Two Phages of the Genera Felixunavirus Subjected to 12 Hour Challenge on Salmonella Infantis Showed Distinct Genotypic and Phenotypic Changes

Abstract

Salmonella Infantis is considered in recent years an emerging Salmonella serovar, as it has been associated with several outbreaks and multidrug resistance phenotypes. Phages appear as a possible alternative strategy to control Salmonella Infantis (SI). The aims of this work were to characterize two phages of the Felixounavirus genus, isolated using the same strain of SI, and to expose them to interact in challenge assays to identify genetic and phenotypic changes generated from these interactions. These two phages have a shared nucleotide identity of 97% and are differentiated by their host range: one phage has a wide host range (lysing 14 serovars), and the other has a narrow host range (lysing 6 serovars). During the 12 h challenge we compared: (1) optical density of SI, (2) proportion of SI survivors from phage-infected cultures, and (3) phage titer. Isolates obtained through the assays were evaluated by efficiency of plating (EOP) and by host-range characterization. Genomic modifications were characterized by evaluation of single nucleotide polymorphisms (SNPs). The optical density (600 nm) of phage-infected SI decreased, as compared to the uninfected control, by an average of 0.7 for SI infected with the wide-host-range (WHR) phage and by 0.3 for SI infected with the narrow-host-range (NHR) phage. WHR phage reached higher phage titer (7 × 1011 PFU/mL), and a lower proportion of SI survivor was obtained from the challenge assay. In SI that interacted with phages, we identified SNPs in two genes (rfaK and rfaB), which are both involved in lipopolysaccharide (LPS) polymerization. Therefore, mutations that could impact potential phage receptors on the host surface were selected by lytic phage exposure. This work demonstrates that the interaction of Salmonella phages (WHR and NHR) with SI for 12 h in vitro leads to emergence of new phenotypic and genotypic traits in both phage and host. This information is crucial for the rational design of phage-based control strategies.

Analysis of Selection Methods to Develop Novel Phage Therapy Cocktails Against Antimicrobial Resistant Clinical Isolates of Bacteria

“…These three tests form the basis for the initial screening of a phage library to identify phages with the broadest host range. The data generated also allowed direct comparison of DST versus EOP, as these two assays are commonly used to characterise phages ( Sybesma et al, 2016 ; Montso et al, 2019 ; Rivera et al, 2019 ; Supplementary Tables S5 , S6 ).…”

Analysis of selection methods to develop novel phage therapy cocktails against antimicrobial resistant clinical isolates of bacteria

“…These three tests form the basis for the initial screening of a phage library to identify phages with the broadest host range. The data generated also allowed direct comparison of DST versus EOP, as these two assays are commonly used to characterise phages (Montso et al, 2019; Rivera et al, 2019; Sybesma et al, 2016) [Supplementary Data Table S5 & S6].…”

Exploring the Remarkable Diversity of Culturable Escherichia coli Phages in the Danish Wastewater Environment

“…In this study, felixounaviruses were identified 33 times in samples from no less than 23 WWTPs, indicating that they are ubiquitous in the Danish wastewater environment and that they are easily cultivated, though the method prevents assessment of relative preponderance. Felixounaviruses often have broad within-genus host ranges, and isolates have been shown to be able to rapidly expand their host range when challenged, co-coinciding with mutations in the long tail gene [57,58]. Five of the Myoviridae are members of the newly announced genus Phapecoctavirus with substantial similarity (86-90%, BLAST) to the type species Escherichia phage phAPEC8 (JX561091) [23,59].…”