Henny C. van der Mei

In vitro and in vivo antimicrobial activity of covalently coupled quaternary ammonium silane coatings on silicone rubber

Biomaterial-centered infection is a dreaded complication associated with the use of biomedical implants. In this paper, the antimicrobial activity of silicone rubber with a covalently coupled 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride (QAS) coating was studied in vitro and in vivo. Gram-positive Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH, 102, and Gram-negative Esherichia coli O2K2 and Pseudomonas aeruginos AK1 were seeded on silicone rubber with and without QAS-coating, in the absence or presence of adsorbed human plasma proteins. The viability of the adherent bacteria was determined using a live/dead fluorescent stain and a confocal laser scanning microscope. The coating reduced the viability of adherent staphylococci from 90% to 0%), and of Gram-negative bacteria from 90% to 25% while the presencc of adsorbed plasma proteins had little influence. The biomaterials were also subcutaneously implanted in rats for 3 or 7 days, while pre- or postoperatively seeded with S. aureus ATCC 12600. Preoperative seeding resulted in infection of 7 out of 8 silicone rubber implants against 1 out of 8 QAS-coated silicone rubber implants. Postoperative seeding resulted in similar infection incidences on both implant types, but the numbers of adhering bacteria were 70% lower on QAS-coated silicone rubber. In conclusion, QAS-coated silicone rubber shows antimicrobial properties against adhering bacteria, both in vitro and in vivo.

Microbiota restoration: natural and supplemented recovery of human microbial communities

In a healthy host, a balance exists between members of the microbiota, such that potential pathogenic and non-pathogenic organisms can be found in apparent harmony. During infection, this balance can become disturbed, leading to often dramatic changes in the composition of the microbiota. For most bacterial infections, nonspecific antibiotics are used, killing the non-pathogenic members of the microbiota as well as the pathogens and leading to a substantial delay in the restoration of a healthy microbiota. However, in some cases, infections can self-resolve without the intervention of antibiotics. In this Review, we explore the mechanisms underlying microbiota restoration following insult (antibiotic or otherwise) to the skin, oral cavity, and gastrointestinal and urogenital tracts, highlighting recovery by natural processes and after probiotic administration.

Biomaterial-Associated Infection: Locating the Finish Line in the Race for the Surface

This Review discusses approaches to developing infection-reducing biomaterials that strike a balance between host tissue integration and prevention of microbial attachment. NONE Biomaterial-associated infections occur on both permanent implants and temporary devices for restoration or support of human functions. Despite increasing use of biomaterials in an aging society, comparatively few biomaterials have been designed that effectively reduce the incidence of biomaterial-associated infections. This review provides design guidelines for infection-reducing strategies based on the concept that the fate of biomaterial implants or devices is a competition between host tissue cell integration and bacterial colonization at their surfaces.

How a fungus escapes the water to grow into the air

Fungi are well known to the casual observer for producing water-repelling aerial moulds and elaborate fruiting bodies such as mushrooms and polypores. Filamentous fungi colonize moist substrates (such as wood) and have to breach the water-air interface to grow into the air. Animals and plants breach this interface by mechanical force. Here, we show that a filamentous fungus such as Schizophyllum commune first has to reduce the water surface tension before its hyphae can escape the aqueous phase to form aerial structures such as aerial hyphae or fruiting bodies. The large drop in surface tension (from 72 to 24 mJ m-2) results from self-assembly of a secreted hydrophobin (SC3) into a stable amphipathic protein film at the water-air interface. Other, but not all, surface-active molecules (that is, other class I hydrophobins and streptofactin from Streptomyces tendae) can substitute for SC3 in the medium. This demonstrates that hydrophobins not only have a function at the hyphal surface but also at the medium-air interface, which explains why fungi secrete large amounts of hydrophobin into their aqueous surroundings.

Infection of orthopedic implants and the use of antibiotic-loaded bone cements - A review

Infections by bacteria are a serious complication following orthopedic implant surgery, that can usually only be cured by removing the implant, since the biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. Over the past few decades, attempts have been made to prevent and cure orthopedic implant infections by incorporating antibiotics in polymethylmethacrylate bone cements, in primary and revision surgery. However, the clinical efficacy of antibiotic-releasing bone cements is not accepted by all and the long-term exposure to low doses from antibiotic-releasing bone cements in patients is strongly related to the emerging threat of antibiotic resistance in medicine today. In this article, we start by reviewing the mechanisms governing the formation of an infectious biofilm on orthopedic implant materials, the release mechanisms and properties of clinically-used, antibiotic-loaded bone cements. The clinical efficacy of antibiotic-loaded bone cements is evaluated analyzing separatedly the prophylactic and therapeutic uses of these products.

Microbial Adhesion in Flow Displacement Systems

SUMMARY Flow displacement systems are superior to many other (static) systems for studying microbial adhesion to surfaces because mass transport and prevailing shear conditions can be adequately controlled and notoriously ill-defined slight rinsing steps to remove so-called “loosely adhering organisms” can be avoided. In this review, we present the basic background required to calculate mass transport and shear rates in flow displacement systems, focusing on the parallel plate flow chamber as an example. Critical features in the design of flow displacement systems are discussed, as well as different strategies for data analysis. Finally, selected examples of working with flow displacement systems are given for diverse biomedical applications.

Analysis of Bacterial Detachment from Substratum Surfaces by the Passage of Air-Liquid Interfaces

ABSTRACT A theoretical analysis of the detachment of bacteria adhering to substratum surfaces upon the passage of an air-liquid interface is given, together with experimental results for bacterial detachment in the absence and presence of a conditioning film on different substratum surfaces. Bacteria (Streptococcus sobrinus HG1025,Streptococcus oralis J22, Actinomyces naeslundii T14V-J1, Bacteroides fragilis 793E, andPseudomonas aeruginosa 974K) were first allowed to adhere to hydrophilic glass and hydrophobic dimethyldichlorosilane (DDS)-coated glass in a parallel-plate flow chamber until a density of 4 × 106 cells cm−2 was reached. ForS. sobrinus HG1025, S. oralis J22, and A. naeslundii T14V-J1, the conditioning film consisted of adsorbed salivary components, while for B. fragilis 793E andP. aeruginosa 974K, the film consisted of adsorbed human plasma components. Subsequently, air bubbles were passed through the flow chamber and the bacterial detachment percentages were measured. For some experimental conditions, like with P. aeruginosa974K adhering to DDS-coated glass and an air bubble moving at high velocity (i.e., 13.6 mm s−1), no bacteria detached upon passage of an air-liquid interface, while for others, detachment percentages between 80 and 90% were observed. The detachment percentage increased when the velocity of the passing air bubble decreased, regardless of the bacterial strain and substratum surface hydrophobicity involved. However, the variation in percentages of detachment by a passing air bubble depended greatly upon the strain and substratum surface involved. At low air bubble velocities the hydrophobicity of the substratum had no influence on the detachment, but at high air bubble velocities all bacterial strains were more efficiently detached from hydrophilic glass substrata. Furthermore, the presence of a conditioning film could either inhibit or stimulate detachment. The shape of the bacterial cell played a major role in detachment at high air bubble velocities, and spherical strains (i.e., streptococci) detached more efficiently than rod-shaped organisms. The present results demonstrate that methodologies to study bacterial adhesion which include contact with a moving air-liquid interface (i.e., rinsing and dipping) yield detachment of an unpredictable number of adhering microorganisms. Hence, results of studies based on such methodologies should be referred as “bacterial retention” rather than “bacterial adhesion”.

Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces.

Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the following three hypotheses. 1. A strong hydrodynamic shear force to prevent adhesion relates to a strong hydrodynamic shear force to detach an adhering organism. 2. A weak hydrodynamic shear force to detach adhering bacteria implies that more bacteria will be stimulated to detach by passing an air-liquid interface (an air bubble) through the flow chamber. 3. DLVO (Derjaguin, Landau, Verwey, Overbeek) interactions determine the characteristic hydrodynamic shear forces to prevent adhesion and to detach adhering micro-organisms as well as the detachment induced by a passing air-liquid interface. F(prev) varied from 0.03 to 0.70 pN, while F(det) varied from 0.31 to over 19.64 pN, suggesting that after initial contact, strengthening of the bond occurs. Generally, it was more difficult to detach bacteria from DDS-coated glass than from hydrophilic glass, which was confirmed by air bubble detachment studies. Calculated attractive forces based on the DLVO theory (F(DLVO)) towards the secondary interaction minimum were higher on glass than on DDS-coated glass. In general, all three hypotheses had to be rejected, showing that it is important to distinguish between forces acting parallel (hydrodynamic shear) and perpendicular (DLVO, air-liquid interface passages) to the substratum surface.

Bacterial adhesion and growth on a polymer brush-coating

Biomaterials-related infections pose serious problems in implant surgery, despite the development of non-adhesive coatings. Non-adhesive coatings, like polymer brush-coatings, have so far only been investigated with respect to preventing initial bacterial adhesion, but never with respect to effects on kinetics of bacterial growth. Here, we compare adhesion and 20 h growth of three bacterial strains (Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa) on pristine and brush-coated silicone rubber in a parallel plate flow chamber. Brush-coatings were made using a tri-block copolymer of polyethylene oxide (PEO) and polypropylene oxide (PPO). Brush-coatings prevented adhesion of staphylococci to below 5 x 10(5)cm(-2) after 30 min, which is a 10-fold reduction compared to pristine silicone rubber. Biofilms grew on both brush-coated and pristine silicone rubber, while the viability of biofilms on brush-coatings was higher than on pristine silicone rubber. However, biofilms on brush-coatings developed more slowly and detached almost fully by high fluid shear. Brush-coating remained non-adhesive after S. epidermidis biofilm formation and subsequent removal whereas a part of its functionality was lost after removal of S. aureus biofilms. Adhesion, growth and detachment of P. aeruginosa were not significantly different on brush-coatings as compared with pristine silicone rubber, although here too the viability of biofilms on brush-coatings was higher. We conclude that polymer brush-coatings strongly reduce initial adhesion of staphylococci and delay their biofilm growth. In addition, biofilms on brush-coatings are more viable and easily removed by the application of fluid shear.

Residual gentamicin-release from antibiotic-loaded polymethylmethacrylate beads after 5 years of implantation

In infected joint arthroplasty, high local levels of antibiotics are achieved through temporary implantation of non-biodegradable gentamicin-loaded polymethylmethacrylate beads. Despite their antibiotic release, these beads act as a biomaterial surface to which bacteria preferentially adhere, grow and potentially develop antibiotic resistance. In routine clinical practice, these beads are removed after 14 days, but for a variety of reasons, we were confronted with a patient in which these beads were left in situ for 5 years. Retrieval of gentamicin-loaded beads from this patient constituted an exceptional case to study the effects of long-term implantation on potentially colonizing microflora and gentamicin release. Gentamicin-release test revealed residual antibiotic release after being 5 years in situ and extensive microbiological sampling resulted in recovery of a gentamicin-resistant staphylococcal strain from the bead surface. This case emphasizes the importance of developing biodegradable antibiotic-loaded beads as an antibiotic delivery system.