Attachment of staphylococci to different plastic tubes in vitro

Structural Diversity in Early-Stage Biofilm Formation on Microplastics Depends on Environmental Medium and Polymer Properties

Plastics entering the environment can not only undergo physical degradation and fragmentation processes, but they also tend to be colonized by microorganisms. Microbial colonization and the subsequent biofilm formation on plastics can alter their palatability to organisms and result in a higher ingestion as compared to pristine plastics. To date, the early stage of biofilm formation on plastic materials has not been investigated in context of the environmental medium and polymer properties. We explored the early-stage biofilm formation on polyamide (PA), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) after incubation in freshwater and artificial seawater and categorized the structural diversity on images obtained via scanning electron microscopy. Furthermore, by the measurement of the initial ζ-potential of the plastic materials, we found that PA with the highest negative ζ-potential tended to have the highest structural diversity, followed by PET and PVC after incubation in freshwater. However, PVC with the lowest negative ζ-potential showed the highest structural diversity after incubation in seawater, indicating that the structural diversity is additionally dependent on the incubation medium. Our results give insights into how the incubation medium and polymer properties can influence the early-stage biofilm formation of just recently environmentally exposed microplastics. These differences are responsible for whether organisms may ingest microplastic particles with their food or not.

Stenosis triggers spread of helical Pseudomonas biofilms in cylindrical flow systems

Biofilms are multicellular bacterial structures that adhere to surfaces and often endow the bacterial population with tolerance to antibiotics and other environmental insults. Biofilms frequently colonize the tubing of medical devices through mechanisms that are poorly understood. Here we studied the helicoidal spread of Pseudomonas putida biofilms through cylindrical conduits of varied diameters in slow laminar flow regimes. Numerical simulations of such flows reveal vortical motion at stenoses and junctions, which enhances bacterial adhesion and fosters formation of filamentous structures. Formation of long, downstream-flowing bacterial threads that stem from narrowings and connections was detected experimentally, as predicted by our model. Accumulation of bacterial biomass makes the resulting filaments undergo a helical instability. These incipient helices then coarsened until constrained by the tubing walls, and spread along the whole tube length without obstructing the flow. A three-dimensional discrete filament model supports this coarsening mechanism and yields simulations of helix dynamics in accordance with our experimental observations. These findings describe an unanticipated mechanism for bacterial spreading in tubing networks which might be involved in some hospital-acquired infections and bacterial contamination of catheters.

Synthesis of biomimetic segmented polyurethanes as antifouling biomaterials

Controlling the non-specific adsorption of proteins, cells and bacteria onto biomaterial surfaces is of crucial importance for the development of medical devices with specific levels of performance. Among the strategies pursued to control the interactions between material surfaces and biological tissues, the immobilization of non-fouling polymers on biomaterial surfaces as well as the synthesis of the so-called biomimetic polymers are considered promising approaches to elicit specific cellular responses. In this study, in order to obtain materials able to prevent infectious and thrombotic complications related to the use of blood-contacting medical devices, heparin-mimetic segmented polyurethanes were synthesized and fully characterized. Specifically, sulfate or sulfamate groups, known to be responsible for the biological activity of heparin, were introduced into the side chain of a carboxylated polyurethane. Due to the introduction of these groups, the obtained polymers possessed a higher hard/soft phase segregation (lower glass transition temperatures) and a greater hydrophilicity than the pristine polymer. In addition, the synthesized polymers were able to significantly delay the activated partial thromboplastin time, this increased hemocompatibility being related both to polymer hydrophilicity and to the presence of the -SO3H groups. This last feature was also responsible for the ability of these biomimetic polymers to prevent the adhesion of a strain of Staphylococcus epidermidis.

Synthesis, characterization, andin vitro activity of antibiotic releasing polyurethanes to prevent bacterial resistance

Central venous catheters are a major cause of nosocomial bloodstream infections. Different attempts have been made to incorporate antimicrobial agents into catheters, particularly directed at the surface-coating of devices. To facilitate the antimicrobial adsorption, various cationic surfactants, which however showed several problems, have been used. On the other hand, impregnated catheters with only antimicrobials have demonstrated a short-term duration due to the difficulties to deliver the drug slowly. Thus, in order to obtain high antimicrobial-polymer affinity we synthesized or modified polyurethanes to introduce different functional groups. Polymers were loaded with two antibiotics, cefamandole nafate and rifampin (RIF), chosen for both their functional groups and their action spectrum. The in vitro release behavior showed that the elution of drugs depended on the matrix hydrophilicity and on the antibiotic-polymer and antibiotic-antibiotic interactions. To increase the amount of drug released, polyethylene glycol (PEG) used as a pore forming agent at different molecular weights was incorporated in the polymer bulk with antibiotics. As for the in vitro antimicrobial activity of matrices, assessed by Kirby-Bauer test, it was seen that antibiotics released from various formulations inhibited the bacterial growth and exerted a synergistic effect when both were present. In particular, PEG10000-containing polymer was active against the RIF-resistant S. aureus strain up to 23 days. These results suggest that the combined entrapping of antibiotics and pore formers in these novel polymer systems could be promising to prevent the bacterial colonization and to control the emergence of bacterial resistance.

Furanones as potential anti-bacterial coatings on biomaterials

A major barrier to the long-term use of medical devices is development of infection. Staphylococcus epidermidis is one of the most common bacterial isolates from these infections with biofilm formation being their main virulence factor. Currently, antibiotics are used as the main form of therapy. However with the emergence of staphylococcal resistance, this form of therapy is fast becoming ineffective. In this study, the ability of a novel furanone antimicrobial compound to inhibit S. epidermidis adhesion and slime production on biomaterials was assessed. Furanones were physically adsorbed to various biomaterials and bacterial load determined using radioactivity. Slime production was assessed using a colorimetric method. Additionally, the effect of the furanone coating on material surface characteristics such as hydrophobicity and surface roughness was also investigated. The results of this study indicated that there was no significant change in the material characteristics after furanone coating. Bacterial load on all furanone-coated materials was significantly reduced (p<0.001) as was slime production (p<0.001). There is a potential for furanone-coated biomaterials to be used to reduce medical device-associated infections.

Adhesion of staphylococci to polymers with and without immobilized heparin in cerebrospinal fluid

Infections of cerebrospinal fluid (CSF) shunts constitute a serious clinical problem. The role of adhesion by coagulase negative staphylococci, the most common etiological agent, was examined in vitro to polyvinyl chloride (PVC), silicone, and to PVC and silicone with end-point attached (EPA) heparin. These are flexible materials commonly used in neurosurgical implants. Bacterial adhesion was quantitated by bioluminescence. The bacterial adhesion to biomaterial surfaces increased with increasing concentrations of bacterial cells. Scatchard plot analysis showed continuous negative (concave) slopes, indicating multiple interactions between biomaterial and bacteria. The thermodynamic studies showed a positive value of the standard entropy change at 37 degrees C, which indicates that hydrophobic interactions are important in bacterial adhesion to polymers. Incubation with CSF for 1 h decreased bacterial adhesion in 75% of the samples compared to incubation in buffer. Thus, the contribution of CSF proteins, like fibronectin, for the initial bacterial adhesion might be small. Heparinization of silicone and PVC decreased the numbers of adhered bacteria by 23 to 54% and 0 to 43% compared to unheparinized surfaces. Among putative inhibitors tested, suramin, chondroitin sulfate, and fucoidan inhibited adhesion to 81 +/- 19, 78 +/- 22, and 64 +/- 7%, respectively. These findings indicate that hydrophobic interactions play an important role, and heparinization rendering the biomaterial surface hydrophilic is therefore effective to reduce bacterial adhesion. Heparinized polymers incubated with putative inhibitors may be the optimal way to prevent shunt infections.

Bacterial surface properties of clinically isolated Staphylococcus epidermidis strains determine adhesion on polyethylene

The role of surface physiochemical properties of Staphylococcus epidermidis strains in adhesion to polyethylene (PE) was investigated under physiological flow conditions in phosphate buffered saline (PBS) and 1% platelet poor plasma (PPP). Four clinically isolated strains were divided into two groups: low and high relative hydrophobicity, and the F1198 and RP62A strains showing significantly greater hydrophobicity than the F21 and F1018 strains. In PBS, adhesion of all S. epidermidis strains was shear dependent from 0 to 15 dyn/cm2, after which adhesion becomes shear independent. Strains with higher surface hydrophobicity showed higher adhesion to PE, demonstrating the influence of bacterial surface hydrophobicity in nonspecific adhesion. Bacterial adhesion correlated well with bacterial surface hydrophobicity at low shear stresses (0-8 dyn/cm2). In 1% PPP, adhesion of all strains dramatically decreased and we found no correlation between bacterial surface hydrophobicity and adhesion. The presence of plasma proteins reduced nonspecific adhesion. S. epidermidis surface charge did not correlate with bacterial adhesion in either test media. The results suggested that S. epidermidis surface hydrophobicity may mediate nonspecific adhesion to PE at low shear stresses in protein-free media.

Slime production, adherence and hydrophobicity in coagulase-negative staphylococci causing peritonitis in peritoneal dialysis

Attachment of coagulase-negative staphylococci to plastic surfaces by means of hydrophobic interaction and slime production may be important in producing catheter associated infections. In continuous ambulatory peritoneal dialysis (CAPD), the relationship between these properties and disease is unclear and the effect of dialysate fluid is not considered. For a collection of coagulase-negative staphylococci from CAPD patients, slime production and adherence were measured by colorimetric methods and hydrophobicity was determined by autoaggregation in ammonium sulphate solution. Comparison of 73 nasal isolates with 69 isolates from peritonitis showed no significant differences with respect to three properties, with the exception of a greater adherence of peritoneal isolates in dialysate because of a greater proportion of staphylococcal species other than Staphylococcus epidermidis. Fewer strains showed adherence in dialysate (12/142 8.5%) than in broth (94/142 66%) but the proportion of strains producing slime was similar. The milieu of the bacteria rather than the organisms themselves may be of greater importance in the establishment of infection.

The role of Serratia marcescens in soft contact lens associated ocular infections. A review

Serratia marcescens is a Gram negative rod which for a century and a half was considered a harmless saphrophyte. However, medical technology and the use of antibacterial agents have created ecological niches for this bacterium, which is now a medical problem. The bacterium is encountered in connection with contact lens keratitis, often associated with contaminated contact lens solutions. The concentrations of chlorhexidin and thiomersal required in contact lens solution to suppress the bacterium have been proved toxic to the eye. Modern contact lens solutions with biguanids have rapid killing kinetics, while in solutions with polyquaternium S. marcescens can survive in reduced numbers for up to 72 hours. The adherence of a specific isolate of Serratia to hydrogel lenses increased with decreased water content of the lenses. However, there has been no correlation between hydrophobicity markers or hemagglutinins and adherence to contact lenses or urinary tract epithelium. When handling medical plastic devices, such as contact lenses, strictly enforced hygiene remains the most important method to combat environmental bacteria such as Serratia marcescens.