Long-term Antimicrobial Effect Research Articles

Self-triggered carboxymethyl chitosan hydrogel for the convenient sustained release of ClO2 gas with environmental stability and long-term antimicrobial effect.

Challenges associated with the storage and uncontrolled release of ClO2 gas present significant hurdles to its practical application. Herein, a clever strategy for self-triggering the sustained release of chlorine dioxide (ClO2) gas is proposed by crosslinking carboxymethyl chitosan (CMCS) with Zn2+ to construct a novel CMCS-Zn@NaClO2 gel with eco-friendly, environmental stability, and convenient, long term, and efficient antibacterial activity. The precursor (NaClO2) in the CMCS solution was alkaline and triggered by the acidic Zn(NO3)2·6H2O solution to achieve sustained self-triggering ClO2 release. The ClO2 gas self-release could be sustained on demand at different temperatures for at least 20 days due to the environmental structure stability of the gel. The hydrogels showed an increase in pore size after sustained release. Molecular dynamics simulations showed the spontaneous release of ClO2 gas at room temperature and the contraction of the CMCS agglomeration, which were consistent with the macroscopic behaviour. The gel displayed a long-acting and high antibacterial efficacy, resulting in a bacteria-killing rate of over 99.9% (inhibitory concentrations of 2.5 mg mL-1 against E. coli and 0.16 mg mL-1 against S. aureus). The hydrogels could effectively extend the shelf life of fruits and demonstrated an excellent wide range of antibacterial properties. This work provides a new approach to solving the storage difficulty of ClO2 gas and offers a fresh perspective on the design of materials with convenient self-triggering release by a precursor, as well as the relationship between the material microstructure and sustained-release behaviour.

Antimicrobial geopolymer paints based on modified natural zeolite

Many antimicrobial coatings deliver a peak release of antimicrobial agent at an early age, after which they lost antimicrobial activity over time. In the present study a novel geopolymer paints with long term antimicrobial activity were developed based on natural zeolite modified with silver and copper ions. The obtained geopolymer paints were applied by brushing on concrete, ceramic, gypsum paperboard and steel. The coating was characterized by excellent adhesive strength and hiding properties. The long-term antimicrobial effect was evaluated by accelerated aging in carbonation chamber. Microstructural changes were analyzed by powder X-ray diffraction and Fourier transformed infrared spectroscopy. Cytotoxicity, antibacterial, antifungal and virucidal properties were investigated on raw and carbonated geopolymer paints. Geopolymer paints based on modified natural zeolite seems promising antimicrobial coating material that can be implemented in the global fight against the spread of diseases and pathogens.

Injectable sodium alginate hydrogel loaded with plant polyphenol-functionalized silver nanoparticles for bacteria-infected wound healing

A novel injectable hydrogel dressing (GA@AgNPs-SA) with long-term antimicrobial effect is developed that can accelerate the closure of bacteria-infected wounds. The hydrogel dressing was prepared by cross-linking sodium alginate molecular chains and gallic acid functionalized silver nanoparticles (GA@AgNPs) via calcium ions to form a three-dimensional network. The hydrogel dressing demonstrates excellent biocompatibility and can achieve a sustainable release of silver ions, ensuring a long-term antibacterial activity and inhibiting biofilm formation. Moreover, an in vivo study demonstrates that the GA@AgNPs-SA hydrogel can effectively decrease the expression of IL-6 and TNF-α to alleviate the inflammatory response, and promote angiogenesis by upregulating CD31, α-SMA and VEGF expression, thus significantly accelerating the repair of infected wounds. Given these interesting properties, this antibacterial hydrogel has great potential for application in the clinical care of bacteria-infected wounds.

Long-term antimicrobial effect of polylactide-based composites suitable for biomedical use

This work deals with the preparation and characterization of antimicrobial polymeric composite materials based on polylactide, which is currently widely investigated to produce temporary implants. Polylactide was blended with antimicrobial fillers: silver, hexadecylpyridinium or hexadecyltrimethylammonium bromides anchored on vermiculite or graphene oxide matrices in an amount of 1% wt. The prepared samples were characterized by conventional methods, further they were exposed to degradation tests in physiological saline conditions and characterized for their antimicrobial properties using common pathogen microorganisms. It has been proven that the prepared polylactide composites change their antimicrobial effects after being in physiological saline of pH 7 and 9 for 0–6 months. The weight of the composites changed by about 10%, and antimicrobial properties were growing over time. The effectiveness of the composites was confirmed for 6 months at minimum. Therefore, they are suitable for the preparation of temporary stents, catheters or implants suitable for fracture fixation.

Green Synthesis and Characterization of Antimicrobial Synergistic AgCl/BAC Nanocolloids.

All over the world, one of the major challenges is the green synthesis of potential materials against antimicrobial resistance and viruses. This study demonstrates a simple method like chemistry lab titration to synthesize green, facile, scalable, reproducible, and stable synergistic silver chloride/benzyldimethylhexadecyl-ammonium chloride (AgCl/BAC) colloidal Nanoantimicrobials (NAMs). Nanocolloidal dispersions of AgCl in an aqueous medium are prepared by using silver nitrate (AgNO3) as precursor and BAC as both sources of chloride and stabilizer, holding an asymmetric molecular structure. The synthetic approach is scalable and green. Both the morphology and stability of AgCl/BAC nanocolloids (NCs) were investigated as a function of different molar fractions of the reagents. AgCl/BAC NCs were characterized by transmission electron microscopy (TEM) and X-ray photoelectron and UV–vis spectroscopies. Zeta potential measurements revealed increasing positive potential values at every stage of the synthesis. Size distribution and hydrodynamic diameter of the particles were measured by dynamic light scattering (DLS), which predicted the formation of BAC layered structures associated with the AgCl nanoparticles (NPs). Small-angle X-ray scattering (SAXS) experiments verify the thickness of the BAC bilayer around AgCl. The produced AgCl/BAC NCs probably have synergistic antimicrobial properties from the AgCl core and the biocide BAC shell. AgCl/BAC NCs stability over months was investigated. The experimental evidence supports the morphological stability of the AgCl/BAC NCs, while higher positive zeta potential values anticipate a long-term antimicrobial effect: a higher surface charge causes NPs to be potentially more lethal to bacteria. AgCl/BAC antimicrobial aqueous colloidal suspensions will be used as additives for the industrial production of antimicrobial coatings.

Release characterization and biological effect of Glass Ionomer Functionalized with two different chlorohexidine derivatives: an in vitro study

Objective: To evaluate the effect of adding two different chlorohexidine derivatives; chlorhexidine hexametaphosphate and chlorhexidine digluconate to glass ionomer at three different concentrations (0.25%, 0.75%and 1.5%) regarding the antibacterial effect, chlorhexidine release and fluoride release. Methods: A total of 405 specimens were prepared and tested after 7 days, 3 months and 6 months of storage in distilled water (n=5).For testing antibacterial effect, chlorhexidine release and fluoride release, the mix was packed in a ready-made Split Teflon molds to obtain disc-shaped specimen with dimensions 10 mm in diameter and 2 mm thickness according to ISO standardizations. One-way ANOVA and One-way repeated measure ANOVA test were used for statistical analysis of data. Results: The incorporation of chlorhexidine into ChemFil Superior glass ionomer cement in both derivatives has high significance ability to provide a long-term antimicrobial effect on Streptococcus mutans and Lactobacillius acidophilus. The chlorhexidine release was increased by adding chlorhexidine in both derivatives to GIC than the unmodified Glass-ionomer cement for study duration. However, the fluoride release was decreased in the modified specimens than the original one. Conclusion: Addition of chlorhexidine enhanced the antibacterial effect of the glass ionomer and chlorhexidine release. However, fluoride release was reduced than original

Effect of Cavity Cleanser With Long-Term Antibacterial and Anti-Proteolytic Activities on Resin-Dentin Bond Stability.

ObjectiveSecondary caries caused by oral microbiome dysbiosis and hybrid layer degradation are two important contributors to the poor resin–dentin bond durability. Cavity cleansers with long-term antimicrobial and anti-proteolytic activities are in demand for eliminating bacteria-induced secondary caries and preventing hybrid layers from degradation. The objectives of the present study were to examine the long-term antimicrobial effect and anti-proteolytic potential of poly(amidoamine) dendrimers with amino terminal groups (PAMAM-NH2) cavity cleanser.MethodsAdsorption tests by attenuated total reflectance–infrared (ATR-IR) spectroscopy and confocal laser scanning microscopy (CLSM) were first performed to evaluate whether the PAMAM-NH2 cavity cleanser had binding capacity to dentin surface to fulfill its relatively long-term antimicrobial and anti-proteolytic effects. For antibacterial testing, Streptococcus mutans, Actinomyces naeslundii, and Enterococcus faecalis were grown on dentin surfaces, prior to the application of cavity cleanser. Colony-forming unit (CFU) counts and live/dead bacterial staining were performed to assess antibacterial effects. Gelatinolytic activity within the hybrid layers was directly detected by in situ zymography. Adhesive permeability of bonded interface and microtensile bond strength were employed to assess whether the PAMAM-NH2 cavity cleanser adversely affected resin–dentin bonding. Finally, the cytotoxicity of PAMAM-NH2 was evaluated by the Cell Counting Kit-8 (CCK-8) assay.ResultsAdsorption tests demonstrated that the binding capacity of PAMAM-NH2 on dentin surface was much stronger than that of 2% chlorhexidine (CHX) because its binding was strong enough to resist phosphate-buffered saline (PBS) washing. Antibacterial testing indicated that PAMAM-NH2 significantly inhibited bacteria grown on the dentin discs as compared with the control group (p < 0.05), which was comparable with the antibacterial activity of 2% CHX (p > 0.05). Hybrid layers conditioned with PAMAM-NH2 showed significant decrease in gelatin activity as compared with the control group. Furthermore, PAMAM-NH2 pretreatment did not adversely affect resin–dentin bonding because it did not decrease adhesive permeability and microtensile strength. CCK-8 assay showed that PAMAM-NH2 had low cytotoxicity on human dental pulp cells (HDPCs) and L929.ConclusionsPAMAM-NH2 cavity cleanser developed in this study could provide simultaneous long-term antimicrobial and anti-proteolytic activities for eliminating secondary caries that result from a dysbiosis in the oral microbiome and for preventing hybrid layers from degradation due to its good binding capacity to dentin collagen matrix, which are crucial for the maintenance of resin–dentin bond durability.

Аntibacterial inorganic agents: efficiency of using multicomponent systems

Metal and metal oxide nanoparticles (NPs) are promising antibacterial agents. They have a broad antimicrobial activity against both Gram-positive and Gram-negative bacteria, viruses, and protozoans. The use of NPs reduces the possibility of the microbial resistance development. This review briefly shows the general mechanisms and the main factors of antibacterial activity of NPs. In this article, a comprehensive review of the recent researches in the field of new antimicrobial agents with superior long-term bactericidal activity and low toxicity is provided. The review gives the examples of synthesis of double and triple nanocomposites based on following oxides: CuO, ZnO, Fe3O4, Ag2O, MnO2, etc. including metal and nonmetal doped nanocomposites (for example with Ag, Ce, Cr, Mn, Nd, Co, Sn, Fe, N, F, etc.). Compared with bactericidal action of individual oxides, the nanocomposites demonstrate superior antibacterial activity and have synergistic effects. For example, the antimicrobial activity of ZnO against both Gram-positive and Gram-negative bacteria was increased by -100% by formation of triple nanocomposites ZnO—MnO2—Cu2O or ZnO—Ag2O—Ag2S. Similar effect was showed for Ce-doped ZnO and Zn-doped CuO. The present article also provides the examples of nanocomposites containing NPs and organic (chitosan, cellulose, polyvinylpyrrolidone, biopolymers, etc.) or inorganic materials with special structure (graphene oxide, TiO2 nanotubes, silica) which demonstrate controlled release and longterm antibacterial activity. All of the considered nanocomposites and their combinations have a pronounced long-term antimicrobial effect including against antibiotic-resistant strains. They are able to prevent the formation of microbial biofilms on biotic and abiotic surfaces, have low toxicity to eukaryotic cells, demonstrate anti-inflammatory and woundhealing properties in compositions with polymers (sodium alginate, collagen, polyvinylpyrrolidone, etc.). The use of nanoscale systems can solve several important practical problems at the same time: saving of long-term antimicrobial activities while reducing the number of compounds, creation of new antimicrobial agents with low toxicity and reduced environmental impact, development of new biocidal materials, including new coatings for effective antimicrobial protection of medical devices.

Development of AgCl-TiO2 xerogels entrapped antibacterial polyacrylonitrile membranes: The effect of high salinity water on silver release, antibiofouling and antibacterial efficacies

Silver-containing antibacterial membranes are commonly used to control biofouling during bacteria filtration. Unfortunately, fast and uncontrolled release of silver to water is a challenge since this causes mass accumulation of silver in water resources and insufficient long-term antimicrobial effect. To overcome these disadvantages, we propose to add AgCl-TiO2 xerogels (0–0.8 wt%) in the polyacrylonitrile membranes. The long-term silver retaining of the membranes was evaluated by measuring the silver release under filtration of deionized water in the absence and the presence of 1 M NaCl up to 5 days. The antibiofouling and the antibacterial efficacies were determined by measuring the changes in antibacterial activity and DI water flux of the membranes at the end of 5 days of E. coli filtration. The 0.2 wt% AgCl-TiO2 xerogel incorporated polyacrylonitrile membrane demonstrated a constant ~1 μg of silver release/cm2 per filtration cycle after a total filtration of 0.05 L/cm2 with 1 M NaCl solution. Additionally, it showed antibacterial efficacy and ~100% recovery of deionized water flux by simple backwashing with water after having been used in many E. coli filtration cycles. Thus, this membrane could potentially be used up to ~5.8 years for 8000 h a year for the filtration of high salinity water. Statement of noveltySilver-containing antibacterial membranes are commonly used to control biofouling during bacteria filtration. Uncontrolled release of silver from the membrane causes massive silver accumulation in water which in turn leads to contamination of water resources and threat to aquatic organisms. Although silver release is strongly influenced by the salinity of water, the release data was collected through filtration of pure DI water or tap water in literature. To overcome the shortcomings of the published studies, we propose to use AgCl-TiO2 xerogels in membranes due to low solubility of AgCl in water and measure the release by filtering high-salinity water.

Phage-delivered sensitisation with subsequent antibiotic treatment reveals sustained effect against antimicrobial resistant bacteria

Temperate phages integrated with clustered regularly interspaced short palindromic repeat (CRISPR)/Cas systems have been gaining attention as potential strategies for combating bacteria resistant to antimicrobials. To further advance this technology, phage recombination procedure should be improved, and the bactericidal effect should be examined in detail and compared with conventional lytic phage strategy. The possibility of the emergence of mutational resistance, a phenomenon commonly observed with lytic phage therapy, should be illustrated.Methods: Here, we developed a novel one-step cloning method to fulfil the recombination of CRISPR/Cas9 system within the genome of a new isolated lysogenic Escherichia coli phage. Then, we proposed and developed a phage-delivered resistance eradication with subsequent antibiotic treatment (PRESA) strategy. The removal efficiency and antimicrobial effect of the plasmids were analysed. Long-term antimicrobial effect was evaluated by continued OD600 monitoring for 240 hours to illustrate the potential mutational resistance, compared with the lytic phage strategy. The treatment effect of PRESA was evaluated in vivo by determining bacterial loads in the skin and intestine of infected mice, in contrast with lytic phage therapy. Genome sequencing was performed to identify mutations in bacterial cells treated with phage strategies.Results: Phage-delivered CRISPR targeting efficiently eradicated and blocked the transfer of the antibiotic resistance plasmid. PRESA decreased the bacterial load by over 6- and 5-logs in vitro and in vivo, respectively. Importantly, while lytic phages induced mutational phage resistance at 24 h in vitro and 48 hours in vivo, PRESA demonstrated a constant effect and revealed no resistant mutants. Genes involved in DNA mismatch repair were upregulated in cells undergoing Cas9-based plasmid cleavage, which may reduce the development of mutations.Conclusion: The PRESA strategy for eradicating resistant bacteria showed high bactericidal efficacy and a sustained inhibition effect against resistant bacteria. By restoring the efficacy of low-cost antibiotics, PRESA could be developed as an efficient and economical therapy for infections of antibiotic resistant bacteria.

Responsive antimicrobial dental adhesive based on drug-silica co-assembled particles

Most dental resin composite restorations are replacements for failing restorations. Degradation of the restoration-tooth margins by cariogenic bacteria results in recurrent caries, a leading cause for restoration failure. Incorporating antimicrobial agents in dental adhesives could reduce interfacial bacterial count and reduce recurrent caries rates, inhibit interfacial degradation, and prolong restoration service life, while minimizing systemic exposure. Direct addition of antimicrobial compounds into restorative materials have limited release periods and could affect the integrity of the material. Attempts to incorporate antimicrobial within mesoporous silica nanoparticles showed theoretical promise due to their physical robustness and large available internal volume, yet yielded short-term burst release and limited therapeutic payload.We have developed novel broad-spectrum antimicrobial drug-silica particles co-assembled for long-term release and high payload incorporated into dental adhesives. The release of the drug, octenidine dihydrochloride, is modulated by the oral degradative environment and mathematically modeled to predict effective service life. Steady-state release kills cariogenic bacteria, preventing biofilm formation over the adhesive surface, with no toxicity. This novel material could extend dental restoration service life and may be applied to other long-term medical device-tissue interfaces for responsive drug release upon bacterial infection. Statement of SignificanceThis study describes a novel dental adhesive that includes a broad-spectrum antimicrobial drug-silica co-assembled particles for long-term antimicrobial effect. The release of the drug, octenidine dihydrochloride, is modulated by the oral degradative environment and mathematically modeled to predict effective release throughout the service life of the restoration. Steady-state drug-release kills caries-forming bacteria, preventing biofilm formation over the adhesive surface, without toxicity. This novel material could extend dental restoration service life and may be applied to other long-term medical device-tissue interfaces for responsive drug release upon bacterial infection. Since recurrent cavities (caries) caused by bacteria are the major reason for dental filling failure, this development represents a significant contribution to the biomaterials field in methodology and material performance.

Core-Shell Silver Nanoparticles in Endodontic Disinfection Solutions Enable Long-Term Antimicrobial Effect on Oral Biofilms.

To achieve effective long-term disinfection of the root canals, we synthesized core-shell silver nanoparticles (AgNPs@SiO2) and used them to develop two irrigation solutions containing sodium phytate (SP) and ethylene glycol-bis(β-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA), respectively. Ex vivo studies with instrumented root canals revealed that the developed irrigation solutions can effectively remove the smear layer from the dentinal surfaces. Further in vitro experiments with single- and multispecies biofilms demonstrated for the first time that AgNPs@SiO2-based irrigation solutions possess excellent antimicrobial activities for at least 7 days, whereas the bare AgNPs lose the activity almost immediately and do not show any antibacterial activity after 2 days. The long-term antimicrobial activity exhibited by AgNPs@SiO2 solutions can be attributed to the sustainable availability of soluble silver, even after 7 days. Both solutions showed lower cytotoxicity toward human gingival fibroblasts compared to the conventionally used solution (3% NaOCl and 17% EDTA). Irrigation solutions containing AgNP@SiO2 may therefore be highly promising for applications needing a long-term antimicrobial effect.

Long-term antimicrobial effect of nisin released from electrospun triaxial fiber membranes.

The increase in drug resistant pathogens has driven the need for alternative treatments that are effective against resistant bacteria and do not contribute to drug resistance. Nisin is an excellent model bacteriocin for antimicrobials because of its size and mode of action, and has been extensively used as FDA-approved food preservatives without any problematic resistance growth in bacteria during past decades. Nisin-containing fibers have been previously reported using conventional electrospinning but sustained antimicrobial effect has not been obtained. Here, we report the encapsulation of nisin into a multi-layered nanofiber construct using triaxial electrospinning in order to obtain a long-term antimicrobial activity. This will be highly beneficial in many applications, such as protective textiles, food packaging and cancer therapy.

Development of long-term antimicrobial poly(methyl methacrylate) by incorporating mesoporous silica nanocarriers

ObjectivePoly(methyl methacrylate) (PMMA) used as removable denture bases or orthodontic appliances has relatively poor antimicrobial properties, which accelerate oral infection and induce unfavorable odors. Mesoporous silica nanoparticles (MSNs) have been highlighted as a potential additive to overcome this issue because of their drug-loading capacity. Here, we present the long-term antimicrobial effect of MSN-incorporated PMMA with drug-loading capacity. MethodsAfter the MSNs were characterized, MSN incorporation into chemically activated PMMA (0.5, 1, 2.5 or 5wt%) relative to the methyl methacrylate powder by mass was fabricated into a rectangular specimen (1.4×3.0×19.0mm) for a 3-point flexural test at a speed of 1mm/min or a disk (∅=11.5mm and d=1.5mm) for investigation of its antimicrobial effects. ResultsA typical spherical morphology with a well-ordered mesoporous structure of the MSNs was visualized and is beneficial for loading drugs and combining in matrixes. Among the tested levels of MSN incorporation in PMMA (0.5, 1, 2.5 or 5wt%), only 5wt% decreased the flexural strength (p<0.05), whereas the flexural modulus was not significantly decreased (p>0.05). The surface roughness and surface energy were increased with 2.5wt% or 5wt% incorporation. An anti-adherent effect against Candida albicans and Streptococcus oralis after 1h of attachment was only observed with 2.5 and 5wt% incorporation compared to a lack of MSNs (p<0.05). A long-term antimicrobial effect was observed for 2 weeks with 2.5wt% MSN-incorporated PMMA when amphotericin B was loaded into the MSNs on the PMMA surface. SignificanceThe long-term antimicrobial performance after loading amphotericin B into the MSN-incorporated PMMA suggests the potential clinical usefulness of MSN-incorporated PMMA resin.

Antimicrobial properties of Zr–Cu–Al–Ag thin film metallic glass

Metallic glass as a prominent class of structure and multifunctional materials exhibits several unique properties in mechanical, electrochemical, and thermal properties. This study aimed to realize the advantage of biomedical application and to promote the attainable size of metallic glasses by the physical vapor deposition. The Zr–Cu–Al–Ag thin film metallic glass (TFMG) was deposited on silicon wafer and SUS304 stainless steel substrates by magnetron sputtering with single target. For X-ray diffraction analysis, all TFMGs revealed typical broad peaks around the incident angle of 30 to 50°, suggesting that coatings possess amorphous structure. In addition, diffuse halo ring patterns of transmission electron microscopy indicated a fine amorphorization for TFMG via sputtering process. The variation of surface roughness showed that TFMG derived from higher power of metallic targets revealed rougher morphology. Besides, the roughness of SUS304 stainless steel substrate significantly reduced from 7nm to about 1nm after TFMGs were deposited.The microbes of Candida albicans, Escherichia coli, and Pseudomonas aeruginosa were used and cultivated on the TFMG coatings with medium to investigate the antimicrobial properties. In the incubation experiment, the growth of each microbe was recorded by a digital photography system and the growth area was calculated by image processing software. The growth area of the microbes on the TFMG was mostly smaller than that on SUS304 stainless steel ones within incubation time of 72h, indicating that the TFMGs reveal better antimicrobial capability. Moreover, the coatings exhibit a particularly long-term antimicrobial effect for P. aeruginosa. In summary, the Zr–Cu–Al–Ag prepared by sputtering with a single target device presented superior glass forming ability, and coatings with copper and silver constituents revealed significantly antimicrobial properties. Besides, the surface roughness is another factor to affect the biological activities, suggesting that microbes are difficult to attach and move on an ultra-smooth surface. It is demonstrated in this study that the TFMGs extend attainable size of the metallic glass and show a potential application in medical related field.

Antimicrobial electrospun nanofibers of cellulose acetate and polyester urethane composite for wound dressing

In this study, a series of nanofibrous membranes were prepared from cellulose acetate (CA) and polyester urethane (PEU) using coelectrospinning or blend-electrospinning. The drug release, in vitro antimicrobial activity and in vivo wound healing performance of the nanofiber membranes were evaluated for use as wound dressings. To prevent common clinical infections, an antimicrobial agent, polyhexamethylene biguanide (PHMB) was incorporated into the electrospun fibers. The presence of CA in the nanofiber membrane improved its hydrophilicity and permeability to air and moisture. CA fibers became slightly swollen upon contacting with liquid phase. CA not only increased the liquid uptake but also created a moist environment for the wound, which accelerated wound recovery. PHMB release dynamics of the membranes was controlled by the structure and component ratios of the membranes. The lower ratio of CA: PEU helped to preserve the physical and thermal properties of the membranes, and also reduced the burst release effectively and slowed down diffusion of PHMB during in vitro tests. The controlled-diffusion membranes exerted long-term antimicrobial effect for wound healing.

Short- and long-term bacterial inhibiting effect of high concentrations of glycerol used in the preservation of skin allografts

Human skin allografts are important in the treatment of severe burns. Transplantation of skin allografts can cause bacterial transmission. Glycerol in higher concentrations is an appropriate storage medium for allograft cadaver skin and has been attributed an antimicrobial effect. We investigated this effect in more detail. First, the minimal inhibitory concentration of glycerol was determined for 13 bacteria and 1 yeast. This gives an indication about an immediate (20 h of incubation) antibacterial effect of glycerol. Second, effect of glycerol in the long-term was studied. Therefore, the survival time was determined for 11 different bacteria suspended in different concentrations of glycerol (50% and 85%) and incubated at three temperatures (4, 24, and 36 °C). The minimal inhibitory concentration exceeded 256 μg/mL, thus glycerol had no direct inhibitory effect. In contrast, a long-term antimicrobial effect was present and more pronounced at higher concentrations of glycerol and higher temperatures of incubation. The mean survival time of Pseudomonas aeruginosa strains in glycerol 85% at 24 °C was 2.6 days, 14.7 days for the tested staphylococci and 29.6 days for three vegetative Bacillus species. In conclusion, microbial safety of glycerol-preserved skin can be increased by preserving skin allografts for some weeks at room temperature.