Eradication Of Persister Cells And Identification Of Molecular Targets Of The Type-Ⅰ Toxin-antitoxin System In Methicillin-Resistant Staphylococcus Aureus

Methicillin-resistant Staphylococcus aureus is the major culprit of the emergence of community-acquired MRSA and hospital-acquired MRSA,making the eradication of antibiotic-resistant S.aureus more difficult and severe.Antibiotic resistance is not new to staphylococcal pathogenesis but day by day the status of resistance is becoming more challenging.These resistant strains of S.aureus can produce diverse types of cells that don’t acquire resistance but maintain a state of dormancy called persistence.Persistence is the ability of cells to tolerate unfavorable conditions and multiple stresses such as antibiotics and heat shock.There are less known and more unknown factors that either alleviate or aggravate persistence phenomenon.A typical toxin-antitoxin(TA)system is a set of two-component system that codes for toxin and its antidote.TA systems are involved in premeditated or spontaneous cellular action,leading to inhibition of various cellular processes namely transcription,translation,replication and many unknown.S.aureus is the most versatile species of the genus Staphylococcus that is equipped with a repertoire of TA systems but a restricted palette of TA systems have been characterized.To date,only two type Ⅰ and three types Ⅱ TA systems have been studied in S.aureus.The function of these putative TA systems in S.aureus showed high divergence but showed no functional roles in increase or decrease in persister cells formation in S.aureus.ATP depletion increased persister cells formation in S.aureus,whereas how these cells will be eradicated is still elusive in methicillin-resistant S.aureus.Here we have investigated TA systems in S.aureus and identified 15 putative TA systems including the previously reported three TA systems.We classified the TA systems into two major groups i.e.pathogenicity islands TA system and non-pathogenicity islands TA systems.We witnessed that the pathogenicity islands TA systems contribute to cellular toxicity in MRSA while non-pathogenicity islands TA systems have no such capability.Further,we characterized a novel three-component type-Ⅰ TA system whose toxin gene has pleiotropic effects that can decrease persister cells formation in S.aureus.The toxin ectopic induction creates an intracellular state of menace that leads to the inhibition of type seven secretion system core component EssC,multidrug resistant efflux pump NorA and sodium-proton antiporter system.In addition,the toxin targets 50S ribosomal proteins L17 and L10 and activates ClpP protease.The ClpP protease is a protein degradative enzymes and targets toxin protein.The deletion of this toxin gene from bacterial genome increased the survival of persister cells,which showed the pernicious nature of toxin.The action of toxin gene is counterbalanced by its antitoxin,resulting in suppression of cellular toxicity.In this TA system,for the toxin,there is a transcriptional regulator that can enhance the toxin expression under stress conditions.Hence,toxin-antitoxin-regulator is a new three-component type Ⅰ TA system that decreased persister cells formation in S.aureus.