Vorobiei Y. Biological aspect of the action of bacteriophages on biofilms, formed by Staphylococcus aureus

Thesis for PhD degree in Biology (specialty 03.00.07 – «Microbiology». – Oles Honchar Dnipro National University, D.K. Zabolotny Institute of Microbiology and Virology of the NASU, Kyiv, 2018. The dissertation is devoted to the study of the aspects of the interaction of bacteriophages with biofilms and the development of methods for the destruction of bacterial biofilms with the help of bacteriophages in medicine. For the first time quantitative parameters of growth of S. aureus biofilms and their changes under conditions of phage influence were obtained. The greatest increase in CFU was observed during the first day of incubation, when there was an intensive fission of staphylococcus cells. At the same time, the maximum increase in the optical density of films was observed on the second and third day of incubation, when the accumulation of a polymer matrix around the cells began. When studying the effect of bacteriophage preparations on the process of film formation, it was shown that phage preparations resulted in decrease in the researched parameters when placing films at all stages of incubation. It was shown that the maximum suppressive effect on the growth of biofilms in the application of therapeutic preparations of bacteriophages was shown when applied per day (for the drug «Piobacteriophage polyvalent») and a two-day biofilm (for the preparations «Bacteriophage staphylococcal liquid» and «Intesti-bacteriophage liquid»). The ratio of the components of the exopolymer matrix of Staphylococcus aureus microfilms was determined and for the first time the dependence between the chemical composition of the matrix and the sensitivity of the biofilms to the phages was shown. Added to this is the fact that the dependence of the intensity of the bacteriophage preparations effects on the films of the investigated S. aureus strains on the concentration of exopolysaccharides in the framework of their matrix was proved. Specifically, the greatest destructive influence was found for sodium periodate (a decrease in the optical density of the film by 59.02% in comparison with the control of untreated film), and, consequently, the highest content of exopolysaccharides in the framework of matrix coincided with the greatest influence of therapeutic preparations of bacteriophages on films (decrease in optical density by 41.40%). Whereas the least influence of sodium periodate on existing films (decrease in optical density by 47.00%) coincided with the least influence of bacteriophage preparations (decrease in optical density by 32.70%). For the first time an effective scheme of correctional effects of phage preparations in conjunction with the probiotic drug «Vagilak» for the vaginal dysbiosis of white laboratory mice, caused by intravaginal administration of biofilm and non-biofilm strains S. aureus, was developed. Thus, it must be taken into account, that the use of only bacteriophage preparations did not show a complete renovation of the normoflora of the vaginal biotope. They destroyed potentially pathogenic bacteria, against which they were directed, without causing significant changes in other microorganisms. However, in combination with a probiotic, all the used bacteriophages resulted in almost complete recovery of the microflora status. Summarizing data provided above, it may be deduced that the therapeutic preparations of bacteriophages show activity against staphylococcal films in vitro and staphylococci which are capable of forming films in vivo, so it is advisable to use them in medical practice for treating lesions of any location both independently and in combination with other means.