Antimicrobial effect of colloid solutions of nanoparticles of elementary metals and metallic oxides on MSSA and MRSA

Smanjivanjem veličine čestica vrlo često se mijenjaju fizikalno-kemijska svojstva, pogotovo ako se veličina čestica smanji na dimenzije ispod 1 μm. Smanjivanjem veličine čestica ispod 1 μm otvara se mogućnost pronalaska novih biološki aktivnih tvari. Jedne od takvih biološki aktivnih tvari su nanočestice metala i metalnih oksida (MNP), te je cilj ovog rada istražiti antimikrobna svojstva MNP u koloidnom obliku. Koloidni MNP pokazuju vrijednosti minimalne baktericidne (MBK) i inhibitorne (MIK) koncentracije u rasponima od 0,01 do 100 ppm-a. Najniže MIK i MBK vrijednosti pokazuju nanočestica koloidnog ZnO, dok najviše pokazuju nanočestice koloidnog TiO2, međutim koloidne nanočestice ZrO2 pokazuju bakteriostatski učinak u cijelom rasponu ispitivanih koncentracija, dok baktericidni učinak izostaje. Pokazano je da i antimikrobnu učinkovitost koloida Ag mogu smanjivati kompleksni mediji, kao što su serum te otopine proteina. Iako MNP djeluju uglavnom na nespecifičan način, preko tvorbe reaktivnih kisikovih vrsta (ROS) i penetracija membrane, odnosno stijenke, postoje značajne razlike među meticilin-rezistentnom (MRSA) i meticilin-osjetljivom (MSSA) soju vrste Staphylococcus aureus. Sinergizam nanočestica se ispitivao putem indeksa frakcionarne baktericidne (FBKI), odnosno inhibitorne (FIKI) koncentracije, te tako kombinacije koloidnog Ag, ZnO, i TiO2, na soju MRSA pokazuju sinergistički, a na soju MSSA antagonistički učinak. U svrhu ispitivanja praktične primjene MNP, tkanina od 1cm2 impregnirala se slojem smjese koloida MNP te se ispitivala njena antimikrobna učinkovitost u vremenu pomoću „time-kill“ metode. Potpuna redukcija vijabilnih bakterija soja MSSA i MRSA postignuta je nakon 18 sati, s time da je redukcija soja MRSA brža nego soja MSSA.Reducing the size of particles results in different physical and chemical properties, especially if the size is reduced below 1 μm. Reducing the size of particles below 1 μm opens up the possibility of finding new biologically active compounds. One of such biologically active compunds are nanoparticles of metals and metalic oxides (MNP), and therefore it is the cause of this paper to explore antimicrobial properties of MNP in colloid form. Colloid MNP show minimal bactericidal (MBC) and inhibitory (MIC) concentrations in ranges of 0,01 to 100 ppm. Lowest MIC and MBC values belong to colloid NP of ZnO, while highest values belong to colloid TiO2, however, colloid nanoparticles of ZrO2 demonstrate bacteriostatic effect in the entire range of tested concentrations, while bactericidal effect is absent. It has also been shown that antimicrobial efficacy of colloid Ag can be reduced by complex mediums, such as serum and protein solutions. Although MNP act through unspecific pathways, such as generations of reactive oxygen species (ROS) and penetration of cell membrane and wall, there are significant differences between methicillin-resistent (MRSA) and methicillin-sensitive (MSSA) strains of Staphyloccocus aureus. Synergism of nanoparticles was tested through fractionary bactericidal (FBCI) and inhibitory (FICI) concentration index, and combinations of colloid Ag, ZnO, and TiO2 show synergystic effect on MRSA, and antagonistic effect on MSSA. In the effort to test practical usage of MNP, a fabric of 1cm2 was impregnated with a layer of mixture of colloid MNP, and had its antimicrobial efficacy in time tested using „time-kill“ assay. Complete reduction of viable bacteria of strains MSSA and MRSA was achieved after 18 hours, with the fact that reduction of MRSA strain was faster than MSSA strain