Salmonella phage characterization and host-dependent responses relevant to cocktail formulation

This study was characterized infection efficiency, replication kinetics, environmental tolerance, and host-associated responses of six Salmonella phages (Yrd1, Yrd2, NB1, NB2, NB3, and FPU) as candidate parameters relevant to cocktail formulation. All phages belong to the class Caudoviricetes, comprising five myovirus-like and one siphovirus-like (NB3) morphotype, with capsid dimensions of 38-74 nm in width and 46-94 nm in length, and tail lengths of 78-109 nm. Multiplicity of infection (MOI) assays (0.001-10) showed that low MOI conditions (0.001-0.01) produced higher phage amplification, whereas a high MOI (10) markedly reduced amplification, indicating reduced infection efficiency at higher phage-to-host ratios. One-step growth analysis (MOI 0.1) showed phage-specific latent periods ranging from 10 to 30 min. Burst size ranged from 15 to 389 PFU/cell, with Yrd2 and NB1 showing the two highest values. Stability assays showed phage-specific responses. FPU displayed the broadest pH tolerance profile in the plotted comparison, retaining normalized infectivity from pH 5 to 10, and showed the highest plotted normalized infectivity at 50-60^OC. All six phages showed near-zero normalized infectivity at pH 2-3, pH 11-12, and 70^OC. Network-based interaction analysis showed broader OD-based inhibitory connectivity for selected cocktails than for monophages across PU13036, EN, KE, and TY. On PU519, specific FPU-containing combinations showed reduced inhibition, but these effects are not interpreted as mechanistic phage-phage antagonism or generalized beyond the tested host. Because the assays used different host backgrounds, these measurements provide candidate parameters for future cocktail-selection studies, but their predictive value requires further validation.