Incorporating zinc oxide nanoparticles (ZnO NPs) into cement mortars may provide additional functions, e.g., self-cleaning and antibacterial or electroconductive ability. However, these NPs are also known for their potential toxicity. During the life cycle of a cement mortar, various abrasive forces cause the release of admixtures to the natural environment. The effect of the released NPs on model microorganisms has not been extensively studied. Previous studies have shown that nanomaterials may affect various microorganisms’ physiological responses, including changes in metabolic activity, biofilming, or growth rate. In this study, we have focused on evaluating the response of model microorganisms, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans, towards ZnO nanoparticles released from cement mortars in different deterioration scenarios. The addition of ZnO nanoparticles to cement mortars had a noticeable effect on impeding the strength development. We have also detected that depending on the deterioration scenario, the release of ZnO nanoparticles was varied. Our studies have also shown that even though the release of nanoform ZnO could be limited by poor dispersion or the used filtration technique, the eluates have caused slight but statistically significant changes in the physiological features of studied microorganisms showing relatively low toxicity.

Pseudomonas aeruginosa is a bacterium of high clinical and biotechnological importance thanks to its high adaptability to environmental conditions. The increasing incidence of antibiotic-resistant strains has created a need for alternative methods to increase the chance of recovery in infected patients. Various nanomaterials have the potential to be used for this purpose. Therefore, we aimed to study the physiological response of P. aeruginosa PAO1 to titanium dioxide/silica nanotubes. The results suggest that UV light-irradiated nanomaterial triggers strong agglomeration in the studied bacteria that was confirmed by microscopy, spectrophotometry, and flow cytometry. The effect was diminished when the nanomaterial was applied without initial irradiation, with UV light indicating that the creation of reactive oxygen species could play a role in this phenomenon. The nanocomposite also affected biofilm formation ability. Even though the biomass of biofilms was comparable, the viability of cells in biofilms was upregulated in 48-hour biofilms. Furthermore, from six selected genes, the mexA coding efflux pump was upregulated, which could be associated with an interaction with TiO2. The results show that titanium dioxide/silica nanotubes may alter the physiological and metabolic functions of P. aeruginosa PAO1.

The research carried out so far for phage-antibiotic synergy (PAS) differs as regards the technique of modifying the double-layer agar (DLA) method to show the PAS effect on Petri plates, which may contribute to non-uniform research results. Therefore, there is a need to unify the method to effectively detect the PAS effect, at its most basic in vitro test. In this study, bacteriophage T45 and 43 antibiotics belonging to different antibiotic classes were used. Seven different DLA method modifications were tested, in terms of antibiotic addition placement and presence or absence of the base agar. The overall number of phage plaques per plate mainly depended on the antibiotic used. Differences in plaque quantity depended on the type of the DLA method modification. The largest total number of plaques was obtained by the addition of an antibiotic to a bottom agar with the presence of a top agar. This indicates that even though an antibiotic could manifest the PAS effect by a standard disk method, it would be worth examining if the effect is equally satisfactory when applying antibiotics directly into the agar, with regards to using the same bacteriophage and bacterial host.

Building materials are constantly improved with various additives and admixtures in order to achieve goals ranging from obtaining increased durability or antimicrobial activity up to reducing the carbon footprint left by the cement production. Since nanomaterials were proposed for cement products, many studies explored the possibilities for their incorporation. One of the novel trends in studying these materials is evaluating their impact on living organisms, with the focus not only on toxicology but also on the application potential. Therefore, in this study, we investigated the effects of three types of calciumsilicate-hydrate (C-S-H) seeds on reference microorganisms in the scope of their basic physiology and primary metabolism. Shape, size and elemental composition of C-S-H seeds were also evaluated. The tests on the reference microorganisms have shown that the reaction to these nanomaterials can be specific and depends on the strain as well as the type of used nanomaterial. Furthermore, the presence of C-S-H seeds in the growth environment led to metabolic stimulation that resulted in faster growth, higher biochemical activity, and increased biofilm formation. Based on our findings, we conclude that even though C-S-H seeds have antimicrobial potential, they can be potentially used to promote the growth of selected microbial strains. This phenomenon could be further investigated towards the formation of beneficial biofilms on building materials.

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Pseudomonas aeruginosa is a bacterium producing industrially utile metabolites, such as rhamnolipids, biopolymers, and pigments. Pyocyanin, the most studied example of pigments, is a virulence factor that also shows the potential for application in, e.g., agriculture, anticancer therapy, and energy production. Therefore, potential inhibitors and stimulants of pyocyanin production by P. aeruginosa should be studied, and nanomaterials may cause both effects. The study aimed to examine the influence of zinc oxide and multi-walled carbon nanotubes (pristine or dispersed with alginic acid) on pyocyanin production by P. aeruginosa. First, the influence of different concentrations of nanomaterials (500.00–0.06 µg/mL) on culture optical density and biofilm formation was studied. These results helped select concentrations for further tests, i.e., growth curves and fluorescence measurements. Pyocyanin production was assessed by the chloroform–hydrochloric acid method. SEM analysis was conducted to assess the influence of nanomaterials on the cell's integrity and biofilm structure. Pristine multi-walled carbon nanotubes exhibited a stimulative effect on pigment production when applied in high concentrations (500.00 µg/mL), while dispersed material enhanced the production in lowered dosages (125.00 µg/mL). On the other hand, high concentrations of zinc oxide inhibited pyocyanin production, while minor increased bioproduct production. The research indicates the potential to use nanomaterials as the modulators of pyocyanin production and other metabolites.

The ambiguous nature of pyocyanin was noted quite early after its discovery. This substance is a recognized Pseudomonas aeruginosa virulence factor that causes problems in cystic fibrosis, wound healing, and microbiologically induced corrosion. However, it can also be a potent chemical with potential use in a wide variety of technologies and applications, e.g. green energy production in microbial fuel cells, biocontrol in agriculture, therapy in medicine, or environmental protection. In this mini-review, we shortly describe the properties of pyocyanin, its role in the physiology of Pseudomonas and show the ever-growing interest in it. We also summarize the possible ways of modulating pyocyanin production. We underline different approaches of the researchers that aim either at lowering or increasing pyocyanin production by using different culturing methods, chemical additives, physical factors (e.g. electromagnetic field), or genetic engineering techniques. The review aims to present the ambiguous character of pyocyanin, underline its potential, and signalize the possible further research directions.