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Evolutionary loss of an antibiotic efflux pump increases Pseudomonas aeruginosa quorum sensing mediated virulence in vivo

ABSTRACT: Antibiotic resistance is one of the most pressing threats to human health, yet recent work highlights how loss of resistance may also drive pathogenesis in some bacteria. In two recent studies, we found that in vitro beta-lactam antibiotic and nutrient stresses faced during infection selected for the genetic inactivation of the Pseudomonas aeruginosa (Pa) antibiotic efflux pump mexEFoprN. Unexpectedly, efflux pump mutations increased Pa virulence during infection; however, neither the prevalence of efflux pump inactivating mutations in real human infections, nor the mechanisms driving increased virulence of efflux pump mutants were known. We hypothesized that human infection would select for efflux pump mutations that drive increased virulence in Pa clinical isolates. Using genome sequencing of hundreds of Pa clinical isolates, we show that mexEFoprN efflux pump inactivating mutations are enriched in Pa cystic fibrosis isolates relative to Pa intensive care unit clinical isolates. Combining RNA-seq, metabolomics, genetic approaches, and infection models we show that efflux pump mutants increase expression of two key Pa virulence factors, elastase and rhamnolipids, which increased Pa virulence and lung damage during both acute and chronic infections. We show that increased virulence factor production was driven by increased Pseudomonas quinolone signal levels, and this mechanism of increased virulence held true in both a representative ICU clinical isolate and the notorious CF Pa Liverpool epidemic strain. Together, our findings suggest that mutations inactivating antibiotic resistance mechanisms could increase patient mortality and morbidity.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Pseudomonas Aeruginosa Pao1 (ncbitaxon:208964)

SUBMITTER: Peter Jorth

PROVIDER: MSV000096391 | MassIVE | Tue Nov 12 09:14:00 GMT 2024

REPOSITORIES: MassIVE

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Project description:Pseudomonas aeruginosa (Pa) is a ubiquitous bacterium that uses quorum sensing (QS), a cell-cell communication system that enables it to sense cell density and to alter gene expression. Pa has three complete QS circuits controlled by the transcriptional regulators LasR, RhlR, and PqsR (MvfR), that together control hundreds of genes, including virulence factors. In the well-described strain PAO1, QS is organized hierarchically, with PqsR and RhlR activity dependent on LasR. In PAO1, this hierarchy depends on the non-QS transcription factor MexT; by an unknown mechanism, deletion of mexT allows for RhlR activity in the absence of LasR. We aimed to identify how regulators such as MexT modulate the QS architecture in Pa. We compared the transcriptome of PAO1 to that of PAO1ΔmexT and identified 152 differentially expressed genes. MexT does not appear to regulate rhlR or pqsR directly; however, we identified two MexT-regulated operons that may affect the hierarchy in PAO1. These operons encode the drug efflux pump genes mexEF-oprN and the Pseudomonas quinolone signal (PQS) synthesis genes pqsABCDE. We performed genetic experiments to test whether the products of these genes affected the QS hierarchy. As with the mexT knockout mutant, we found that a PAO1 mexEF knockout mutant exhibited RhlR activity earlier, and to a higher magnitude, than wild-type PAO1. MexEF-OprN is known to export the PQS precursor HHQ, and we found that exogenous addition of PQS to PAO1 partially affects RhlR activity, resulting in earlier timing and higher magnitude compared to wild-type PAO1. We further elucidated that this is likely due to positive regulation by PqsE. These data link both the drug efflux pump MexEF-OprN and PQS QS to the regulation of the QS hierarchy in PAO1. We wondered if the same applied to QS architectures in Pa clinical isolates. We discovered that there are alternate QS architectures in clinical isolates, where RhlR activity is not fully dependent on LasR. In these isolates, surprisingly, MexT does not influence the relationship between LasR and RhlR, and this is indicative of a different QS architecture in the clinical isolates. Overall, we further elucidated the regulation of QS architecture in PAO1 and identified unique QS architectures in clinical isolates. Importantly, our work reveals a new suite of factors that regulate QS in Pa, with implications for a variety of Pa behaviors both in the laboratory and clinical settings.

Project description:Purpose: Recently we have characterize 43 clinical isolates of Pseudomonas aeruginosa overproducing the efflux pump MexEF-OprN. About 45% of these strains did not display mutations in any of the regulators known to control mexEF-oprN expression. Here we identified a novel regulator of the efflux operon mexEF-oprN that we named CmrA by characterizing in vitro selected mutants from the strain PA14. Methods: MexEF-OprN overproducing spontaneous mutants were selected in vitro using the reference strain PA14 in presence of chloramphenicol. Selected mutants (PJ mutants) were characterized using different criteria such as antibiotic susceptibility and production of virulence traits. Gene expression was evaluated by RT-qPCR. Whole genome sequencing of selected mutants (PJ mutants) was performed using IonTorrent technology. Knock-out mutants were constructed by overlapping PCR and homologous recombination. Finally, a transcriptomic analysis by RNAseq was performed to identify the genes depending on CmrA. Results: Characterization of the 4 selected PJ mutants showed that these strains have resistance and virulence profiles slightly differentent from those typically observed in MexEF-OprN overproducing strains (mexS- NfxC strains). The cmrA+ strains (here called NfxC2) showed moderate resistance to MexEF-OprN antibiotic substrates (ciprofloxacin, chloramphenicol and trimethoprim from 8- to 32-fold compared to PA14) and showed a less compromised capacity to produce some virulence traits (rhamnolipids, elastase, biofilm and pyocyanin) as well as the swarming motility. Whole genome sequencing of PJ mutants led to the identification of SNPs in the gene PA14_38040 (PA14_RS15465 after 2015 genome annotation uptdate). The gene PA14_RS15465 codes for an unknown transcriptional activator and was named cmrA for chlormaphenicol resistance activator. Aminoacid substitutions in CmrA found in PJ mutants were shown to constantly activate this regulator. Further characterization by gene inactivation showed that cmrA is responsible for the activation of the expression of the mexEF-oprN operon in PJ mutants. The locus cmrA was characterized and the complete sequence, including regulatory sequeces, was submitted to GenBank (accession number KX274690). Further analysis showed that the CmrA-activating pathway was dependent on mexS and mexT, both genes are known to affect mexEF-oprN expression. Finally, the transcriptomic analysis of the PJ01 mutant (compared to PA14 and to PJ01∆mexT) revealed that CmrA significally activate the expression of 11 genes most of them coding for enzymes involved in redox regulation. Conclusions: The discovery of cmrA opens the posibility to give an explanation to those clinical strains overproducing the efflux pump MexEF-OprN for unknown reasons. Our data shows that this regulator can activate the efflux pump in a way that the strain is capable to tolerate the antibiotics substrates of the pump and to mantain its capacity to produce some virulence traits. CmrA seems to have a role in the activation of regulatory pathways involved in redox homeostasis as shown by the transcriptomic analysis. The fact that the MexEF-OprN pump is activated at the same time that a redox system let us think that this pump could be related to intracellular detoxification of molecules altering the intracellular homeostasis as it has been previously proposed. We are currently analyzing the transcriptome of CmrA to describe the whole activation pathway of this regulator.

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Evolutionary loss of an antibiotic efflux pump increases Pseudomonas aeruginosa quorum sensing mediated virulence in vivo

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