Repeated in-vitro and in-vivo exposure leads to genetic alteration, adaptations, and hypervirulence in Salmonella

Adaptation is an important phenomenon for the survival of any organism in various in-vitro and in-vivo conditions leading to their better survival. We studied Salmonella, for the evolutionary adaptation under different conditions. When Salmonella was passaged for 12 rounds in Luria Bertani (P12-STM) media, F media (F12-STM) and Caenorhabditis elegans (Ce12-STM), we found certain phenotypic variations with respect to unpassaged strain. The passaged strains showed a significant increase in motility, body size and number of flagella they possessed, increased tolerance to ROS and RNS under in-vitro condition. They were more invasive in the human intestinal epithelial cells (Int-407) and showed a higher proliferation rate in the phagocytic cells (U-937 and RAW-264.7) suggesting their efficient intracellular proliferation. The evolved strains were hyper-infectious and reduced host viability significantly in C. elegans. The upregulation of various virulent and regulatory genes observed could be associated with the evolved adaptive virulent phenotype by Salmonella in a given condition. Whole genome sequencing also indicates the genetic alteration including insertion and deletions, single nucleotide polymorphisms which are common in all the strains as well as exposure specific, giving varied phenotype among the passaged strains. This study indicates that Salmonella is showing adaptation, genetic alteration and have become hypervirulent hence is capable of causing disease severity.