Response ofPseudomonas aeruginosato the innate immune system-derived oxidants hypochlorous acid and hypothiocyanous acid

Abstract

Pseudomonas aeruginosa is a significant nosocomial pathogen and associated with lung infections in cystic fibrosis (CF). Once established, P. aeruginosa infections persist and are rarely eradicated despite the host immune cells producing antimicrobial oxidants, including hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). There is limited knowledge as to how P. aeruginosa senses, responds to, and survives attack from HOCl and HOSCN, and the contribution of such responses to its success as a CF pathogen. We investigated the P. aeruginosa response to these oxidants by screening 707 transposon mutants, with mutations in regulatory genes, for altered growth following HOCl exposure. We identified regulators involved in antibiotic resistance, methionine biosynthesis and catabolite repression, and PA14_07340, the homologue of the Escherichia coli HOCl-sensor RclR (30% identical), that were required for HOCl survival. We have shown that RclR (PA14_07340) protects specifically against HOCl and HOSCN stress, and responds to both oxidants by upregulating expression of a putative peroxiredoxin, rclX (PA14_07355). While there was specificity in the transcriptional response to HOCl (231 genes upregulated) and HOSCN (105 genes upregulated) there was considerable overlap, with 74 genes upregulated by both oxidants. These included genes encoding the type III secretion system (T3SS), sulphur and taurine transport, and

Surviving Reactive Chlorine Stress: Responses of Gram-Negative Bacteria to Hypochlorous Acid

“…MexEF-OprN belongs to the resistance nodulation cells division (RDN) family and has been described to be involved in the resistance to fluoroquinolones, chloramphenicol, trimethoprim, and carbapenems [ 178 ]. The upregulation of genes involved in the expression of efflux pumps by HOCl has also been described in other studies [ 167 , 170 ]. For instance, Farrant and collaborators (2020) showed that MexEF-OprN mutants were more sensitive to the effects of HOCl than the wild-type [ 167 ].…”

“…The upregulation of genes involved in the expression of efflux pumps by HOCl has also been described in other studies [ 167 , 170 ]. For instance, Farrant and collaborators (2020) showed that MexEF-OprN mutants were more sensitive to the effects of HOCl than the wild-type [ 167 ]. In this context, multidrug efflux pumps could be involved not only in the export of antimicrobial agents and disinfectants but also in the transport of toxic HOCl sub-products generated by the reaction of this disinfectant with intracellular molecules.…”

“…However, the addition of 3.5 mM and 0.53 mM of HOCl and HOSCN, respectively, inhibited the formation of biofilms, suggesting thereby, that these genes are involved in the adaptation of P. aeruginosa to oxidative stress (see Section 3.2 ). RclR protects P. aeruginosa against oxidative stress by upregulating rclX , a putative peroxiredoxin [ 167 ]. RclR belongs to the AraC family and, along with HypT, is the first HOCl-sensing transcriptional regulator that responds specifically to HOCl, but do not respond to ROS and thiol-reactive compounds [ 132 ].…”

“…RclR belongs to the AraC family and, along with HypT, is the first HOCl-sensing transcriptional regulator that responds specifically to HOCl, but do not respond to ROS and thiol-reactive compounds [ 132 ]. RclR is not only involved in HOCl-stress response in biofilms, but this transcriptional regulator is also crucial for the protection of motile bacteria against exogenous HOCl [ 108 , 167 ].…”

“…Farrant et al (2020) found that the most upregulated genes in P. aeruginosa in response to HOCl exposure were non-coding RNA genes, followed by genes associated with antibiotic resistance, and protein secretion and export systems. Among the genes involved in the transport of molecules, the highly overexpressed were those involved in sulfur and taurine metabolism, indicating that bacterial cells use taurine as a sulfur source under sulfur starvation conditions, thereby the uptake of those substances should increase [ 167 ]. Additionally, exposure to HOCl also activates virulence systems used to overcome the host immune system.…”