Salmonella Typhimurium uses the Cpx stress response to detect N-chlorotaurine and promote the repair of oxidized proteins

Comparative analysis reveals the trivial role of MsrP in defending oxidative stress and virulence of Salmonella Typhimurium in mice

Sulphur containing amino acids, methionine and cysteine are highly prone to oxidation. Reduction of oxidized methionine (Met-SO) residues to methionine (Met) by methionine sulfoxide reductases (Msrs) enhances the survival of bacterial pathogens under oxidative stress conditions. S. Typhimurium encodes two types (cytoplasmic and periplasmic) of Msrs. Periplasmic proteins, due to their location are highly vulnerable to host-generated oxidants. Therefore, the periplasmic Msr (MsrP) mediated repair (as compared to the cytoplasmic counterpart) might play a more imperative role in defending host-generated oxidants. Contrary to this, we show that in comparison to the ΔmsrP strain, the mutant strains in the cytoplasmic Msrs (ΔmsrA and ΔmsrAC strains) showed many folds more susceptibility to chloramine-T and neutrophils. Further ΔmsrA and ΔmsrAC strains accumulated higher levels of ROS and showed compromised fitness in mice spleen and liver. Our data suggest the pivotal role of cytoplasmic Msrs in oxidative stress survival of S. Typhimurium.

Pan msr gene deleted strain of Salmonella Typhimurium suffers oxidative stress, depicts macromolecular damage and attenuated virulence

Salmonella encounters but survives host inflammatory response. To defend host-generated oxidants, Salmonella encodes primary antioxidants and protein repair enzymes. Methionine (Met) residues are highly prone to oxidation and convert into methionine sulfoxide (Met-SO) which compromises protein functions and subsequently cellular survival. However, by reducing Met-SO to Met, methionine sulfoxide reductases (Msrs) enhance cellular survival under stress conditions. Salmonella encodes five Msrs which are specific for particular Met-SO (free/protein bound), and 'R'/'S' types. Earlier studies assessed the effect of deletions of one or two msrs on the stress physiology of S. Typhimurium. We generated a pan msr gene deletion (Δ5msr) strain in S. Typhimurium. The Δ5msr mutant strain shows an initial lag in in vitro growth. However, the Δ5msr mutant strain depicts very high sensitivity (p < 0.0001) to hypochlorous acid (HOCl), chloramine T (ChT) and superoxide-generating oxidant paraquat. Further, the Δ5msr mutant strain shows high levels of malondialdehyde (MDA), protein carbonyls, and protein aggregation. On the other side, the Δ5msr mutant strain exhibits lower levels of free amines. Further, the Δ5msr mutant strain is highly susceptible to neutrophils and shows defective fitness in the spleen and liver of mice. The results of the current study suggest that the deletions of all msrs render S. Typhimurium highly prone to oxidative stress and attenuate its virulence.