Quantitative analysis of adhesion and biofilm formation on hydrophilic and hydrophobic surfaces of clinical isolates of Staphylococcus epidermidis

Subnanometric Roughness Affects the Deposition and Mobile Adhesion of Escherichia coli on Silanized Glass Surfaces

We investigate the deposition and transient adhesion of Escherichia coli on alkyl and fluoroalkyl silanized glass surfaces of different carbon chain lengths. The rate at which bacteria deposit onto these surfaces decreases as the shear stress is increased from 3 to 67 mPa, but trends in the deposition rate across all surfaces cannot be predicted from extended DLVO calculations of the interaction potential. As the surface root-mean-square (rms) roughness increases, the deposition rate increases and the percentage of motile tethered cells decreases. Furthermore, on surfaces of root-mean-square roughness of less than 0.2 nm, bacteria exhibit mobile adhesion, for which surface-associated cells linearly translate distances greater than approximately 1.5 times their average body length along the flow direction. E. coli bacteria with and without flagella exhibit mobile adhesion, indicating that this behavior is not driven by these appendages. Cells that express fimbriae do not exhibit mobile adhesion. These results suggest that even subnanoscale roughness can influence the deposition and transient adhesion of bacteria and imply that strategies to reduce frictional interactions by making cells or surfaces smoother may help to control the initial fouling of surfaces by E. coli bacteria.

Characterizing the in vitro biofilm phenotype of Staphylococcus epidermidis isolates from central venous catheters

Central venous catheter (CVC)-related infections are commonly caused by Staphylococcus epidermidis that is able to form a biofilm on the catheter surface. Many studies involving biofilm formation by Staphylococcus have been published each adopting an own in vitro model. Since the capacity to form a biofilm depends on multiple environmental factors, direct comparison of results obtained in different studies remains challenging. This study characterized the phenotype (strong versus weak biofilm-producers) of S. epidermidis from CVCs in four different in vitro biofilm models, covering differences in material type (glass versus polymer) and nutrient presentation (static versus continuous flow). A good correlation in phenotype was obtained between glass and polymeric surfaces independent of nutrient flow, with 85% correspondence under static growth conditions and 80% under dynamic conditions. A 80% correspondence between static and dynamic conditions on polymeric surfaces could be demonstrated as well. Incubation time had a significant influence on the biofilm phenotype with only 55% correspondence between the dynamic models at different incubation times (48h versus 17h). Screening for the presence of biofilm-related genes only revealed that ica A was correlated with biofilm formation under static but not under dynamic conditions. In conclusion, this study highlights that a high level of standardization is necessary to interpret and compare results of different in vitro biofilm models.

Characterization of an in vitro fed-batch model to obtain cells released from S. epidermidis biofilms

Both dynamic and fed-batch systems have been used for the study of biofilms. Dynamic systems, whose hallmark is the presence of continuous flow, have been considered the most appropriate for the study of the last stage of the biofilm lifecycle: biofilm disassembly. However, fed-batch is still the most used system in the biofilm research field. Hence, we have used a fed-batch system to collect cells released from Staphylococcus epidermidis biofilms, one of the most important etiological agents of medical device-associated biofilm infections. Herein, we showed that using this model it was possible to collect cells released from biofilms formed by 12 different S. epidermidis clinical and commensal isolates. In addition, our data indicated that biofilm disassembly occurred by both passive and active mechanisms, although the last occurred to a lesser extent. Moreover, it was observed that S. epidermidis biofilm-released cells presented higher tolerance to vancomycin and tetracycline, as well as a particular gene expression phenotype when compared with either biofilm or planktonic cells. Using this model, biofilm-released cells phenotype and their interaction with the host immune system could be studied in more detail, which could help providing significant insights into the pathophysiology of biofilm-related infections.

Biofilm formation of Brazilian meticillin-resistant Staphylococcus aureus strains: prevalence of biofilm determinants and clonal profiles

Biofilms plays an important role in medical-device-related infections. This study aimed to determine the factors that influence adherence and biofilm production, as well as the relationship between strong biofilm production and genetic determinants in clinical isolates of meticillin-resistant Staphylococcus aureus (MRSA). Fifteen strains carrying different chromosomal cassettes recovered from hospitalized patients were selected; five SCCmecII, five SCCmecIII and five SCCmecIV. The SCCmec type, agr group and the presence of the virulence genes (bbp, clfA, icaA, icaD, fnbB, bap, sasC and IS256) were assessed by PCR. PFGE and multilocus sequence typing (MLST) techniques were also performed. The initial adhesion and biofilm formation were examined by quantitative assays. The surface tension and hydrophobicity of the strains were measured by the contact angle technique to evaluate the association between these parameters and adhesion ability. SCCmecIII and IV strains were less hydrophilic, with a high value for the electron acceptor parameter and higher adhesion in comparison with SCCmecII strains. Only SCCmecIII strains could be characterized as strong biofilm producers. The PFGE showed five major pulsotypes (A-E); however, biofilm production was related to the dissemination of one specific PFGE clone (C) belonging to MLST ST239 (Brazilian epidemic clonal complex). The genes agrI, fnbB and IS256 in SCCmecIII strains were considered as genetic determinants associated with strong biofilm-formation by an ica-independent biofilm pathway. This study contributes to the understanding of biofilm production as an aggravating factor potentially involved in the persistence and severity of infections caused by multidrug-resistant MRSA belonging to this genotype.

Modulation of Biofilm Exopolysaccharides by the Streptococcus mutans vicX Gene

The cariogenic pathogen Streptococcus mutans effectively utilizes dietary sucrose for the synthesis of exopolysaccharide, which act as a scaffold for its biofilm, thus contributing to its pathogenicity, environmental stress tolerance, and antimicrobial resistance. The two-component system VicRK of S. mutans regulates a group of virulence genes that are associated with biofilm matrix synthesis. Knockout of vicX affects biofilm formation, oxidative stress tolerance, and transformation of S. mutans. However, little is known regarding the vicX-modulated structural characteristics of the exopolysaccharides underlying the biofilm formation and the phenotypes of the vicX mutants. Here, we identified the role of vicX in the structural characteristics of the exopolysaccharide matrix and biofilm physiology. The vicX mutant (SmuvicX) biofilms seemingly exhibited "desertification" with architecturally impaired exopolysaccharide-enmeshed cell clusters, compared with the UA159 strain (S. mutans wild type strain). Concomitantly, SmuvicX showed a decrease in water-insoluble glucan (WIG) synthesis and in WIG/water-soluble glucan (WSG) ratio. Gel permeation chromatography (GPC) showed that the WIG isolated from the SmuvicX biofilms had a much lower molecular weight compared with the UA159 strain indicating differences in polysaccharide chain lengths. A monosaccharide composition analysis demonstrated the importance of the vicX gene in the glucose metabolism. We performed metabolite profiling via (1)H nuclear magnetic resonance spectroscopy, which showed that several chemical shifts were absent in both WSG and WIG of SmuvicX biofilms compared with the UA159 strain. Thus, the modulation of structural characteristics of exopolysaccharide by vicX provides new insights into the interaction between the exopolysaccharide structure, gene functions, and cariogenicity. Our results suggest that vicX gene modulates the structural characteristics of exopolysaccharide associated with cariogenicity, which may be explored as a potential target that contributes to dental caries management. Furthermore, the methods used to purify the EPS of S. mutans biofilms and to analyze multiple aspects of its structure (GPC, gas chromatography-mass spectrometry, and (1)H nuclear magnetic resonance spectroscopy) may be useful approaches to determine the roles of other virulence genes for dental caries prevention.

Sensitivity of antibiotic resistant and antibiotic susceptible Escherichia coli, Enterococcus and Staphylococcus strains against ozone

Tolerance of antibiotic susceptible and antibiotic resistant Escherichia coli, Enterococcus and Staphylococcus strains from clinical and wastewater samples against ozone was tested to investigate if ozone, a strong oxidant applied for advanced wastewater treatment, will affect the release of antibiotic resistant bacteria into the aquatic environment. For this purpose, the resistance pattern against antibiotics of the mentioned isolates and their survival after exposure to 4 mg/L ozone was determined. Antibiotic resistance (AR) of the isolates was not correlating with higher tolerance against ozone. Except for ampicillin resistant E. coli strains, which showed a trend towards increased resistance, E. coli strains that were also resistant against cotrimoxazol, ciprofloxacin or a combination of the three antibiotics were similarly or less resistant against ozone than antibiotic sensitive strains. Pigment-producing Enterococcus casseliflavus and Staphylococcus aureus seemed to be more resistant against ozone than non-pigmented species of these genera. Furthermore, aggregation or biofilm formation apparently protected bacteria in subsurface layers from inactivation by ozone. The relatively large variance of tolerance against ozone may indicate that resistance to ozone inactivation most probably depends on several factors, where AR, if at all, does not play a major role.

Optimization of culture conditions for Gardnerella vaginalis biofilm formation

Bacterial vaginosis is the leading vaginal disorder in women in reproductive age. Although bacterial vaginosis is related with presence of a biofilm composed predominantly by Gardnerella vaginalis, there has not been a detailed information addressing the environmental conditions that influence the biofilm formation of this bacterial species. Here, we evaluated the influence of some common culture conditions on G. vaginalis biofilm formation, namely inoculum concentration, incubation period, feeding conditions and culture medium composition. Our results showed that culture conditions strongly influenced G. vaginalis biofilm formation and that biofilm formation was enhanced when starting the culture with a higher inoculum, using a fed-batch system and supplementing the growth medium with maltose.

Effect of UV-photofunctionalization on oral bacterial attachment and biofilm formation to titanium implant material

Bacterial biofilm infections remain prevalent reasons for implant failure. Dental implant placement occurs in the oral environment, which harbors a plethora of biofilm-forming bacteria. Due to its trans-mucosal placement, part of the implant structure is exposed to oral cavity and there is no effective measure to prevent bacterial attachment to implant materials. Here, we demonstrated that UV treatment of titanium immediately prior to use (photofunctionalization) affects the ability of human polymicrobial oral biofilm communities to colonize in the presence of salivary and blood components. UV-treatment of machined titanium transformed the surface from hydrophobic to superhydrophilic. UV-treated surfaces exhibited a significant reduction in bacterial attachment as well as subsequent biofilm formation compared to untreated ones, even though overall bacterial viability was not affected. The function of reducing bacterial colonization was maintained on UV-treated titanium that had been stored in a liquid environment before use. Denaturing gradient gel-electrophoresis (DGGE) and DNA sequencing analyses revealed that while bacterial community profiles appeared different between UV-treated and untreated titanium in the initial attachment phase, this difference vanished as biofilm formation progressed. Our findings confirm that UV-photofunctionalization of titanium has a strong potential to improve outcome of implant placement by creating and maintaining antimicrobial surfaces.

Using an in-vitro biofilm model to assess the virulence potential of bacterial vaginosis or non-bacterial vaginosis Gardnerella vaginalis isolates

Gardnerella vaginalis is the most common species found in bacterial vaginosis (BV). However, it is also present in a significant proportion of healthy women and G. vaginalis vaginal colonization does not always lead to BV. In an effort to better understand the differences between G. vaginalis isolated from women with a positive (BV) versus a negative (non-BV) diagnosis of BV, we compared the virulence potential of 7 BV and 7 non-BV G. vaginalis isolates and assessed the virulence factors related to biofilm formation, namely: initial adhesion and cytotoxic effect, biofilm accumulation, susceptibility to antibiotics, and transcript levels of the known vaginolysin, and sialidase genes. Furthermore, we also determined the ability of G. vaginalis to displace lactobacilli previously adhered to HeLa cells. Our results showed that non-BV strains were less virulent than BV strains, as suggested by the lower cytotoxicity and initial adhesion to Hela cells. Significant differences in expression of known virulence genes were also detected, further suggesting a higher virulence potential of the BV associated G. vaginalis. Importantly, we demonstrated that BV associated G. vaginalis were able to displace pre-coated vaginal protective lactobacilli and we hypothesize this to be a trigger for BV development.

Silver activation on thin films of Ag-ZrCN coatings for antimicrobial activity

Nowadays, with the increase of elderly population and related health problems, knee and hip joint prosthesis are being widely used worldwide. However, failure of these invasive devices occurs in a high percentage thus demanding the revision of the chirurgical procedure. Within the reasons of failure, microbial infections, either hospital or subsequently-acquired, contribute in high number to the statistics. Staphylococcus epidermidis (S. epidermidis) has emerged as one of the major nosocomial pathogens associated with these infections. Silver has a historic performance in medicine due to its potent antimicrobial activity, with a broad-spectrum on the activity of different types of microorganisms. Consequently, the main goal of this work was to produce Ag-ZrCN coatings with antimicrobial activity, for the surface modification of hip prostheses. Thin films of ZrCN with several silver concentrations were deposited onto stainless steel 316 L, by DC reactive magnetron sputtering, using two targets, Zr and Zr with silver pellets (Zr+Ag target), in an atmosphere containing Ar, C2H2 and N2. The antimicrobial activity of the modified surfaces was tested against S. epidermidis and the influence of an activation step of silver was assessed by testing samples after immersion in a 5% (w/v) NaClO solution for 5 min. The activation procedure revealed to be essential for the antimicrobial activity, as observed by the presence of an inhibition halo on the surface with 11 at.% of Ag. The morphology analysis of the surface before and after the activation procedure revealed differences in silver distribution indicating segregation/diffusion of the metallic element to the film's surface. Thus, the results indicate that the silver activation step is responsible for an antimicrobial effect of the coatings, due to silver oxidation and silver ion release.

Surfaces Presenting α-Phenyl Mannoside Derivatives Enable Formation of Stable, High Coverage, Non-pathogenic Escherichia coli Biofilms against Pathogen Colonization

Prevention of pathogenic colonization on medical devices over a long period of time remains a great challenge, especially in a high-nutrient environment that accelerates production of biomass leading to biofouling of the device. Since biofouling and the subsequent pathogen colonization is eventually inevitable, a new strategy using non-pathogenic bacteria as living guards against pathogenic colonization on medical devices has attracted increasing interest. Crucial to the success of this strategy is to pre-establish a high coverage and stable biofilm of benign bacteria on the surface. Silicone elastomers are one of the most widely used materials in biomedical devices. In this work, we modified silicone surfaces to promote formation of high coverage and stable biofilms by a non-pathogenic Escherichia coli strain 83972 with type 1 fimbriae (fim+) to interfere the colonization of an aggressive biofilm-forming, uropathogenic Enterococcus faecalis. Although it is well known that mannoside surfaces promote the initial adherence of fim+ E. coli through binding to the FimH receptor at the tip of the type 1 fimbriae, it is not clear whether the fast initial adherence could lead to a high coverage and stable protective biofilm. To explore the role of mannoside ligands, we synthesized a series of alkyl and aryl mannosides varied in structure and immobilized them on silicone surfaces pre-coated with poly(amidoamine) (PAMAM) dendrimer. We found that stable and densely packed benign E. coli biofilms were formed on the surfaces presenting biphenyl mannoside with the highest initial adherence of fim+ E. coli. These non-pathogenic biofilms prevented the colonization of E. faecalis for 11 days at a high concentration (108 CFU mL-1, 100,000 times above the diagnostic threshold for urinary tract infection) in the nutrient-rich Lysogeny Broth (LB) media. The result shows a correlation among the initial adherence of fim+ E. coli 83972, the coverage and long-term stability of the resultant biofilms, as well as their efficiency for preventing the pathogen colonization.

Evaluating the Effect of Copper Nanoparticles in Inhibiting Pseudomonas aeruginosa and Listeria monocytogenes Biofilm Formation

Background:

Biofilm formation is a major virulence factor in different bacteria. Biofilms allow bacteria to resist treatment with antibacterial agents. The biofilm formation on glass and steel surfaces, which are extremely useful surfaces in food industries and medical devices, has always had an important role in the distribution and transmission of infectious diseases.

Objectives:

In this study, the effect of coating glass and steel surfaces by copper nanoparticles (CuNPs) in inhibiting the biofilm formation by Listeria monocytogenes and Pseudomonas aeruginosa was examined.

Materials and Methods:

The minimal inhibitory concentrations (MICs) of synthesized CuNPs were measured against L. monocytogenes and P. aeruginosa by using the broth-dilution method. The cell-surface hydrophobicity of the selected bacteria was assessed using the bacterial adhesion to hydrocarbon (BATH) method. Also, the effect of the CuNP-coated surfaces on the biofilm formation of the selected bacteria was calculated via the surface assay.

Results:

The MICs for the CuNPs according to the broth-dilution method were ≤ 16 mg/L for L. monocytogenes and ≤ 32 mg/L for P. aeruginosa. The hydrophobicity of P. aeruginosa and L. monocytogenes was calculated as 74% and 67%, respectively. The results for the surface assay showed a significant decrease in bacterial attachment and colonization on the CuNP-covered surfaces.

Conclusions:

Our data demonstrated that the CuNPs inhibited bacterial growth and that the CuNP-coated surfaces decreased the microbial count and the microbial biofilm formation. Such CuNP-coated surfaces can be used in medical devices and food industries, although further studies in order to measure their level of toxicity would be necessary.

Fabrication of a platform to isolate the influences of surface nanotopography from chemistry on bacterial attachment and growth

Billions of dollars are spent annually worldwide to combat the adverse effects of bacterial attachment and biofilm formation in industries as varied as maritime, food, and health. While advances in the fabrication of antifouling surfaces have been reported recently, a number of the essential aspects responsible for the formation of biofilms remain unresolved, including the important initial stages of bacterial attachment to a substrate surface. The reduction of bacterial attachment to surfaces is a key concept in the prevention or minimization of biofilm formation. The chemical and physical characteristics of both the substrate and bacteria are important in understanding the attachment process, but substrate modification is likely the most practical route to enable the extent of bacterial attachment taking place to be effectively controlled. The microtopography and chemistry of the surface are known to influence bacterial attachment. The role of surface chemistry versus nanotopography and their interplay, however, remain unclear. Most methods used for imparting nanotopographical patterns onto a surface also induce changes in the surface chemistry and vice versa. In this study, the authors combine colloidal lithography and plasma polymerization to fabricate homogeneous, reproducible, and periodic nanotopographies with a controllable surface chemistry. The attachment of Escherichia coli bacteria onto carboxyl (plasma polymerized acrylic acid, ppAAc) and hydrocarbon (plasma polymerized octadiene, ppOct) rich plasma polymer films on either flat or colloidal array surfaces revealed that the surface chemistry plays a critical role in bacterial attachment, whereas the effect of surface nanotopography on the bacterial attachment appears to be more difficult to define. This platform represents a promising approach to allow a greater understanding of the role that surface chemistry and nanotopography play on bacterial attachment and the subsequent biofouling of the surface.

Self-assembled capsules of poly-N-glycidyl histidine ether–tannic acid for inhibition of biofilm formation in urinary catheters

A coating made of N-glycidyl-histidine ether–tannic acid complex, a biocompatible polymer, onto a catheter surface inhibits the biofilm formation and helps to control the catheter associated infections caused by biofilm forming MDR pathogens.

Impact of confining 3-D polymer networks on dynamics of bacterial ingress and self-organisation

Alignment of microbial colonies along with polymeric cell wall.

Biocompatible succinic acid-based polyesters for potential biomedical applications: fungal biofilm inhibition and mesenchymal stem cell growth

Poly(alkene succinates) are promising materials for specialized medical devices and tissue engineering, presenting intrinsic properties, such as; fungal biofilm inhibition, biocompatibility and stem cells controlled growth promotion.

Methodological approaches for studying the microbial ecology of drinking water distribution systems

The study of the microbial ecology of drinking water distribution systems (DWDS) has traditionally been based on culturing organisms from bulk water samples. The development and application of molecular methods has supplied new tools for examining the microbial diversity and activity of environmental samples, yielding new insights into the microbial community and its diversity within these engineered ecosystems. In this review, the currently available methods and emerging approaches for characterising microbial communities, including both planktonic and biofilm ways of life, are critically evaluated. The study of biofilms is considered particularly important as it plays a critical role in the processes and interactions occurring at the pipe wall and bulk water interface. The advantages, limitations and usefulness of methods that can be used to detect and assess microbial abundance, community composition and function are discussed in a DWDS context. This review will assist hydraulic engineers and microbial ecologists in choosing the most appropriate tools to assess drinking water microbiology and related aspects.

Early staphylococcal biofilm formation on solid orthopaedic implant materials: in vitro study

Biofilms forming on the surface of biomaterials can cause intractable implant-related infections. Bacterial adherence and early biofilm formation are influenced by the type of biomaterial used and the physical characteristics of implant surface. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis, the main pathogen in implant-related infections, to form biofilms on the surface of the solid orthopaedic biomaterials, oxidized zirconium-niobium alloy, cobalt-chromium-molybdenum alloy (Co-Cr-Mo), titanium alloy (Ti-6Al-4V), commercially pure titanium (cp-Ti) and stainless steel. A bacterial suspension of Staphylococcus epidermidis strain RP62A (ATCC35984) was added to the surface of specimens and incubated. The stained biofilms were imaged with a digital optical microscope and the biofilm coverage rate (BCR) was calculated. The total amount of biofilm was determined with the crystal violet assay and the number of viable cells in the biofilm was counted using the plate count method. The BCR of all the biomaterials rose in proportion to culture duration. After culturing for 2-4 hours, the BCR was similar for all materials. However, after culturing for 6 hours, the BCR for Co-Cr-Mo alloy was significantly lower than for Ti-6Al-4V, cp-Ti and stainless steel (P<0.05). The absorbance value determined in the crystal violet assay and the number of viable cells on Co-Cr-Mo were not significantly lower than for the other materials (P>0.05). These results suggest that surface properties, such as hydrophobicity or the low surface free energy of Co-Cr-Mo, may have some influence in inhibiting or delaying the two-dimensional expansion of biofilm on surfaces with a similar degree of smoothness.

Attachment from flow of Escherichia coli bacteria onto silanized glass substrates

We investigate the attachment of Escherichia coli on silanized glass surfaces during flow through a linear channel at flow rates of 0.1-1 mL/min using confocal microscopy. We assemble layers of organosilanes on glass and track the position and orientation of bacteria deposited on these surfaces during flow with high spatial resolution. We find that a metric based on the degree of the surface-tethered motion of bacteria driven by flagella is inversely correlated with deposition rate, whereas conventional surface characterizations, such as surface energy or water contact angle, are uncorrelated. Furthermore, the likelihood that an initially moving bacterium becomes immobilized increases with increasing deposition rate. Our results suggest that the chemistry and arrangement of silane molecules on the surface influence the transition from transient to irreversible attachment by favoring different mechanisms used by bacteria to attach to surfaces.

Increased biofilm formation by nontypeable Haemophilus influenzae isolates from patients with invasive disease or otitis media versus strains recovered from cases of respiratory infections

Biofilm formation by nontypeable (NT) Haemophilus influenzae remains a controversial topic. Nevertheless, biofilm-like structures have been observed in the middle-ear mucosa of experimental chinchilla models of otitis media (OM). To date, there have been no studies of biofilm formation in large collections of clinical isolates. This study aimed to investigate the initial adhesion to a solid surface and biofilm formation by NT H. influenzae by comparing isolates from healthy carriers, those with noninvasive respiratory disease, and those with invasive respiratory disease. We used 352 isolates from patients with nonbacteremic community-acquired pneumonia (NB-CAP), chronic obstructive pulmonary disease (COPD), OM, and invasive disease and a group of healthy colonized children. We then determined the speed of initial adhesion to a solid surface by the BioFilm ring test and quantified biofilm formation by crystal violet staining. Isolates from different clinical sources displayed high levels of biofilm formation on a static solid support after growth for 24 h. We observed clear differences in initial attachment and biofilm formation depending on the pathology associated with NT H. influenzae isolation, with significantly increased biofilm formation for NT H. influenzae isolates collected from patients with invasive disease and OM compared with NT H. influenzae isolates from patients with NB-CAP or COPD and healthy colonized subjects. In all cases, biofilm structures were detached by proteinase K treatment, suggesting an important role for proteins in the initial adhesion and static biofilm formation measured by crystal violet staining.

How microorganisms use hydrophobicity and what does this mean for human needs?

Cell surface hydrophobicity (CSH) plays a crucial role in the attachment to, or detachment from the surfaces. The influence of CSH on adhesion of microorganisms to biotic and abiotic surfaces in medicine as well as in bioremediation and fermentation industry has both negative and positive aspects. Hydrophobic microorganisms cause the damage of surfaces by biofilm formation; on the other hand, they can readily accumulate on organic pollutants and decompose them. Hydrophilic microorganisms also play a considerable role in removing organic wastes from the environment because of their high resistance to hydrophobic chemicals. Despite the many studies on the environmental and metabolic factors affecting CSH, the knowledge of this subject is still scanty and is in most cases limited to observing the impact of hydrophobicity on adhesion, aggregation or flocculation. The future of research seems to lie in finding a way to managing the microbial adhesion process, perhaps by steering cell hydrophobicity.

Methylobacterium populi VP2: plant growth-promoting bacterium isolated from a highly polluted environment for polycyclic aromatic hydrocarbon (PAH) biodegradation

The use of microorganisms to accelerate the natural detoxification processes of toxic substances in the soil represents an alternative ecofriendly and low-cost method of environmental remediation compared to harmful incineration and chemical treatments. Fourteen strains able to grow on minimal selective medium with a complex mixture of different classes of xenobiotic compounds as the sole carbon source were isolated from the soil of the ex-industrial site ACNA (Aziende Chimiche Nazionali Associate) in Cengio (Savona, Italy). The best putative degrading isolate, Methylobacterium populi VP2, was identified using a polyphasic approach on the basis of its phenotypic, biochemical, and molecular characterisation. Moreover, this strain also showed multiple plant growth promotion activities: it was able to produce indole-3-acetic acid (IAA) and siderophores, solubilise phosphate, and produce a biofilm in the presence of phenanthrene and alleviate phenanthrene stress in tomato seeds. This is the first report on the simultaneous occurrence of the PAH-degrading ability by Methylobacterium populi and its multiple plant growth-promoting activities. Therefore, the selected indigenous strain, which is naturally present in highly contaminated soils, is good candidate for plant growth promotion and is capable of biodegrading xenobiotic organic compounds to remediate contaminated soil alone and/or soil associated with plants.

Escherichia coli adhesion, biofilm development and antibiotic susceptibility on biomedical materials

The aim of this work was to test materials typically used in the construction of medical devices regarding their influence in the initial adhesion, biofilm development and antibiotic susceptibility of Escherichia coli biofilms. Adhesion and biofilm development was monitored in 12-well microtiter plates containing coupons of different biomedical materials--silicone (SIL), stainless steel (SS) and polyvinyl chloride (PVC)--and glass (GLA) as control. The susceptibility of biofilms to ciprofloxacin and ampicillin was assessed, and the antibiotic effect in cell morphology was observed by scanning electron microscopy. The surface hydrophobicity of the bacterial strain and materials was also evaluated from contact angle measurements. Surface hydrophobicity was related with initial E. coli adhesion and subsequent biofilm development. Hydrophobic materials, such as SIL, SS, and PVC, showed higher bacterial colonization than the hydrophilic GLA. Silicone was the surface with the greatest number of adhered cells and the biofilms formed on this material were also less susceptible to both antibiotics. It was found that different antibiotics induced different levels of elongation on E. coli sessile cells. Results revealed that, by affecting the initial adhesion, the surface properties of a given material can modulate biofilm buildup and interfere with the outcome of antimicrobial therapy. These findings raise the possibility of fine-tuning surface properties as a strategy to reach higher therapeutic efficacy.

Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties

Surface modification and providing antibacterial properties to the materials or devices are getting great attention especially in the last decades. In this study, polyurethane (PU) films were prepared by synthesizing them in medical purity from toluene diisocyanate and polypropylene ethylene glycol without using any other ingredients and then the film surfaces were modified by covalent immobilization of chitosan (CH) which has antibacterial activity. CH immobilized PU films (PU-CH) were found to be more hydrophilic than control PU films. Electron Spectroscopy for Chemical Analysis (ESCA) and Atomic Force Microscopy (AFM) analyses showed higher nitrogen contents and rougher surface topography for PU-CH compared to PU films. Modification with CH significantly increased antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) bacteria. It was observed that the number of bacteria colonies were less about 10(2)-10(5) CFU/mL and number of attached viable bacteria decreased significantly after CH modification of PU films.

Biofilm formation and persistence on abiotic surfaces in the context of food and medical environments

The biofilm formation on abiotic surfaces in food and medical sectors constitutes a great public health concerns. In fact, biofilms present a persistent source for pathogens, such as Pseudomonas aeruginosa and Staphylococcus aureus, which lead to severe infections such as foodborne and nosocomial infections. Such biofilms are also a source of material deterioration and failure. The environmental conditions, commonly met in food and medical area, seem also to enhance the biofilm formation and their resistance to disinfectant agents. In this regard, this review highlights the effect of environmental conditions on bacterial adhesion and biofilm formation on abiotic surfaces in the context of food and medical environment. It also describes the current and emergent strategies used to study the biofilm formation and its eradication. The mechanisms of biofilm resistance to commercialized disinfectants are also discussed, since this phenomenon remains unclear to date.

Exposure of Escherichia coli ATCC 12806 to sublethal concentrations of food-grade biocides influences its ability to form biofilm, resistance to antimicrobials, and ultrastructure

Escherichia coli ATCC 12806 was exposed to increasing subinhibitory concentrations of three biocides widely used in food industry facilities: trisodium phosphate (TSP), sodium nitrite (SNI), and sodium hypochlorite (SHY). The cultures exhibited an acquired tolerance to biocides (especially to SNI and SHY) after exposure to such compounds. E. coli produced biofilms (as observed by confocal laser scanning microscopy) on polystyrene microtiter plates. Previous adaptation to SNI or SHY enhanced the formation of biofilms (with an increase in biovolume and surface coverage) both in the absence and in the presence (MIC/2) of such compounds. TSP reduced the ability of E. coli to produce biofilms. The concentration of suspended cells in the culture broth in contact with the polystyrene surfaces did not influence the biofilm structure. The increase in cell surface hydrophobicity (assessed by a test of microbial adhesion to solvents) after contact with SNI or SHY appeared to be associated with a strong capacity to form biofilms. Cultures exposed to biocides displayed a stable reduced susceptibility to a range of antibiotics (mainly aminoglycosides, cephalosporins, and quinolones) compared with cultures that were not exposed. SNI caused the greatest increase in resistances (14 antibiotics [48.3% of the total tested]) compared with TSP (1 antibiotic [3.4%]) and SHY (3 antibiotics [10.3%]). Adaptation to SHY involved changes in cell morphology (as observed by scanning electron microscopy) and ultrastructure (as observed by transmission electron microscopy) which allowed this bacterium to persist in the presence of severe SHY challenges. The findings of the present study suggest that the use of biocides at subinhibitory concentrations could represent a public health risk.

Antibacterial activity studies of plasma polymerised cineole films

Costs associated with bacterial infections in medical devices exceed $US 30 billion each year in the United States alone due to device revisions and patient treatment.

Low metabolic activity of biofilm formed by Enterococcus faecalis isolated from healthy humans and wild mallards (Anas platyrhynchos)

It is widely known that Enterococcus faecalis virulence is related to its biofilm formation. Although Enterococci are common commensal organisms of the gastrointestinal tract, the difference between commensal and pathogen strains remain unclear. In this study, we compare the biochemical profile of the biofilms formed by two groups of medical and two groups of commensal strains. The medical strains were isolated as pathogens from infections of urinary tract and other infections (wounds, pus and bedsores), and the commensal strains were taken from faeces of healthy volunteers and faeces of wild mallards (Anas platyrhynchos) living in an urban environment. The properties of biofilms formed by medical and commensal strains differed significantly. Commensal strains showed lower metabolic activity and glucose uptake and higher biofilm biomass than the medical ones. Consistent with glucose uptake experiments, we found that the glucose dehydrogenase gene was more expressed in medical strains. These results indicate that higher metabolic activity and lower protein concentration of E. faecalis cells within biofilms are formed during infections.

Influence of nanohydroxyapatite surface properties on Staphylococcus epidermidis biofilm formation

Nanohydroxyapatite (nanoHA), due to its chemical properties, has appeared as an exceptionally promising bioceramic to be used as bone regeneration material. Staphylococcus epidermidis have emerged as major nosocomial pathogens associated with infections of implanted medical devices. In this work, the purpose was to study the influence of the nanoHA surface characteristics on S. epidermidis RP62A biofilm formation. Therefore, two different initial inoculum concentrations (Ci) were used in order to check if these would affect the biofilm formed on the nanoHA surfaces. Biofilm formation was followed by the enumeration of cultivable cells and by scanning electron microscopy. Surface topography, contact angle, total surface area and porosimetry of the biomaterials were studied and correlated with the biofilm data. The surface of nanoHA sintered at 830℃ (nanoHA830) showed to be more resistant to S. epidermidis attachment and accumulation than that of nanoHA sintered at 1000℃ (nanoHA1000). The biofilm formed on nanoHA830 presented differences in terms of structure, surface coverage and EPS production when compared to the one formed on nanoHA1000 surface. It was observed that topography and surface area of nanoHA surfaces had influence on the bacterial attachment and accumulation. Ci influenced bacteria attachment and accumulation on nanoHA surfaces over time. The choice of the initial inoculum concentration was relevant proving to have an effect on the extent of adherence thus being a critical point for human health if these materials are used in implantable devices. This study showed that the initial inoculum concentration and surface material properties determine the rate of microbial attachment to substrata and consequently are related to biofilm-associated infections in biomaterials.

Current and emerging environmentally-friendly systems for fouling control in the marine environment

Following the ban in 2003 on the use of tributyl-tin compounds in antifouling coatings, the search for an environmentally-friendly alternative has accelerated. Biocidal TBT alternatives, such as diuron and Irgarol 1051®, have proved to be environmentally damaging to marine organisms. The issue regarding the use of biocides is that concerning the half-life of the compounds which allow a perpetuation of the toxic effects into the marine food chain, and initiate changes in the early stages of the organisms' life-cycle. In addition, the break-down of biocides can result in metabolites with greater toxicity and longevity than the parent compound. Functionalized coatings have been designed to repel the settlement and permanent attachment of fouling organisms via modification of either or both surface topography and surface chemistry, or by interfering with the natural mechanisms via which fouling organisms settle upon and adhere to surfaces. A large number of technologies are being developed towards producing new coatings that will be able to resist biofouling over a period of years and thus truly replace biocides as antifouling systems. In addition urgent research is directed towards the exploitation of mechanisms used by living organisms designed to repel the settlement of fouling organisms. These biomimetic strategies include the production of antifouling enzymes and novel surface topography that are incompatible with permanent attachment, for example, by mimicking the microstructure of shark skin. Other research seeks to exploit chemical signals and antimicrobial agents produced by diverse living organisms in the environment to prevent settlement and growth of fouling organisms on vulnerable surfaces. Novel polymer-based technologies may prevent fouling by means of unfavourable surface chemical and physical properties or by concentrating antifouling compounds around surfaces.

Interactions between Lactobacillus crispatus and bacterial vaginosis (BV)-associated bacterial species in initial attachment and biofilm formation

Certain anaerobic bacterial species tend to predominate the vaginal flora during bacterial vaginosis (BV), with Gardnerella vaginalis being the most common. However, the exact role of G. vaginalis in BV has not yet been determined. The main goal of this study was to test the hypothesis that G. vaginalis is an early colonizer, paving the way for intermediate (e.g., Fusobacterium nucleatum) and late colonizers (e.g., Prevotella bivia). Theoretically, in order to function as an early colonizer, species would need to be able to adhere to vaginal epithelium, even in the presence of vaginal lactobacilli. Therefore, we quantified adherence of G. vaginalis and other BV-associated bacteria to an inert surface pre-coated with Lactobacillus crispatus using a new Peptide Nucleic Acid (PNA) Fluorescence In Situ Hybridization (FISH) methodology. We found that G. vaginalis had the greatest capacity to adhere in the presence of L. crispatus. Theoretically, an early colonizer would contribute to the adherence and/or growth of additional species, so we next quantified the effect of G. vaginalis biofilms on the adherence and growth of other BV-associated species by quantitative Polymerase Chain Reaction (qPCR) technique. Interestingly, G. vaginalis derived a growth benefit from the addition of a second species, regardless of the species. Conversely, G. vaginalis biofilms enhanced the growth of P. bivia, and to a minor extent of F. nucleatum. These results contribute to our understanding of BV biofilm formation and the progression of the disorder.

Influence of surface features on the adhesion of Staphylococcus epidermidis to Ag-TiCN thin films

Staphylococcus epidermidis has emerged as one of the major nosocomial pathogens associated with infections of implanted medical devices. The initial adhesion of these organisms to the surface of biomaterials is assumed to be an important stage in their colonization. The main objective of this work is to assess the influence of surface features on the adhesion of S. epidermidis to Ag-TiCN coatings deposited by dc reactive magnetron sputtering. The structural results obtained by x-ray diffraction show that the coatings crystallize in a B1-NaCl crystal structure typical of TiC0.3N0.7. The increase of Ag content promoted the formation of Ag crystalline phases. According to the results obtained with atomic force microscopy, a decrease on the surface roughness of the films from 39 to 7 nm is observed as the Ag content increases from 0 to 15 at.%. Surface energy results show that the increase of Ag promotes an increase in hydrophobicity. Bacterial adhesion and biofilm formation on coatings were assessed by the enumeration of the number of viable cells. The results showed that the surface with lower roughness and higher hydrophobicity leads to greater bacterial adhesion and biofilm formation, highlighting that surface morphology and hydrophobicity rule the colonization of materials.

Optimization of an automatic counting system for the quantification of Staphylococcus epidermidis cells in biofilms

Biofilm formation is recognized as the main virulence factor in a variety of chronic infections. In vitro evaluation of biofilm formation is often achieved by quantification of viable or total cells. However, these methods depend on biofilm disruption, which is often achieved by vortexing or sonication. In this study, we investigated the effects of sonication on the elimination of Staphylococcus epidermidis cell clusters from biofilms grown over time, and quantification was performed by three distinct analytical techniques. Even when a higher number of sonication cycles was used, some stable cell clusters remained in the samples obtained from 48- and 72-h-old biofilms, interfering with the quantification of sessile bacteria by plate counting. On the other hand, the fluorescence microscopy automatic counting system allowed proper quantification of biofilm samples that had undergone any of the described sonication cycles, suggesting that this is a more accurate method for assessing the cell concentration in S. epidermidis biofilms, especially in mature biofilms.

Combined effect of linezolid and N-acetylcysteine against Staphylococcus epidermidis biofilms

INTRODUCTION

Staphylococcus epidermidis is an organism commonly associated with infections caused by biofilms. Biofilms are less sensible to antibiotics and therefore are more difficult to eradicate. Linezolid and N-acetylcysteine (NAC), have demonstrated to be active against gram-positive microorganisms. Therefore and since linezolid and NAC have different modes of action, the main objective of this work was to investigate the single and synergistic effect of linezolid and NAC against S. epidermidis biofilms.

METHODS

This work reports the in vitro effect of linezolid and NAC against S. epidermidis biofilms, treated with MIC (4mgml(-1)) and 10×MIC of NAC, and MIC (1μgml(-1)) and peak serum concentration (PS=18μgml(-1)) of linezolid alone and in combination. After exposure of S. epidermidis biofilms to linezolid and/or NAC for 24h, several biofilm parameters were evaluated, namely the number of cultivable cells [colony forming unit (CFU) enumeration], total biofilm biomass and cellular activity.

RESULTS

When tested alone, NAC at 10×MIC was the most effective agent against S. epidermidis biofilms. However, the combination linezolid (MIC)+NAC (10×MIC) showed a synergistic effect and was the most biocidal treatment tested, promoting a 5log reduction in the number of biofilm viable cells.

CONCLUSION

This combination seems to be a potential candidate to combat infections caused by S. epidermidis biofilms, namely as a catheter lock solution therapy.

Farnesol induces cell detachment from established S. epidermidis biofilms

Antibiotic resistance is a serious problem in Staphylococcus epidermidis infections as many clinical isolates of this organism are resistant to up to eight different antibiotics. The increased resistance to conventional antibiotic therapy has lead to the search for new antimicrobial therapeutic agents. Farnesol, an essential oil found in many plants, has been shown to be active against S. epidermidis. Using a type control strain we recently described that although farnesol was not efficient at killing biofilm bacteria, a strong reduction on biofilm biomass was detected, and we hypothesize that farnesol could, somehow, induce biofilm detachment. In this report, to test our hypothesis we used 36 representative clinical strains of S. epidermidis from different geographic locations and characterized them in terms of genetic variability by multilocus sequence typing and staphylococcal chromosome cassette mec. Strains were tested for biofilm formation, and the presence of ica, bhp and aap genes was determined. Stronger biofilms had always the presence of ica operon but often co-harbored bhp and aap genes. Farnesol was then used in biofilm-forming strains, and biofilm detachment was detected in half of the strains tested. Furthermore, we also showed that farnesol inability to kill biofilm bacteria was not the result of the biofilm structure but was related to high cell density. Our results demonstrate, for the first time, that the biomass reduction previously found by us, and many other groups, is the result not of cell killing but instead is the result of biofilm detachment.