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.
Highlights
Salmonella is an important foodborne pathogen with global recognition [1,2]
The aim of this work was to (1) characterize two Felixounaviruses with different host ranges, isolated from the same strain of Salmonella Infantis (SI) and (2) subsequently, expose them to interact in a challenge assay, to identify resistance and genetic and phenotypic changes developed upon interactions
The strain used for this assay was Salmonella Infantis CHA004-4, which was isolated from a backyard poultry production system in Chile [39]
Summary
Salmonella is an important foodborne pathogen with global recognition [1,2]. Among the 2600 serovars, Salmonella Infantis (SI) is an emerging serovar of great significance worldwide in food production, especially in poultry production [1,2]. In Europe, an increase in cases associated with this serovar has been described [1]. European Food Safety Authority (EFSA) reported SI among the five most important serovars causing human salmonellosis in Europe [1]. There are several reports of multidrug-resistant SI, including resistance to carbapenems, colistin, nalidixic acid, ciprofloxacin, tetracycline, spectinomycin, streptomycin, and sulfamethoxazole [4,5,6,7,8]. These data highlight the importance of developing innovative interventions to control SI. The use of bacteriophages or phages appears as a potential alternative to control this pathogen [9]
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