Salmonella Spp. ve Escherıchıa colı’ye Etkili Bakteriyofajların Karakterizasyonu ve Gıda Uygulamaları

Abstract

There are many biological and chemical methods to combat with foodborne pathogens. Improvements or alternatives are required about the use of antimicrobial chemicals, namely antibiotics, due to the acceleration of the emergence of antibiotic-resistant bacteria. Salmonella species are pathogenic bacteria that cause foodborne infections and have serious health effects, as well as induce food spoilage. Escherichia coli(E. coli) which passed foods via problems such as contamination, insufficient heat treatment causes spoilages. Phage therapy is used as a biological control method for the elimination of these bacteria. In this thesis, bacteriophages effective against E. coli K-12 were isolated, purified and concentrated. Host ranges of bacteriophages were determined and their adsorption rate constants were calculated. DNA isolation of concentrated bacteriophages was performed and these DNAs were used to obtain fragment templates by digesting with restriction enzymes. One-step growth curves of bacteriophages, which were found to be different according to this method, were inferred, burst size and latent periods were determined. Moreover, pH and temperature stability are determined. Concentrated phages were also morphologically characterized by transmission electron microscopy. Inhibition of S. enteritidis, S. typhimurium and E. coli K-12 bacteria in skimmed milk was tested using bacteriophage mixtures effective against host bacteria. These experiments were carried out at different ambient temperatures (4 and 25°C) and different bacterial inoculation amounts. At the end of 24 hours, the highest bacterial inactivation was detected at low bacterial inoculation amounts as 3.5 log10 CFU/ml for Salmonella phage mix and 4.8 log10 CFU/ml for E. coli K-12 phage mix at 25°C. In order to simulate the breaking of the cold chain, the milks of the control group containing E. coli K-12 and the experimental group milks to which a mixture of bacteriophages with different MOIs were stored at 4°C for 7 days. At the end of 7 days, the milk samples were incubated at 25°C and the changes in bacteria or bacteriophage numbers were followed for 24 hours. The effect of the presence of stress on bacteriophage therapy in E. coli K-12 inactivation in milk was demonstrated for the first time with this study. Within the scope of the thesis, the effect of environmental parameters in the application of bacteriophage mixture to skimmed milk was investigated and it was concluded that these mixtures could be used in the biocontrol of Salmonella and E. coli K-12 bacteria.