Isolation of bacteriophages active on the clinical isolates of Enterococcus spp.from the environment and their characterization

Author: Teona Kheladze
Keywords: Enterococcus, VRE, Bacteriophages, Phage therapy
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Enterococcus is one of the most common cause of nosocomial infections. Their adaptability to hospital environment stems from their ability to survive harsh conditions. Moreover, they show intrusive resistance to commonly used antibiotics such as beta-lactams and aminoglycosides; They easily acquire resistance to other antimicrobial agents, such as the glycopeptide vancomycin. A patient infected with vancomycin-resistant Enterococcus faecium is very difficult and sometimes even impossible to cure. Although research is actively being conducted to discover and synthesize new antibiotics, there is a risk, that after some time, bacteria will develop resistance to these new agents as well. Therefore, it is advisable to improve such alternative methods of treatment as phage therapy. The aim of the research was isolation of bacteriophages active on the clinical isolates of Enterococcus spp. from the environment and their characterization. All the obtained nineteen clinical isolates were identified as enterococci using the following methods: Gram staining, bile esculin test and catalase test. Using a Mannitol Salt Agar, it was shown that six of the isolates are E. faecium, remaining thirteen - E. faecalis. Only two (E. faecium 10 and E. faecalis 61) strains showed resistance to antibiotics other than ampicillin. It was seen on the microplate method, that sixteen out of these nineteen stains form biofilms. Particularly strong biofilms were produced by five strains: E. faecalis 9, E. faecium 10, E. faecium 71, E. faecalis 86 & E. faecalis 90. Two bacteriophages (φ1 and φ6) were isolated from river Mtkvari and White Lake against clinical isolates of enterococci and their characteristics were studied. By electron microscopy it was shown that they represent the Siphoviridae morphological group. Using the streak method, it was determined, that phage φ1 has stronger activity even at lower dilutions. Moreover, φ1 is active on one of the multidrug-resistant strains (E. faecium 10). Both bacteriophages (φ1 and φ6) are stable in the temperature range of 4℃-55℃ during 1.5 h incubation. In the same period, the titre of both phages significantly decreases at 65℃ and becomes zero at 70℃. The best conditions for both phages are pH7 and weakly alkaline environment. φ6 is relatively resistant to different variations of both temperature and pH. Despite the morphological similarity, the isolated and studied phages show individual properties both in terms of activity against enterococcal strains and resistance to environmental factors. Further research is required to confirm the phenotypic difference at the genetic level.