Sabine Poelzl

The survival of pathogenic microorganisms on surfaces is contingent on environmental factors, including humidity and temperature. In order to analyze the s

Bacteriophages can serve as practical surrogates for human viruses in laboratory tests. They share key structural characteristics but are non-pathogenic and can be handled under lower biosafety conditions. This facilitates experiments on persistence, disinfection and materials-testing while reducing time, costs and logistical requirements. However, phage survival strongly depends on many factors including environmental conditions, such as temperature and relative humidity (RH). This study investigates the survival of bacteriophages Phi6, Qbeta and MS2 under different incubation conditions including storage on a surface, in liquid and in the fridge. Standardized ISO protocols for antimicrobial surface testing and extensions were applied. All phages demonstrated good survival in liquid, although stability was temperature-dependent. At refrigerator temperatures, phages remained stable for several months with only minor reduction in the initial titer. At 50 °C, the two non-enveloped phages survived for up to one week, whereas the enveloped phage Phi6 was inactivated within one day. On glass surfaces, Phi6 exhibited reduced stability and was detectable only up to one week at 25 °C and >90% RH. Qbeta and MS2 survived from several days at 50 °C to two to seven days at 37 °C, depending on RH, and remained detectable at 25 °C regardless of humidity. These differences highlight the importance of carefully selecting incubation conditions, as these directly affect phage stability. In particular, unsuitable conditions for antimicrobial testing may cause phage inactivation and thus lead to false-positive results. Therefore, it is essential to define the conditions under which each phage produces reliable results.

Candidozyma auris—formerly known as Candida auris—is an emerging multidrug-resistant fungus causing life-threatening outbreaks, particularly in healthcare settings. Its ability to contaminate hospital equipment, persist on certain surfaces and develop resistance to commonly used antifungal agents makes it a critical priority pathogen. While classical hygiene measures are essential, increasing resistance to disinfectants calls for alternative approaches. One promising strategy is the use of antimicrobial materials on frequently touched surfaces to minimize the survival rate of problematic microorganisms. As literature does not provide a lot of data regarding the survival of Candida genera on surfaces, the present study was undertaken to analyze the survival/elimination of C. auris on different common and specific surfaces. ISO 22196:2011 was used to generate an overview of the efficacy of these surfaces against DSMZ strains of C. auris and C. albicans, respectively. The findings indicate that C. albicans can be regarded as suitable model organism for C. auris. Three clinical C. auris isolates with different genetic characteristics and/or phylogeographic origins yielded similar results to the DSMZ strains, providing a clear indication of the antifungal efficacy of surfaces tested. While reference materials without antimicrobial additives showed no efficacy, a combination of zinc and copper achieved the required 3 log₁₀ reduction after 24 h. Most effective against all fungal strains in two different types of tests was a layer of antimicrobial lacquer, which showed a significant decrease in fungal survival within 1 h. Thus, these surface modifications can be considered as effective tools for fighting C. auris in hygienically critical areas.

The application of antimicrobial surfaces requires proof of their effectivity by in vitro methods in laboratories. One of the most common test methods is ISO 22196:2011, which represents a simple and inexpensive protocol by applying the bacterial suspension with known volume and concentration covered under a polyethylene film on the surfaces. The incubation is then conducted under defined humidity conditions for 24 h. Another approach for testing non-porous surfaces is the newly published ISO 7581:2023. With this protocol, a “dry test” is achieved by spreading and drying 1 μL of a bacterial suspension on the surfaces. A comprehensive evaluation of both standard protocols was conducted. This showed that they have some limitations and often do not include realistic test conditions that refer to the final product. Accordingly, the objective of this study was to develop a novel testing procedure that uses the spraying of a suspension inside of a chamber to generate aerosols with a precisely defined bacterial or yeast load. The samples to be analyzed are covered with small droplets that dry up within a few minutes and thus enable very reproducible contamination of the surfaces. The test series was carried out with low-alloyed carbon steel and glass without antimicrobial substances against two different Escherichia coli and Staphylococcus epidermidis strains and one Candida albicans strain to evaluate the new method. The results provided reproducible and reliable results in the setup carried out. This test method represents a valuable alternative for the assessment of non-porous surfaces in a manner that more closely reflects real-world conditions (e.g., simulation of aerosol formation by sneezing).

One of the greatest challenges worldwide is containing the spread of problematic microorganisms. A promising approach is the use of antimicrobial coatings (AMCs). The antimicrobial potential of certain metals, including copper and zinc, has already been verified. In this study, polyethylene terephthalate and aluminum (PET-Al) foils were coated with copper, zinc, and a combination of these two metals, known as core–shell particles, respectively. The resistance of the three different types of coatings to mechanical and chemical exposure was evaluated in various ways. Further, the bacteria Staphylococcus aureus and the bacteriophage ϕ6 were used to assess the antimicrobial efficacy of the coatings. The best efficacy was achieved with the pure copper coating, which was not convincing in the abrasion tests. The result was a considerable loss of copper particles on the surfaces and reduced effectiveness against the microorganisms. The core–shell particles demonstrated better adhesion to the surfaces after abrasion tests and against most chemical agents. In addition, the antimicrobial efficiency remained more stable after the washability treatment. Thus, the core–shell particles had several benefits over the pure copper and zinc coatings. In addition, the best core–shell loading for durability and efficacy was determined in this study.

The application of antimicrobial surfaces requires the proof of their effectivity by in vitro methods in laboratories. One of the most well-known test methods is ISO 22196:2011, which represents a simple and inexpensive protocol by applying the bacterial suspension with known volume and concentration covered under a polyethylene film on the surfaces. The incubation is then done under defined humidity conditions for 24 h. Another approach for testing of non-porous surfaces is the newly published ISO 7581:2023. A “dry test” is achieved through spreading and drying 1 μL of a bacterial suspension on the surface. In this study, low alloyed carbon steel, polyethylene terephthalate (PET), and glass specimens were tested uncoated (reference) and coated with zinc according to both ISOs to compare and to evaluate the advantages and disadvantages of each one of them. Although ISO 7581:2023 allows a more realistic test environment than ISO 22196:2011, the reproducibility of the results is not given due to the low application volume. In addition, not all bacterial strains are equally suitable for this testing type. Individual adaptations to the protocols, including incubation conditions (time, temperature, or relative humidity), testing strains and volume, seem necessary to generate conditions that simulate the final application. Nevertheless, both ISOs, if used correctly, provide a good basis for estimating the antimicrobial efficacy of non-porous surfaces.

Due to the COVID-19 pandemic, researchers have focused on new preventive measures to limit the spread of SARS-CoV-2. One promising application is the usage of antimicrobial materials on often-touched surfaces to reduce the load of infectious virus particles. Since tests with in vitro-propagated SARS-CoV-2 require biosafety level 3 (BSL-3) laboratories with limited capacities and high costs, experiments with an appropriate surrogate like the bacteriophage ɸ6 are preferred in most studies. The aim of this study was to compare ɸ6 and SARS-CoV-2 within antiviral surface tests. Different concentrations of copper coatings on polyethylene terephthalate (PET) were used to determine their neutralizing activity against ɸ6 and SARS-CoV-2. The incubation on the different specimens led to similar inactivation of both SARS-CoV-2 and ɸ6. After 24 h, no infectious virus particles were evident on any of the tested samples. Shorter incubation periods on specimens with high copper concentrations also showed a complete inactivation. In contrast, the uncoated PET foils resulted only in a negligible reduced inactivation during the one-hour incubation. The similar reduction rate for ɸ6 and SARS-CoV-2 in our experiments provide further evidence that the bacteriophage ɸ6 is an adequate model organism for SARS-CoV-2 for this type of testing.

The versatility of sol–gel systems makes them ideal for functional coatings in industry. However, existing coatings are either too thin or take too long to cure. To address these issues, this paper proposes using an atmospheric pressure plasma source to fully cure and functionalize thicker sol–gel coatings in a single step. The study explores coating various substrates with sol–gel layers to make them scratch-resistant, antibacterial, and antiadhesive. Microparticles like copper, zinc, or copper flakes are added to achieve antibacterial effects. The sol–gel system can be sprayed on and quickly functionalized on the substrate. The study focuses on introducing and anchoring particles in the sol–gel layer to achieve an excellent antibacterial effect by changing the penetration depth. Overall, this method offers a more efficient and effective approach to sol–gel coatings for industrial applications. In order to achieve a layer thickness of more than 100 µm, the second part of the study proposes a multilayer system comprising 15 to 30 µm thick monolayers that can be modified by introducing fillers (such as TiO₂) or scratch-resistant chemicals like titanium isopropoxide. This system also allows for individual plasma functionalization of each sol–gel layer. For instance, the top layer can be introduced with antibacterial particles, while another layer can be enhanced with fillers to increase wear resistance. The study reveals the varying antibacterial effects of spherical particles versus flat flakes and the different scratch hardnesses induced by changes in pH, number of layers, and particle introduction.

Understanding interactions of bacteria with fiber-based packaging materials is fundamental for appropriate food packaging. We propose a laboratory model to evaluate microbial growth and survival in liquid media solely consisting of packaging materials with different fiber types. We evaluated food contaminating species (Escherichia coli, Staphylococcus aureus, Bacillus cereus), two packaging material isolates and bacterial endospores for their growth abilities. Growth capacities differed substantially between the samples as well as between bacterial strains. Growth and survival were strongest for the packaging material entirely made of recycled fibers (secondary food packaging) with up to 10.8 log₁₀ CFU/ml for the packaging isolates. Among the food contaminating species, B. cereus and E. coli could grow in the sample of entirely recycled fibers with maxima of 6.1 log₁₀ and 8.6 log₁₀ CFU/mL, respectively. Escherichia coli was the only species that was able to grow in bleached fresh fibers up to 7.0 log₁₀ CFU/mL. Staphylococcus aureus perished in all samples and was undetectable after 1–6 days after inoculation, depending on the sample. The packaging material strains were isolated from recycled fibers and could grow only in samples containing recycled fibers, indicating an adaption to this environment. Spores germinated only in the completely recycled sample. Additionally, microbial digestion of cellulose and xylan might not be a crucial factor for growth. This is the first study describing bacterial growth in food packaging materials itself and proposing functionalization strategies toward active food packaging through pH-lowering.