Nanocomposites and nanomaterials

Microbiological evaluation of metal oxide nanoparticles 
Augustyniak A.1, Sikora P.2,3, Cendrowski K.4, Mijowska E.4, Stephan D.3
1 Department of Immunology, Microbiology and Physiological Chemistry, Faculty of Biotechnology and Animal Husbandry, West Pomeranian University of Technology, Szczecin. Al. Piastow 45, 70-311 Szczecin, Poland
2 Faculty of Civil Engineering and Architecture, West Pomeranian University of Technology, Szczecin. Al. Piastow 50, 70-311 Szczecin, Poland
E-mail: pawel.sikora@zut.edu.pl
3 Building Materials and Construction Chemistry, Technische Universität Berlin, Gustav-Meyer-Allee 25, 13355 Berlin, Germany
4 Nanomaterials Physicochemistry Department, Faculty of Chemical Technology and Engineering, West Pomeranian University of Technology, Szczecin. Al. Piastow 45, 70-311 Szczecin, Poland
Nanomaterials are versatile substances that are often used as antimicrobial agents. Such application was proposed, e.g., for cementitious materials. Nevertheless, their action depends on several factors such as composition, surface area or aggregation tendency. 
In our study Al2O3, CuO, Fe3O4, and ZnO nanoparticles were used and tested on reference strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Nanomaterials were used in a way corresponding to standard procedures used in the preparation of cementitious composites. Morphology and viability of cells were tested with microscopy, spectrophotometry, and culture methods.
The results revealed that nanoparticles may lose their antimicrobial efficiency, possibly due to the aggregation process. Even though studied particles were toxic to subject microorganisms in acute tests, the populations were able to re-grow when co-incubated with the nanoparticles in liquid medium. Furthermore, we found a considerable diversity in the reaction of tested strains to nanoparticles, even between four different strains of Escherichia coli.
Our findings indicate that there is a necessity to optimize evaluation methods, especially in the direction of choosing suitable test strains and approach consistent with the further application of nanomaterials. This would ensure reliable results covering possible variations between genera and strains. 
Acknowledgement: This research was supported by the National Science Centre within the project No. 2016/21/N/ST8/00095 (PRELUDIUM 11).