental, literature and calibrated parameters. Parameters were adjusted until the model's output was a best fit to the observed data by minimizing the sum of the squared residuals. During the sensitivity analysis, two model parameters caused large variations in the model output. The denitrifier constant caused the most variation to the model's output followed by the denitrifier fraction of volatile suspended solids. Of the removal processes, denitrification was the largest nitrogen removal mechanism from the model, accounting for 59% and 55% of the nitrogen removed from the south and north plant raceways respectively. Plant and soil uptake represented only 0.2% of the overall nitrogen removal processes followed by 0.1% by sedimentation. Finally, the model was used to investigate other treatment designs if the Mote IAS was redesigned. The first option involved a geotube and one plant raceway in series to treat the solid waste while the second option did not have a geotube, but two plant raceways. The first option was the most effective at removing nitrogen while the second was as effective as the original system and would cost less.

Microbial colonization on the surface of silicone rubber high voltage outdoor insulators often results in the formation of highly hydrated biofilm that influence the surface properties, such as surface hydrophobicity. The loss of hydrophobicity might lead to dry band formation, and, in the worst cases, flashover and failure of the insulator. In this work, the biocidal effects of various antimicrobial compounds in silicone rubber materials were determined. These materials were evaluated according to an ISO standard for the antimicrobial activity against the growth of aggressive fungal strains, and microorganisms that have been found colonizing the surfaces of outdoor insulators in several areas in the world. Several compounds suppressed microbial growth on the surfaces of the materials without compromising the material properties of the silicone rubber. A commercial biocide and thymol were very effective against fungal growth, and sodium benzoate could suppress the fungal growth to some extent. Thymol could also inhibit algal growth. However, methods for preservation of the antimicrobial agents in the bulk of the material need to be further developed to prevent the loss of the compounds during manufacturing. Biofilm formation affected the surface hydrophobicity and complete removal of the biofilm was not achieved through cleaning. Surface analysis confirmed that traces of microorganisms were still present after cleaning. Further, surface modification of the silicone rubber was carried out to study how the texture and roughness of the surface affect biofilm formation. Silicone rubber surfaces with regular geometrical patterns were evaluated to determine the influence of the surface texture on the extent of microbial growth in comparison with plane silicone rubber surfaces. Silicone rubber nanocomposite surfaces, prepared using a spray-deposition method that applied hydrophilic and hydrophobic nanoparticles to obtain hierarchical structures, were studied to determine the effects of the surface roughness and improved hydrophobicity on the microbial attachment. Microenvironment chambers were used for the determination of microbial growth on different modified surfaces under conditions that mimic those of the insulators in their outdoor environments. Different parts of the insulators were represented by placing the samples vertically and inclined. The microbial growth on the surfaces of the textured samples was evenly distributed throughout the surfaces because of the uniform distribution of the water between the gaps of the regular structures on the surfaces. Microbial growth was not observed on the inclined and vertical nanocomposite surfaces due to the higher surface roughness and improved surface hydrophobicity, whereas non-coated samples were colonized by microorganisms. / <p>QC 20151002</p>

Algae are photosynthetic microorganisms that convert carbon dioxide and sunlight into biomass that can be used for biofuel production. Although they are usually cultivated in suspension, these microorganisms are capable of forming productive biofilms over substrata given the right conditions. This dissertation focuses on algal biofilms and their application in biofuel feedstock production. In particular it reports the construction and performance of an algae biofilm photobioreactor, the physico-chemical surface properties of different algal species and adhesion substrata, and cell-surface interactions based on experimental results and theoretical models. A novel algae biofilm photobioreactor was constructed and operated (i) to demonstrate the proof of concept, (ii) to analyze the performance of the system, and (iii) to determine the key advantages and short comings for further research. The results indicated that significant reductions in water and energy requirements were possible with the biofilm photobioreactor. Although the system achieved net energy ratio of about 6, the overall productivity was low as Botryococcus branunii is notoriously slow growing algae. Thus, further studies were focused on identification of algal species capable of biofilm growth with larger biomass and lipid productivities. Adhesion of cells to substrata precedes the formation of all biofilms. A comprehensive study has been conducted to determine the interactions of a planktonic and a benthic algal species with hydrophilic and hydrophobic substrata. The physico-chemical surface properties of the algal cells and substrata were determined and using these data, cell-substrata interactions were modeled with the thermodynamic, Derjaguin, Landau Verwey, Overbeek (DLVO) and Extended Derjaguin, Landau, Verwey, Overbeek (XDLVO) approaches and critical parameters for algal adhesion were identified. Finally, the adhesion rate and strength of algal species were quantified with parallel plate flow chamber experiments. The results indicated that both cell and substrata surface hydrophobicity played a critical role for the adhesion rate and strength of the cells and XDLVO approach was the most accurate model. Finally, based on these findings the physico-chemical surface properties of ten algal species and six substrata were quantified and a screening was done to determine algae species substratum couples favoring adhesion and biofilm formation. / text

<p>There are over 30 million Foley urinary catheters used annually, and the greatest problem with Foley catheters is catheter-associated urinary tract infections (CAUTIs). CAUTIs are the number one cause of hospital-acquired infections and make up to 40% of nosocomial infections. Biofilms on urinary catheters are critical to the progression of symptomatic CAUTIs, but are difficult to treat due to the protective effect of the biofilm matrix against antibiotics. The anti-fouling catheter technology proposed and demonstrated herein uses a mechanical, non-antibiotic approach to physically remove biofilms and thereby provide an appealing option for potentially stopping the progression of symptomatic infections. Additionally, because the anti-fouling technology is mechanical, it can circumvent the persistent failings of chemical and biological approaches that have failed to address catheter-associated urinary tract infections for the last 50+ years since Foley catheters were introduced. </p><p>We designed and optimized urinary catheter prototypes capable of on-demand removal of biofilms from the previously-inaccessible main drainage lumen of catheters. The concept uses pressure-actuated chambers in elastomer constructs to generate regio-selective strain and thereby remove biofilms. We first grew mature Proteus mirabilis crystalline biofilms on flat silicone elastomer substrates, and showed that application of strain to the substrate debonded the biofilm, and that increasing the strain rate increased biofilm detachment. A quantitative relationship between the applied strain rate and biofilm debonding was found through an analysis of the biofilm segment length and the calculated driving force for debonding. We then constructed proof-of-concept prototypes of sections of anti-fouling catheter shafts using silicone and 3D printed reverse molding in methods akin to those used for soft robotics. The proof-of-concept prototypes demonstrated release of mature P. mirabilis crystalline biofilms from their strained surfaces, and prompted our development of more advanced multi-lumen prototypes. The multi-lumen prototypes were designed and optimized using successive rounds of finite element modeling to adjust the number and postion of intra-wall inflation lumens. We then constructed prototypes based on the optimized design with clinically relevant dimensions and showed they were able to generate greater than 30% strain on the majority of the luminal surface, and along their full length. Those catheter prototypes were able to on-demand, and repeatedly, remove greater than 80% of a mixed community biofilm of P. mirabilis and E. coli. In summary, this study shows (1) strain in the elastomeric substrate actively debonds crystalline biofilms in vitro (2) modeling based on characterization of biofilm properties and understanding of substrate strain informs and facilitates prototype catheter design (3) urinary catheter prototypes utilizing inflation-induced substrate strain are capable of on-demand and repeatedly removing biofilms in vitro.</p> / Dissertation

The Tay estuary is situated on the east coast of Scotland. The estuary is dominated by sediment biotopes, including mudflats which support sparse beds of two nationally scarce seagrass species, Zostera marina var. angustfolia (Hornem.) and Z. noltii (Hornem.). Seagrasses have been described as ecosystem engineers, shaping their sediment environment, and this may increase sediment deposition and stability. In this thesis the ecosystem engineering characteristics of seagrass habitats are explored. In 2008, the distribution of Zostera spp. in the Tay estuary was surveyed and mapped for the first time. Sediments within beds of Z. marina and Z. noltii were compared to investigate the influence of seagrasses on sediment characteristics. To explore the role of seagrass in sediment deposition and erosion, and coastal stability, sediment depth measurements were made in patches of Z. noltii, Z. marina and bare sediment over one year. The role of the root/rhizome system on sediment retention over winter was also considered. Sediment deposition in Z. noltii beds, and the influence of the plants on near-bed flow dynamics was further explored in the laboratory, using an 8 m seawater flume. In the field the retention of particles over 2 and 14 tides was measured, and the results of this experiment led to a study of the influence of leaf and sediment biofilms on particle retention, using the novel method of magnetic particle induction (MagPI). The efficacy of artificial seagrass beds and Z. noltii transplantation as habitat restoration techniques were compared over one year. During the trial, sediment deposition and changes in sediment characteristics were determined, and the protection given to saltmarsh cliffs fringing the study plots was assessed. Mechanisms underlying the results are suggested and the findings discussed. This study provides an insight into the ecology of seagrass in the Tay estuary and its role as an ecosystem manager. It may offer valuable data which could be utilised for future conservation policies, habitat restoration schemes and management planning of the area.

Bacteria primarily exist in robust, surface-associated communities known as biofilms, ubiquitous in both natural and anthropogenic environments. Mature biofilms resist a wide range of biocidal treatments and pose persistent pathogenic threats. Treatment of adherent biofilm is difficult, costly, and, in medical systems such as catheters, frequently impossible. Adding to the challenge, we have discovered that biofilm can be both impenetrable to vapors and extremely nonwetting, repelling even low surface tension commercial antimicrobials. Our study shows multiple contributing factors, including biochemical components and multiscale reentrant topography. Reliant on surface chemistry, conventional strategies for preventing biofilm only transiently affect attachment and/or are environmentally toxic. In this work, we look to Nature’s antifouling solutions, such as the dynamic spiny skin of the echinoderm, and we develop a versatile surface nanofabrication platform. Our benchtop approach unites soft lithography, electrodeposition, mold deformation, and material selection to enable many degrees of freedom—material, geometric, mechanical, dynamic—that can be programmed starting from a single master structure. The mechanical properties of the bio-inspired nanostructures, verified by AFM, are precisely and rationally tunable. We examine how synthetic dynamic nanostructured surfaces control the attachment of pathogenic biofilms. The parameters governing long-range patterning of bacteria on high-aspect-ratio (HAR) nanoarrays are combinatorially elucidated, and we discover that sufficiently low effective stiffness of these HAR arrays mechanoselectively inhibits ~40% of Pseudomonas aeruginosa biofilm attachment. Inspired by the active echinoderm skin, we design and fabricate externally actuated dynamic elastomer surfaces with active surface microtopography. We extract from a large parameter space the critical topographic length scales and actuation time scales for achieving nearly ~80% attachment reduction. We furthermore investigate an atomically mobile, slippery liquid infused porous surface (SLIPS) inspired by the pitcher plant. We show up to 99.6% reduction of multiple pathogenic biofilms over a 7-day period under both static and physiologically realistic flow conditions—a ~35x improvement over state-of-the-art surface chemistry, and over a far longer timeframe. Moreover, SLIPS is shown to be nontoxic: bacteria simply cannot attach to the smooth liquid interface. These bio-inspired strategies significantly advance biofilm attachment prevention and promise a tremendous range of industrial, clinical, and consumer applications. / Engineering and Applied Sciences

Σκοπός της παρούσας ερευνητικής εργασίας ήταν η επιδημιολογική μελέτη των σταφυλοκοκκικών λοιμώξεων από πηκτάση–αρνητικούς σταφυλοκόκκους (CNS) σε ασθενείς της Μονάδας Εντατικής Θεραπείας των πρόωρων νεογνών του Πανεπιστημιακoύ Γενικού Νοσοκομείου Πατρών (ΠΓΝΠ) μεταξύ 2002-2004. Κατά τη διάρκεια της μελέτης, συλλέχθηκαν συνολικά 287 στελέχη CNS. Τα στελέχη ελέγχθηκαν για την παραγωγή της πρωτεΐνης PBP2α και την ύπαρξη του γονιδίου mecA για τον προσδιορισμό των ανθεκτικών στη methicillin στελεχών CNS. Από το σύνολο των 287 CNS, τα 132 (46%) χαρακτηρίσθηκαν ως MRCNS. Τα MRCNS αποτελούν σοβαρό πρόβλημα για τα νοσοκομεία, γιατί αυξάνουν τον χρόνο παραμονής των ασθενών στο νοσοκομείο, άρα και το κόστος νοσηλείας και θεραπείας. Έγινε μελέτη του φαινοτύπου αντοχής των στελεχών σε αντιβιοτικά, της κλωνικής τους διασποράς και της ικανότητάς παραγωγής βιομεμβράνης σε σύγκριση με την παρουσία των γονιδίων του οπερονίου ica. Για την επιδημιολογική μελέτη των λοιμώξεων που οφείλονται σε MRCNS, μέθοδος αναφοράς είναι η PFGE, κυρίως σε συνδυασμό και με υβριδισμό του χρωμοσωμικού DNA με ειδικούς ανιχνευτές. Όλα τα στελέχη MRCNS ήταν πολυανθεκτικά και η πλειονότητά τους παρήγαγε βιομεμβράνη (89%). Μεταξύ των 115 στελεχών S. epidermidis αναδείχθηκε ένας κυριάρχος κλώνος (z) (77 στελέχη) και ακολούθησε ο κλώνος (g). Τα δέκα από τα δεκαέξι στελέχη του είδους S. haemolyticus ανήκαν στον κλώνο (y). Το οπερόνιο ica συμβάλλει στην παραγωγή της εξωκυττάριας ουσίας polysaccharide-intercellular-adhesin (ΡΙΑ) που είναι το κύριο συστατικό του biofilm. Η έκφραση των γονιδίων του οπερονίου ica επάγεται από την παρουσία του ρυθμιστικού γονιδίου sarA, ενώ καταστέλλεται από το γονίδιο icaR. Τα περισσότερα στελέχη που ήταν biofilm-θετικά (80%) έφεραν όλα τα γονίδια του οπερονίου ica και το τρανσποζόνιο IS256, ενώ τα υπόλοιπα 23 είχαν ποικίλους συνδυασμούς των γονιδίων. Η παρουσία όλων των γονιδίων του οπερονίου ica ανιχνεύθηκε σε τρία από τα δεκαπέντε biofilm-αρνητικά στελέχη. Αναδείχθηκαν ένας κύριος και δύο δευτερεύοντες biofilm-θετικοί, πολυανθεκτικοί MRCNS κλώνοι, που αποίκισαν και προξένησαν λοιμώξεις στα πρόωρα νεογνά. Μέρος της παρούσας ερευνητικής εργασίας ήταν η διερεύνηση της επίδρασης του χρόνου επώασης στη γονιδιακή έκφραση σε δεκατέσσερα αντιπροσωπευτικά στελέχη. Αυτό έγινε μέσω της ποσοτικοποίησης με αλυσιδωτή αντίδραση πολυμεράσης πραγματικού χρόνου (RT-PCR) των γονιδίων icaA και icaD τα οποία κυρίως σχετίζονται με την παραγωγή biofilm, καθώς και δύο ρυθμιστικών γονιδίων icaR και sarA σε σύγκριση με ένα συντηρημένο γονίδιο αναφοράς (23S rDNA). Ο έλεγχος έγινε σε στελέχη S. epidermidis που ήταν ανθεκτικά στη methicillin, κατατάσσονταν σε διαφορετικούς κλώνους, εμφάνιζαν διαφορετικό φαινότυπο σύνθεσης βιομεμβράνης και έφεραν ποικίλους συνδυασμούς γονίδιων. Οι αντιδράσεις απόλυτης ποσοτικοποίησης έκφρασης των γονιδίων είχαν υψηλή απόδοση (1,86 και 1,84 για την επώαση στις τέσσερις ώρες και δύο ώρες, αντίστοιχα). Η μαθηματική ανάλυση δεν έδειξε ιδιαίτερα μεγάλες διαφορές μεταξύ των αποτελεσμάτων για τα τέσσερα γονίδια και τους δύο χρόνους επώασης. Αυτό που παρατηρήθηκε ήταν οτι η έκφραση ήταν υψηλότερη στα biofilm-θετικά στελέχη. Προκειμένου να μελετηθεί η επίδραση της βακτηριακής προσκόλλησης στις διάφορες επιφάνειες τροποποιημένου και μη τροποποιημένου γυαλιού, πραγματοποιήθηκαν δυναμικά πειράματα, κάτω από δύο διαφορετικές συνθήκες ροής, σε δύο χρόνους επώασης σε τέσσερα στελέχη S. epidermidis. Η βακτηριακή προσκόλληση, η παραγωγή biofilm και ο σχηματισμός βιομεμβράνης στις τροποποιημένες επιφάνειες ήταν αυξημένα σε σχέση με τις μη τροποποιημένες. Αυτό ήταν σε συμφωνία με τα αποτελέσματα της γονιδιακής έκφρασης των γονιδίων icaA και icaD, μετά από ανάλυση της έκφρασης των γονιδίων icaA και icaD με RT-PCR, που έδειξε αυξημένες τιμές στις τροποποιημένες επιφάνειες, κυρίως στην υψηλή ροή. Επομένως, ο συνδυασμός της δράσης της χημείας της επιφάνειας και της ροής, επηρεάζουν την προσκόλληση, τον φαινότυπο και το γονότυπο των βακτηριακών στελεχών, όπως και την προσαρμογή τους στις αλλαγές του περιβάλλοντος. Η μελέτη της γονιδιακής έκφρασης μπορεί να βοηθήσει στην κατανόηση των αλληλεπιδράσεων της βακτηριακής προσκόλλησης με το βιοϋλικό. / A total of 132 methicillin-resistant coagulase-negative staphylococci (MRCNS) isolated from preterm neonates were studied for antibiotic resistance patterns, clonal distribution and biofilm formation in relation to the presence of ica operon. All MR-CNS were multi-resistant while the majority (89%) produced biofilm. Among 115 Staphylococcus epidermidis, a major clone (z) was identified (77 strains), followed by clone g. Ten out of 16 S. haemolyticus belonged to a common clone (y). Most of the biofilm-positive strains (80%) possessed all tested genes, while the remaining 23 had a variety of gene combinations. Presence of the entire ica cluster was detected in three out of 15 biofilm-negative strains. One major and two minor biofilm-positive, multi-resistant MRCNS clones were disseminated, colonizing and infecting hospitalized preterm neonates. Fourteen representative MR- S. epidermidis strains were selected and investigated for the expression of icaA and icaD genes, and two regulatory genes, icaR (repressor) and sarA (inducer), towards a housekeeping gene (23SrDNA), by Real-Time PCR (RT-PCR). These strains belonged to various clones, had different combinations of ica genes and biofilm-forming phenotypes. The experiments were performed in two incubation times, after two and four hours. Νο differences were observed at the gene expression level at the two tested times. In general, biofilm-positive strains had higher expression rates for ica operon and sarA genes and lower for the repressor of ica cluster gene (icaR). In order to investigate the interaction of bacteria with the surfaces after attachment, dynamic experiments were performed under two flow conditions. Two different surfaces were used, a modified and a non-modified glass surface. Bacterial adhesion, as well as biofilm production and biofilm formation, was much higher on the modified surface than on the non-modified one for four S. epidermidis strains. This was in agreement with icaA and icaD gene expression that showed increased expression by RT-PCR, for the bacteria adhered at the modified substrate, especially under the high shear rate. Therefore, the combined effect of surface chemistry and shear significantly influence the adhesion of interacting bacterial cells. This indicates that analysis of gene expression not only can greatly refine our knowledge of bacterial-material interactions, but also yield novel biomarkers for potential use in biocompatibility assessment.