Epseptimavirus KKP3831 - a new species of Salmonella-specific virulent phage: comprehensive biological and genomic characterization and potential for translocation through the intestinal epithelium.

Salmonella, an etiological agent of salmonellosis, is one of the main foodborne pathogens. Due to irrational antibiotic stewardship, an increase in the incidence of multidrug resistance (MDR) in bacteria has been observed recently. Phage therapy represents an alternative method of treating infections, including foodborne pathogens. Therefore, this study aimed to isolate and comprehensively characterize a bacteriophage specific for MDR Salmonella enterica strain KKP 998, isolated from the food environment. Transmission electron microscopy (TEM) and whole-genome sequencing (WGS) analyses classified the identified phage as a member of the tailed phages from Epseptimavirus genus and Caudoviricetes class. Neither antibiotic resistance genes, toxin genes, nor genes associated with host genome integration (markers of temperate bacteriophages) were located in the phage genome. A newly isolated bacteriophage, Epseptimavirus KKP3831 (Salmonella phage KKP_3831), replicated in multiple serovars of S. enterica hosts. Active progeny particles were produced in 50 % of the S. enterica strains tested, indicating partial host specificity. Epseptimavirus KKP3831 can translocate through the Caco-2 monolayer in both directions, apical-to-basal and basal-to-apical, in a clearly dose-dependent manner and only subtly dependent on incubation time. The strictly lytic nature of replication and favorable physiological parameters (short latent period (20 min) and medium burst size (42 ± 4 PFU/cell)) suggest that Epseptimavirus KKP3831 is a promising candidate for biocontrol and treatment of salmonellosis caused by MDR S. enterica strains. The potential for translocation across the intestinal epithelium highlights the importance of studying the mechanisms of phage circulation in the body, as well as their effects beyond the site of administration, beyond just their antibacterial action.