Ferric Uptake Regulator Fur Is Conditionally Essential in Pseudomonas aeruginosa

ABSTRACT In Pseudomonas aeruginosa, the ferric uptake regulator (Fur) protein controls both metabolism and virulence in response to iron availability. Differently from other bacteria, attempts to obtain fur deletion mutants of P. aeruginosa failed, leading to the assumption that Fur is an essential protein in this bacterium. By investigating a P. aeruginosa conditional fur mutant, we demonstrate that Fur is not essential for P. aeruginosa growth in liquid media, biofilm formation, and pathogenicity in an insect model of infection. Conversely, Fur is essential for growth on solid media since Fur-depleted cells are severely impaired in colony formation. Transposon-mediated random mutagenesis experiments identified pyochelin siderophore biosynthesis as a major cause of the colony growth defect of the conditional fur mutant, and deletion mutagenesis confirmed this evidence. Impaired colony growth of pyochelin-proficient Fur-depleted cells does not depend on oxidative stress, since Fur-depleted cells do not accumulate higher levels of reactive oxygen species (ROS) and are not rescued by antioxidant agents or overexpression of ROS-detoxifying enzymes. Ectopic expression of pch genes revealed that pyochelin production has no inhibitory effects on a fur deletion mutant of Pseudomonas syringae pv. tabaci, suggesting that the toxicity of the pch locus in Fur-depleted cells involves a P. aeruginosa-specific pathway(s). IMPORTANCE Members of the ferric uptake regulator (Fur) protein family are bacterial transcriptional repressors that control iron uptake and storage in response to iron availability, thereby playing a crucial role in the maintenance of iron homeostasis. While fur null mutants of many bacteria have been obtained, Fur appears to be essential in Pseudomonas aeruginosa for still unknown reasons. We obtained Fur-depleted P. aeruginosa cells by conditional mutagenesis and showed that Fur is dispensable for planktonic growth, while it is required for colony formation. This is because Fur protects P. aeruginosa colonies from toxicity exerted by the pyochelin siderophore. This work provides a functional basis to the essentiality of Fur in P. aeruginosa and highlights unique properties of the Fur regulon in this species.

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Regulation of Iron Uptake by Fine-Tuning the Iron Responsiveness of the Iron Sensor Fur

Applied and Environmental Microbiology ◽

10.1128/aem.03026-18 ◽

2019 ◽

Vol 85 (9) ◽

Cited By ~ 2

Author(s):

Jeongjoon Choi ◽

Sangryeol Ryu

Keyword(s):

Iron Uptake ◽

Metal Ion ◽

Iron Homeostasis ◽

Control Mechanism ◽

Fine Tuning ◽

Ferric Uptake Regulator ◽

Biological Processes ◽

Iron Availability ◽

Fur Protein ◽

Iron Concentrations

ABSTRACTIron is one of most abundant environmental metal ions but is highly limited in organisms. It is an important metal ion as it facilitates various biological processes, including catalysis of metabolic enzymes and DNA biogenesis. In bacteria, the ferric uptake regulator (Fur) protein controls iron uptake by regulating genes coding for iron transporters in response to iron concentration. This iron response is ascribed to Fur’s intrinsic affinity for iron because its binding to iron dictates its regulatory function. However, we now report that the pathogenSalmonellaachieves a proper response of Fur to changes in environmental iron concentrations via EIIANtr(a nitrogen metabolic phosphotransferase system component). We establish that EIIANtrincreases expression of iron transporter-coding genes under low-iron conditions (i.e., nanomolar ranges) in a Fur-dependent manner, which promotesSalmonellagrowth under such conditions. EIIANtrdirectly hampers Fur binding to DNA, thereby inducing expression of those genes. This regulation allowsSalmonellato express Fur-regulated genes under low-iron conditions. Our findings reveal a potentially widespread control mechanism of bacterial iron uptake systems operating in response to iron availability.IMPORTANCEIron is a fundamental metal ion for living organisms as it facilitates various biological processes. The ferric uptake regulator (Fur) protein controls iron homeostasis in various bacterial species. It is believed that Fur’s iron-dependent regulatory action is sufficient for it to function as an iron sensor. However, we now establish that the bacterial pathogenSalmonellaenables Fur to properly reflect changes in surrounding iron availability by fine-tuning its responsiveness to iron. This process requires a protein that hampers Fur DNA binding at low iron concentrations. In this way,Salmonellabroadens the range of iron concentrations that Fur responds to. Our findings reveal a potentially widespread control mechanism of bacterial iron homeostasis.

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Pyoverdine and Proteases Affect the Response of Pseudomonas aeruginosa to Gallium in Human Serum

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01097-15 ◽

2015 ◽

Vol 59 (9) ◽

pp. 5641-5646 ◽

Cited By ~ 24

Author(s):

Carlo Bonchi ◽

Emanuela Frangipani ◽

Francesco Imperi ◽

Paolo Visca

Keyword(s):

Cystic Fibrosis ◽

Pseudomonas Aeruginosa ◽

Human Serum ◽

Bloodstream Infections ◽

Proteinase K ◽

Gallium Nitrate ◽

Iron Availability ◽

Content Type ◽

Iron Restriction ◽

Casamino Acids

ABSTRACTGallium is an iron mimetic which has recently been repurposed as an antibacterial agent due to its capability to disrupt bacterial iron metabolism. In this study, the antibacterial activity of gallium nitrate [Ga(NO3)3] was investigated in complement-free human serum (HS) on 55Pseudomonas aeruginosaclinical isolates from cystic fibrosis and non-cystic fibrosis patients. The susceptibility ofP. aeruginosato Ga(NO3)3in HS was dependent on the bacterial ability to acquire iron from serum binding proteins (i.e., transferrin). The extent of serum protein degradation correlated well withP. aeruginosagrowth in HS, while pyoverdine production did not. However, pyoverdine-deficientP. aeruginosastrains were unable to grow in HS and overcome iron restriction, albeit capable of releasing proteases. Predigestion of HS with proteinase K promoted the growth of all strains, irrespective of their ability to produce proteases and/or pyoverdine. The MICs of Ga(NO3)3were higher in HS than in an iron-poor Casamino Acids medium, where proteolysis does not affect iron availability. Coherently, strains displaying high proteolytic activity were less susceptible to Ga(NO3)3in HS. Our data support a model in which both pyoverdine and proteases affect the response ofP. aeruginosato Ga(NO3)3in HS. The relatively high Ga(NO3)3concentration required to inhibit the growth of highly proteolyticP. aeruginosaisolates in HS poses a limitation to the potential of Ga(NO3)3in the treatment ofP. aeruginosabloodstream infections.

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Silica-Induced Protein (Sip) in Thermophilic Bacterium Thermus thermophilus Responds to Low Iron Availability

Applied and Environmental Microbiology ◽

10.1128/aem.04027-15 ◽

2016 ◽

Vol 82 (11) ◽

pp. 3198-3207 ◽

Cited By ~ 4

Author(s):

Yasuhiro Fujino ◽

Yuko Nagayoshi ◽

Makoto Iwase ◽

Takushi Yokoyama ◽

Toshihisa Ohshima ◽

...

Keyword(s):

Iron Deficiency ◽

Abc Transporter ◽

Colloidal Silica ◽

Thermus Thermophilus ◽

Thermophilic Bacterium ◽

Geothermal Water ◽

Ferric Uptake Regulator ◽

Iron Availability ◽

Content Type ◽

Silicic Acids

ABSTRACTThermus thermophilusHB8 expresses silica-induced protein (Sip) when cultured in medium containing supersaturated silicic acids. Using genomic information, Sip was identified as a Fe3+-binding ABC transporter. Detection of a 1-kb hybridized band in Northern analysis revealed thatsiptranscription is monocistronic and thatsiphas its own terminator and promoter. The sequence of thesippromoter showed homology with that of the σA-dependent promoter, which is known as a housekeeping promoter in HB8. Considering thatsipis transcribed when supersaturated silicic acids are added, the existence of a repressor is presumed. DNA microarray analysis suggested that supersaturated silicic acids and iron deficiency affectThermuscells similarly, and enhancedsiptranscription was detected under both conditions. This suggested thatsiptranscription was initiated by iron deficiency and that the ferric uptake regulator (Fur) controlled the transcription. Three Fur gene homologues (TTHA0255, TTHA0344, and TTHA1292) have been annotated in the HB8 genome, and electrophoretic mobility shift assays revealed that the TTHA0344 product interacts with thesippromoter region. In medium containing supersaturated silicic acids, free Fe3+levels were decreased due to Fe3+immobilization on colloidal silica. This suggests that, because Fe3+ions are captured by colloidal silica in geothermal water,Thermuscells are continuously exposed to the risk of iron deficiency. Considering that Sip is involved in iron acquisition, Sip production may be a strategy to survive under conditions of low iron availability in geothermal water.IMPORTANCEThe thermophilic bacteriumThermus thermophilusHB8 produces silica-induced protein (Sip) in the presence of supersaturated silicic acids. Sip has homology with iron-binding ABC transporter; however, the mechanism by which Sip expression is induced by silicic acids remains unexplained. We demonstrate that Sip captures iron and its transcription is regulated by the repressor ferric uptake regulator (Fur). This implies that Sip is expressed with iron deficiency. In addition, it is suggested that negatively charged colloidal silica in supersaturated solution absorbs Fe3+ions and decreases iron availability. Considering that geothermal water contains ample silicic acids, it is suggested that thermophilic bacteria are always facing iron starvation. Sip production may be a strategy for surviving under conditions of low iron availability in geothermal water.

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Roles of RcsA, an AhpD Family Protein, in Reactive Chlorine Stress Resistance and Virulence in Pseudomonas aeruginosa

Applied and Environmental Microbiology ◽

10.1128/aem.01480-20 ◽

2020 ◽

Vol 86 (20) ◽

Author(s):

Benya Nontaleerak ◽

Jintana Duang-nkern ◽

Lampet Wongsaroj ◽

Wachareeporn Trinachartvanit ◽

Adisak Romsang ◽

...

Keyword(s):

Escherichia Coli ◽

Pseudomonas Aeruginosa ◽

Hypochlorous Acid ◽

Ectopic Expression ◽

Fruit Fly ◽

Opportunistic Pathogen ◽

Model Systems ◽

Harsh Environments ◽

Core Motif ◽

Content Type

ABSTRACT Reactive chlorine species (RCS), particularly hypochlorous acid (HOCl), are powerful antimicrobial oxidants generated by biological pathways and chemical syntheses. Pseudomonas aeruginosa is an important opportunistic pathogen that has adapted mechanisms for protection and survival in harsh environments, including RCS exposure. Based on previous transcriptomic studies of HOCl exposure in P. aeruginosa, we found that the expression of PA0565, or rcsA, which encodes an alkyl hydroperoxidase D-like protein, exhibited the highest induction among the RCS-induced genes. In this study, rcsA expression was dominant under HOCl stress and greatly increased under HOCl-related stress conditions. Functional analysis of RcsA showed that the distinguishing core amino acid residues Cys60, Cys63, and His67 were required for the degradation of sodium hypochlorite (NaOCl), suggesting an extended motif in the AhpD family. After allelic exchange mutagenesis in the P. aeruginosa rcsA, the P. aeruginosa rcsA deletion mutant showed significantly decreased HOCl resistance. Ectopic expression of P. aeruginosa rcsA led to significantly increased NaOCl resistance in Escherichia coli. Moreover, the pathogenicity of the rcsA mutant decreased dramatically in both Caenorhabditis elegans and Drosophila melanogaster host model systems compared to the wild type (WT). Finally, the Cys60, Cys63, and His67 variants of RcsA were unsuccessful at complementing phenotypes of the rcsA mutant. Overall, our data indicate the importance of P. aeruginosa RcsA in defense against HOCl stress under disinfections and during infections of hosts, which involves the catalytic Cys60, Cys63, and His67 residues. IMPORTANCE Pseudomonas aeruginosa is a common pathogen that is a major cause of serious infections in many hosts. Hypochlorous acid (HOCl) is a potent antimicrobial agent found in household bleach and is a widely used disinfectant. P. aeruginosa has evolved adaptive mechanisms for protection and survival during HOCl exposure. We identified P. aeruginosa rcsA as a HOCl-responsive gene encoding an antioxidant protein that may be involved in HOCl degradation. RcsA has a distinguishing core motif containing functional Cys60, Cys63, and His67 residues. P. aeruginosa rcsA plays an important role in bleach tolerance, with expression of P. aeruginosa rcsA in Escherichia coli also conferring HOCl resistance. Interestingly, RcsA is required for full virulence in worm and fruit fly infection models, indicating a correlation between mechanisms of bleach toxicity and host immunity during infection. This provides new insights into the mechanisms used by P. aeruginosa to persist in harsh environments such as hospitals.

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Distinct Contributions of CD18 Integrins for Binding and Phagocytic Internalization of Pseudomonas aeruginosa

Infection and Immunity ◽

10.1128/iai.00011-20 ◽

2020 ◽

Vol 88 (5) ◽

Cited By ~ 1

Author(s):

Sally Demirdjian ◽

Daniel Hopkins ◽

Nadia Cumbal ◽

Craig T. Lefort ◽

Brent Berwin

Keyword(s):

Pseudomonas Aeruginosa ◽

Leukocyte Adhesion ◽

Ectopic Expression ◽

Bacterial Pathogen ◽

Host Cells ◽

Bacterial Motility ◽

Cell Surface Receptor ◽

Chronic Infections ◽

Content Type ◽

Deficiency Type

ABSTRACT Phagocytosis is the key mechanism for host control of Pseudomonas aeruginosa, a motile Gram-negative, opportunistic bacterial pathogen which frequently undergoes adaptation and selection for traits that are advantageous for survival. One such clinically relevant adaptation is the loss of bacterial motility, observed within chronic infections, that is associated with increased antibiotic tolerance and phagocytic resistance. Previous studies using phagocytes from a leukocyte adhesion deficiency type 1 (LAD-I) patient identified CD18 as a putative cell surface receptor for uptake of live P. aeruginosa. However, how bacterial motility alters direct engagement with CD18-containing integrins remains unknown. Here we demonstrate, with the use of motile and isogenic nonmotile deletion mutants of two independent strains of P. aeruginosa and with CRISPR-generated CD18-deficient cell lines in human monocytes and murine neutrophils, that CD18 expression facilitates the uptake of both motile and nonmotile P. aeruginosa. However, unexpectedly, mechanistic studies revealed that CD18 expression was dispensable for the initial attachment of the bacteria to the host cells, which was validated with ectopic expression of complement receptor 3 (CR3) by CHO cells. Our data support that surface N-linked glycan chains (N-glycans) likely facilitate the initial interaction of bacteria with monocytes and cooperate with CD18 integrins in trans to promote internalization of bacteria. Moreover, talin-1 and kindlin-3 proteins promote uptake, but not binding, of P. aeruginosa by murine neutrophils, which supports a role for CD18 integrin signaling in this process. These findings provide novel insights into the cellular determinants for phagocytic recognition and uptake of P. aeruginosa.

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Pseudomonas aeruginosa PA14 Enhances the Efficacy of Norfloxacin against Staphylococcus aureus Newman Biofilms

Journal of Bacteriology ◽

10.1128/jb.00159-20 ◽

2020 ◽

Vol 202 (18) ◽

Cited By ~ 1

Author(s):

Giulia Orazi ◽

Fabrice Jean-Pierre ◽

George A. O’Toole

Keyword(s):

Cystic Fibrosis ◽

Staphylococcus Aureus ◽

Pseudomonas Aeruginosa ◽

Antimicrobial Agents ◽

Respiratory Infections ◽

Multiple Infection ◽

Bacterial Biofilms ◽

Interspecies Interactions ◽

Chronic Infections ◽

Content Type

ABSTRACT The thick mucus within the airways of individuals with cystic fibrosis (CF) promotes frequent respiratory infections that are often polymicrobial. Pseudomonas aeruginosa and Staphylococcus aureus are two of the most prevalent pathogens that cause CF pulmonary infections, and both are among the most common etiologic agents of chronic wound infections. Furthermore, the ability of P. aeruginosa and S. aureus to form biofilms promotes the establishment of chronic infections that are often difficult to eradicate using antimicrobial agents. In this study, we found that multiple LasR-regulated exoproducts of P. aeruginosa, including 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), siderophores, phenazines, and rhamnolipids, likely contribute to the ability of P. aeruginosa PA14 to shift S. aureus Newman norfloxacin susceptibility profiles. Here, we observe that exposure to P. aeruginosa exoproducts leads to an increase in intracellular norfloxacin accumulation by S. aureus. We previously showed that P. aeruginosa supernatant dissipates the S. aureus membrane potential, and furthermore, depletion of the S. aureus proton motive force recapitulates the effect of the P. aeruginosa PA14 supernatant on shifting norfloxacin sensitivity profiles of biofilm-grown S. aureus Newman. From these results, we hypothesize that exposure to P. aeruginosa PA14 exoproducts leads to increased uptake of the drug and/or an impaired ability of S. aureus Newman to efflux norfloxacin. Surprisingly, the effect observed here of P. aeruginosa PA14 exoproducts on S. aureus Newman susceptibility to norfloxacin seemed to be specific to these strains and this antibiotic. Our results illustrate that microbially derived products can alter the ability of antimicrobial agents to kill bacterial biofilms. IMPORTANCE Pseudomonas aeruginosa and Staphylococcus aureus are frequently coisolated from multiple infection sites, including the lungs of individuals with cystic fibrosis (CF) and nonhealing diabetic foot ulcers. Coinfection with P. aeruginosa and S. aureus has been shown to produce worse outcomes compared to infection with either organism alone. Furthermore, the ability of these pathogens to form biofilms enables them to cause persistent infection and withstand antimicrobial therapy. In this study, we found that P. aeruginosa-secreted products dramatically increase the ability of the antibiotic norfloxacin to kill S. aureus biofilms. Understanding how interspecies interactions alter the antibiotic susceptibility of bacterial biofilms may inform treatment decisions and inspire the development of new therapeutic strategies.

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In VitroActivity of Glucosinolates and Their Degradation Products against Brassica-Pathogenic Bacteria and Fungi

Applied and Environmental Microbiology ◽

10.1128/aem.03142-14 ◽

2014 ◽

Vol 81 (1) ◽

pp. 432-440 ◽

Cited By ~ 39

Author(s):

T. Sotelo ◽

M. Lema ◽

P. Soengas ◽

M. E. Cartea ◽

P. Velasco

Keyword(s):

Pseudomonas Syringae ◽

Xanthomonas Campestris ◽

Pathogenic Bacteria ◽

Degradation Products ◽

Allyl Isothiocyanate ◽

Leaf Extracts ◽

Soil Pathogens ◽

Content Type ◽

Positive Effects

ABSTRACTGlucosinolates (GSLs) are secondary metabolites found inBrassicavegetables that confer on them resistance against pests and diseases. Both GSLs and glucosinolate hydrolysis products (GHPs) have shown positive effects in reducing soil pathogens. Information about theirin vitrobiocide effects is scarce, but previous studies have shown sinigrin GSLs and their associated allyl isothiocyanate (AITC) to be soil biocides. The objective of this work was to evaluate the biocide effects of 17 GSLs and GHPs and of leaf methanolic extracts of different GSL-enrichedBrassicacrops on suppressingin vitrogrowth of two bacterial (Xanthomonas campestrispv. campestris andPseudomonas syringaepv. maculicola) and two fungal (AlternariabrassicaeandSclerotiniascletoriorum)Brassicapathogens. GSLs, GHPs, and methanolic leaf extracts inhibited the development of the pathogens tested compared to the control, and the effect was dose dependent. Furthermore, the biocide effects of the different compounds studied were dependent on the species and race of the pathogen. These results indicate that GSLs and their GHPs, as well as extracts of differentBrassicaspecies, have potential to inhibit pathogen growth and offer new opportunities to study the use ofBrassicacrops in biofumigation for the control of multiple diseases.

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Ocimum campechianum Mill. from Amazonian Ecuador: Chemical Composition and Biological Activities of Extracts and Their Main Constituents (Eugenol and Rosmarinic Acid)

Molecules ◽

10.3390/molecules26010084 ◽

2020 ◽

Vol 26 (1) ◽

pp. 84

Author(s):

Massimo Tacchini ◽

Monica Paulina Echeverria Guevara ◽

Alessandro Grandini ◽

Immacolata Maresca ◽

Matteo Radice ◽

...

Keyword(s):

Mass Spectrometry ◽

Pseudomonas Syringae ◽

Rosmarinic Acid ◽

Plant Protection ◽

Biological Activities ◽

Radical Scavenger ◽

Radical Scavenger Activity ◽

Antioxidant Agents ◽

Scavenger Activity

The essential oil (EO), the methanolic (MeOH), and the 70% ethanolic (70% EtOH) extracts obtained from the aerial parts of Ocimum campechianum Mill. (Ecuador) were chemically characterized through gas-chromatography coupled to mass spectrometry detector (GC-MS), high-performance liquid chromatography coupled to diode array-mass spectrometry detectors (HPLC-DAD-MS) and studied for their in vitro biological activity. The radical scavenger activity, performed by spectrophotometric 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays, highlighted significant IC50 values for the EO, extracts and their main constituents (eugenol and rosmarinic acid). EO (and eugenol) showed noteworthy activity against Pseudomonas syringae pv. syringae and a moderate effect against clinical Candida strains, with possible synergism in association to fluconazole against the latter microorganisms. The extracts and pure molecules exhibited weak cytotoxic activity against the HaCat cell line and no mutagenicity against Salmonella typhimurium TA98 and TA100 strains, giving indication of safety. Instead, EO showed a weak activity against adenocarcinomic human alveolar basal epithelial cells (A549). The above-mentioned evidence leads us to suggest a potential use of the crude drug, extracts, and EO in cosmetic formulation and food supplements as antioxidant agents. In addition, EO may also have a possible application in plant protection and anti-Candida formulations.

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Resistance and Heteroresistance to Colistin in Pseudomonas aeruginosa Isolates from Wenzhou, China

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00556-19 ◽

2019 ◽

Vol 63 (10) ◽

Cited By ~ 8

Author(s):

Jie Lin ◽

Chunquan Xu ◽

Renchi Fang ◽

Jianming Cao ◽

Xiucai Zhang ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Lipid A ◽

Population Analysis ◽

Colistin Resistance ◽

Content Type ◽

Maldi Tof Ms ◽

Expression Levels ◽

Maldi Tof ◽

Broth Microdilution Method ◽

Tof Ms

ABSTRACT The goal was to investigate the mechanisms of colistin resistance and heteroresistance in Pseudomonas aeruginosa clinical isolates. Colistin resistance was determined by the broth microdilution method. Colistin heteroresistance was evaluated by population analysis profiling. Time-kill assays were also conducted. PCR sequencing was performed to detect the resistance genes among (hetero)resistant isolates, and quantitative real-time PCR assays were performed to determine their expression levels. Pulsed-field gel electrophoresis and multilocus sequence typing were performed. Lipid A characteristics were determined via matrix-assisted laser desorption–ionization time of flight mass spectrometry (MALDI-TOF MS). Two resistant isolates and 9 heteroresistant isolates were selected in this study. Substitutions in PmrB were detected in 2 resistant isolates. Among heteroresistant isolates, 8 of 9 heteroresistant isolates had nonsynonymous PmrB substitutions, and 2 isolates, including 1 with a PmrB substitution, had PhoQ alterations. Correspondingly, the expression levels of pmrA or phoP were upregulated in PmrB- or PhoQ-substituted isolates. One isolate also found alterations in ParRS and CprRS. The transcript levels of the pmrH gene were observed to increase across all investigated isolates. MALDI-TOF MS showed additional 4-amino-4-deoxy-l-arabinose (l-Ara4N) moieties in lipid A profiles in (hetero)resistant isolates. In conclusion, both colistin resistance and heteroresistance in P. aeruginosa in this study mainly involved alterations of the PmrAB regulatory system. There were strong associations between mutations in specific genetic loci for lipid A synthesis and regulation of modifications to lipid A. The transition of colistin heteroresistance to resistance should be addressed in future clinical surveillance.

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Exogenous Alginate Protects Staphylococcus aureus from Killing by Pseudomonas aeruginosa

Journal of Bacteriology ◽

10.1128/jb.00559-19 ◽

2019 ◽

Vol 202 (8) ◽

Cited By ~ 2

Author(s):

Courtney E. Price ◽

Dustin G. Brown ◽

Dominique H. Limoli ◽

Vanessa V. Phelan ◽

George A. O’Toole

Keyword(s):

Staphylococcus Aureus ◽

Pseudomonas Aeruginosa ◽

Physical Space ◽

Late Time ◽

Protective Effects ◽

Content Type ◽

Alginate Production ◽

The Impact

ABSTRACT Cystic fibrosis (CF) patients chronically infected with both Pseudomonas aeruginosa and Staphylococcus aureus have worse health outcomes than patients who are monoinfected with either P. aeruginosa or S. aureus. We showed previously that mucoid strains of P. aeruginosa can coexist with S. aureus in vitro due to the transcriptional downregulation of several toxic exoproducts typically produced by P. aeruginosa, including siderophores, rhamnolipids, and HQNO (2-heptyl-4-hydroxyquinoline N-oxide). Here, we demonstrate that exogenous alginate protects S. aureus from P. aeruginosa in both planktonic and biofilm coculture models under a variety of nutritional conditions. S. aureus protection in the presence of exogenous alginate is due to the transcriptional downregulation of pvdA, a gene required for the production of the iron-scavenging siderophore pyoverdine as well as the downregulation of the PQS (Pseudomonas quinolone signal) (2-heptyl-3,4-dihydroxyquinoline) quorum sensing system. The impact of exogenous alginate is independent of endogenous alginate production. We further demonstrate that coculture of mucoid P. aeruginosa with nonmucoid P. aeruginosa strains can mitigate the killing of S. aureus by the nonmucoid strain of P. aeruginosa, indicating that the mechanism that we describe here may function in vivo in the context of mixed infections. Finally, we investigated a panel of mucoid clinical isolates that retain the ability to kill S. aureus at late time points and show that each strain has a unique expression profile, indicating that mucoid isolates can overcome the S. aureus-protective effects of mucoidy in a strain-specific manner. IMPORTANCE CF patients are chronically infected by polymicrobial communities. The two dominant bacterial pathogens that infect the lungs of CF patients are P. aeruginosa and S. aureus, with ∼30% of patients coinfected by both species. Such coinfected individuals have worse outcomes than monoinfected patients, and both species persist within the same physical space. A variety of host and environmental factors have been demonstrated to promote P. aeruginosa-S. aureus coexistence, despite evidence that P. aeruginosa kills S. aureus when these organisms are cocultured in vitro. Thus, a better understanding of P. aeruginosa-S. aureus interactions, particularly mechanisms by which these microorganisms are able to coexist in proximal physical space, will lead to better-informed treatments for chronic polymicrobial infections.

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