Seawater-Induced Vegetative to Dormant Phenotype Transformation of Salmonella Enteritidis

Introduction: Under the influence of sublethal stress, non-spore-forming bacteria (including Salmonella spp.) are able to form dormant cellular phenotypes that do not grow on traditional differential diagnostic media.
Objective: To study the possibility of Salmonella Enteritidis changing the phenotype from vegetative to dormant upon seawater exposure.
Materials and Methods: Salmonella Enteritidis / food / Primorsky_krai_Artyem / S-28390 / 2024 (38.0 : 1.4) strain (VGARus ID prim001916) was incubated for 40 days in parallel in sterile saline solution and sterilized seawater to establish the possibility of transforming the vegetative phenotype into a dormant one. The reversal of the dormant phenotype to the vegetative one was carried out by alimentary infestation of laboratory mice previously verified for the absence of Salmonella infection. In addition to standard bacteriological methods, we used plasmidomic analysis, real-time polymerase chain reaction for DNA detection of Salmonella, and genome-wide next-generation sequencing (NGS).
Results: We found that long-term incubation in seawater triggered the mechanism of transformation of the vegetative phenotype of S. Enteritidis into a dormant one. Similar incubation of S. Enteritidis but in saline solution did not cause such a transformation, bacterial cells naturally died in the absence of nutrients, but the remaining viable cells did not become dormant. Reversion to the vegetative phenotype occurred after passage of the dormant form in orally inoculated laboratory mice. The identity of the genomes of the strains in the dormant state used for alimentary infestation of the mice and in the vegetative state obtained after passage was confirmed by a 99.8 % NGS contig match.
Conclusions: As an abiotic factor, sterilized seawater can trigger the mechanism of S. Enteritidis vegetative to dormant phenotype transformation. This requires detailing of hygienic requirements for recreational areas of seacoasts in terms of developing methods for detection of pathogenic bacteria with a dormant phenotype.

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