Isolation and Characterization of Salmonella Bacteriophages

Numerous foodborne infections and outbreaks are associated with Salmonella which makes it a challenge in terms of human health and economy. Therefore, reducing the prevalence of Salmonella in food and food processing areas is of great importance. Antibiotics are the substances that are commonly used in various stages of food production in order to fight against Salmonella. However, concerns related with the antibiotic use like antibiotic resistance give rise to pursuit of safer methods to eliminate Salmonella from the environment. Bacteriophages (phages) are seen as promising tools for the control of bacteria as they are viruses that use bacterial cells as their hosts. Nonetheless, their characteristics must be well-defined in order to get GRAS status and be used in industry. Additionally, since the distribution of Salmonella serovars varies geographically, regional effects are also important in phage-based applications. For this reason, bacteriophage cocktails designed in other countries may not show sufficient effect against isolates in Turkey. Current study aims to isolate and characterize Salmonella bacteriophages from cattle-poultry feces coming from distinct regions in Turkey and from wastewater in order to find an alternative to antibiotics. In total 25 Salmonella bacteriophages were isolated. The most abundant phages were against S. Enteritidis and other than that S. Typhimurium, S. Kentucky, S. Hadar, S. Telaviv and S. Anatum phages were obtained. In the next step, titers and host ranges of these bacteriophages were determined. Host range analysis revealed the differences in phage lysing capabilities of bacteriophages and showed that phages isolated from wastewater had broader host ranges compared to the phages obtained from feces. The phage with the broadest host range was defined as the phage whose indicator strain was S. Telaviv and it was capable of infecting 77.7% of the serovars partially or totally. Moreover, bacteriophages was subjected to single step growth curve experiments in order to determine their burst size and latent periods which are important parameters for their use in phage cocktails. Phage P1-224 exhibited the greater burst size (236 PFU/cell) with short latent period (15 min) among others. Bacteriophages were also subjected to Pulsed Field Gel Electrophoresis (PFGE) to determine their genome size. Isolated phages genome sizes were in the range of 33- 124 kb. Besides, Salmonella isolation was performed from the collected samples. In total 4 Salmonella strains were isolated. Their subtyping was conducted by PFGE analysis. As a result, 2 S. Enteritidis and 2 S. Typhimurium were identified. This study provided a better understanding of phage-host interactions and diversities in phages nature which possess significant importance for their use in food safety applications.


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Citation Formats
A. DENİZ, “Isolation and Characterization of Salmonella Bacteriophages,” M.S. - Master of Science, Middle East Technical University, 2022.