Süt ve Süt Ürünlerinde Sorunlara Neden Olan Patojen Salmonella SPP. ve Psikrotrof Pseudomonas Fluorescens Suşlarının Biyokontrolünde Bakteriyofajların Kullanımı

Abstract

Salmonella spp. and psychrotrophic microorganisms are significant concerns in the dairy industry. Salmonella, a prominent foodborne pathogen, poses substantial health risks and remains a global public health concern. Conversely, strains belonging to the Pseudomonas fluorescens complex exhibit psychrotrophic characteristics and are primarily found in refrigerated milk. These bacteria are notable for their production of extracellular enzymes, which can retain their activity even after thermal processing. Consequently, this enzymatic activity can lead to detrimental effects such as a reduction in the shelf life of pasteurized-UHT milk and dairy products, gelation, and flavor deterioration. Therefore, the presence and management of these microorganisms are crucial considerations in maintaining food safety and ensuring the quality of dairy products. Bacteriophages are viruses that specifically infect bacteria and emerge as an important alternative in combating pathogenic/spoilage bacteria in food, achieving success in many applications. The aim of this study was to isolate, identify, and comprehensively characterize relevant bacteriophages from various sources for the biocontrol of these bacteria causing problems in the dairy industry, and to determine the effectiveness of phage cocktails in milk. For this purpose, bacteria and bacteriophage isolation was first carried out. During the characterization of bacteriophages, the host range was initially determined, revealing a high degree of host specificity for both Salmonella and Pseudomonas fluorescens phages. Subsequent analysis utilizing transmission electron microscopy images allowed for the identification of the morphotypes of these phages. It was observed that Salmonella phages exhibited siphovirus and myovirus morphotypes, whereas Pseudomonas phages demonstrated siphovirus and tectivirus. Restriction fragment length polymorphism analysis was used to classify the bacteriophages. Subsequently, one-step growth and adsorption curves were obtained to determine the replication parameters of the bacteriophages and it was found that the latent period of Salmonella phages ranged from 5 to 25 min, and the burst sizes ranged from 42 to 176 plaque-forming units (PFU) per cell. For Pseudomonas bacteriophages, the latent periods ranged from 5 to 15 min, and the burst sizes ranged from 10 to 91 PFU per cell. Partial sequence analysis of Salmonella phages revealed the absence of toxic gene regions. Additionally, the complete genome analysis was performed for three Pseudomonas phages, and it was discovered that one of them was a new bacteriophage which was not found in the GenBank database. Following the characterization, the effectiveness of bacteriophage cocktails was demonstrated in milk. For Salmonella, a bacterial reduction up to 1.01 log units was achieved, while for Pseudomonas, reductions up to 5.29 log units in UHT milk and 3.44 log units in raw milk were obtained. In the raw milk experiment conducted with the Pseudomonas spp., the impact of phages on other dominant microorganism groups and the physical and chemical properties of milk were also examined. The studies revealed that bacteriophages could control the target microorganism group without significantly affecting the pH, titratable acidity, color, and other properties of milk in different types and compositions. This research contributes to addressing the existing gaps in the literature, providing a contemporary and innovative approach for the natural and cost-effective resolution of challenges in the dairy industry that cannot be adequately addressed by current methods in both Turkey and globally.