scholarly journals GigC, a LysR Family Transcription Regulator, Is Required for Cysteine Metabolism and Virulence in Acinetobacter baumannii

2020 ◽  
Vol 89 (1) ◽  
pp. e00180-20
Author(s):  
Michael J. Gebhardt ◽  
Daniel M. Czyz ◽  
Shweta Singh ◽  
Daniel V. Zurawski ◽  
Lev Becker ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Galleria Mellonella ◽  
Multidrug Resistant ◽  
Resistant Isolate ◽  
Infection Model ◽  
Content Type ◽  
Transcription Regulator ◽  
Nutritional Immunity ◽  
Metabolic Products ◽  
Lysr Family

ABSTRACTA critical facet of mammalian innate immunity involves the hosts’ attempts to sequester and/or limit the availability of key metabolic products from pathogens. For example, nutritional immunity encompasses host approaches to limit the availability of key heavy metal ions such as zinc and iron. Previously, we identified several hundred genes in a multidrug-resistant isolate of Acinetobacter baumannii that are required for growth and/or survival in the Galleria mellonella infection model. In the present study, we further characterize one of these genes, a LysR family transcription regulator that we previously named GigC. We show that mutant strains lacking gigC have impaired growth in the absence of the amino acid cysteine and that gigC regulates the expression of several genes involved in the sulfur assimilation and cysteine biosynthetic pathways. We further show that cells harboring a deletion of the gigC gene are attenuated in two murine infection models, suggesting that the GigC protein, likely through its regulation of the cysteine biosynthetic pathway, plays a key role in the virulence of A. baumannii.

scholarly journals Investigation of Novel pmrB and eptA Mutations in Isogenic Acinetobacter baumannii Isolates Associated with Colistin Resistance and Increased Virulence In Vivo

2019 ◽  
Vol 63 (3) ◽  
Author(s):  
Stefanie Gerson ◽  
Jonathan W. Betts ◽  
Kai Lucaßen ◽  
Carolina Silva Nodari ◽  
Julia Wille ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Lipid A ◽  
Galleria Mellonella ◽  
Resistance Mechanism ◽  
Resistant Isolate ◽  
Infection Model ◽  
Colistin Resistance ◽  
Strain Specificity ◽  
Content Type

ABSTRACT Colistin resistance in Acinetobacter baumannii is of great concern and is a threat to human health. In this study, we investigate the mechanisms of colistin resistance in four isogenic pairs of A. baumannii isolates displaying an increase in colistin MICs. A mutation in pmrB was detected in each colistin-resistant isolate, three of which were novel (A28V, I232T, and ΔL9-G12). Increased expression of pmrC was shown by semi-quantitative reverse transcription-PCR (qRT-PCR) for three colistin-resistant isolates, and the addition of phosphoethanolamine (PEtN) to lipid A by PmrC was revealed by mass spectrometry. Interestingly, PEtN addition was also observed in some colistin-susceptible isolates, indicating that this resistance mechanism might be strain specific and that other factors could contribute to colistin resistance. Furthermore, the introduction of pmrAB carrying the short amino acid deletion ΔL9-G12 into a pmrAB knockout strain resulted in increased pmrC expression and lipid A modification, but colistin MICs remained unchanged, further supporting the strain specificity of this colistin resistance mechanism. Of note, a mutation in the pmrC homologue eptA and a point mutation in ISAba1 upstream of eptA were associated with colistin resistance and increased eptA expression, which is a hitherto undescribed resistance mechanism. Moreover, no cost of fitness was observed for colistin-resistant isolates, while the virulence of these isolates was increased in a Galleria mellonella infection model. Although the mutations in pmrB were associated with colistin resistance, PEtN addition appears not to be the sole factor leading to colistin resistance, indicating that the mechanism of colistin resistance is far more complex than previously suspected and is potentially strain specific.

scholarly journals Miltefosine Reduces the Cytolytic Activity and Virulence ofAcinetobacter baumannii

2018 ◽  
Vol 63 (1) ◽  
Author(s):  
Steven E. Fiester ◽  
Brock A. Arivett ◽  
Amber C. Beckett ◽  
Benjamin R. Wagner ◽  
Emily J. Ohneck ◽  
...  
Keyword(s):  
Phospholipase C ◽  
Galleria Mellonella ◽  
Cell Damage ◽  
A549 Cells ◽  
Multidrug Resistant ◽  
Cytolytic Activity ◽  
Alveolar Epithelial Cells ◽  
Resistant Isolate ◽  
Infection Model ◽  
Content Type

ABSTRACTStagnation in antimicrobial development has led to a serious threat to public health because someAcinetobacter baumanniiinfections have become untreatable. New therapeutics with alternative mechanisms of action to combatA. baumanniiare therefore necessary to treat these infections. To this end, the virulence ofA. baumanniiisolates with various antimicrobial susceptibilities was assessed when the isolates were treated with miltefosine, a phospholipase C inhibitor. Phospholipase C activity is a contributor toA. baumanniivirulence associated with hemolysis, cytolysis of A549 human alveolar epithelial cells, and increased mortality in theGalleria mellonellaexperimental infection model. While the effects on bacterial growth were variable among strains, miltefosine treatment significantly reduced both the hemolytic and cytolytic activity of all treatedA. baumanniistrains. Additionally, scanning electron microscopy of polarized A549 cells infected with bacteria of theA. baumanniiATCC 19606Tstrain or the AB5075 multidrug-resistant isolate showed a decrease in A549 cell damage with a concomitant increase in the presence of A549 surfactant upon administration of miltefosine. The therapeutic ability of miltefosine was further supported by the results ofG. mellonellainfections, wherein miltefosine treatment of animals infected with ATCC 19606Tsignificantly decreased mortality. These data demonstrate that inhibition of phospholipase C activity results in the overall reduction ofA. baumanniivirulence in bothin vitroandin vivomodels, making miltefosine a viable option for the treatment ofA. baumanniiinfections, particularly those caused by multidrug-resistant isolates.

scholarly journals In VitroandIn VivoAntimicrobial Activities of Gallium Nitrate against Multidrug-Resistant Acinetobacter baumannii

2012 ◽  
Vol 56 (11) ◽  
pp. 5961-5970 ◽  
Author(s):  
Luísa C. S. Antunes ◽  
Francesco Imperi ◽  
Fabrizia Minandri ◽  
Paolo Visca
Keyword(s):  
Human Serum ◽  
Acinetobacter Baumannii ◽  
Galleria Mellonella ◽  
Therapeutic Potential ◽  
Survival Rates ◽  
Bloodstream Infections ◽  
Multidrug Resistant ◽  
Gallium Nitrate ◽  
Content Type ◽  
Bacterial Physiology

ABSTRACTMultidrug-resistantAcinetobacter baumanniiposes a tremendous challenge to traditional antibiotic therapy. Due to the crucial role of iron in bacterial physiology and pathogenicity, we investigated iron metabolism as a possible target for anti-A. baumanniichemotherapy using gallium as an iron mimetic. Due to chemical similarity, gallium competes with iron for binding to several redox enzymes, thereby interfering with a number of essential biological reactions. We found that Ga(NO3)3, the active component of an FDA-approved drug (Ganite), inhibits the growth of a collection of 58A. baumanniistrains in both chemically defined medium and human serum, at concentrations ranging from 2 to 80 μM and from 4 to 64 μM, respectively. Ga(NO3)3delayed the entry ofA. baumanniiinto the exponential phase and drastically reduced bacterial growth rates. Ga(NO3)3activity was strongly dependent on iron availability in the culture medium, though the mechanism of growth inhibition was independent of dysregulation of gene expression controlled by the ferric uptake regulator Fur. Ga(NO3)3also protectedGalleria mellonellalarvae from lethalA. baumanniiinfection, with survival rates of ≥75%. At therapeutic concentrations for humans (28 μM plasma levels), Ga(NO3)3inhibited the growth in human serum of 76% of the multidrug-resistantA. baumanniiisolates tested by ≥90%, raising expectations on the therapeutic potential of gallium for the treatment ofA. baumanniibloodstream infections. Ga(NO3)3also showed strong synergism with colistin, suggesting that a colistin-gallium combination holds promise as a last-resort therapy for infections caused by pan-resistantA. baumannii.

scholarly journals Characterization of RelA in Acinetobacter baumannii

2020 ◽  
Vol 202 (12) ◽  
Author(s):  
María Pérez-Varela ◽  
Aimee R. P. Tierney ◽  
Ju-Sim Kim ◽  
Andrés Vázquez-Torres ◽  
Philip Rather
Keyword(s):  
Acinetobacter Baumannii ◽  
Galleria Mellonella ◽  
Multidrug Resistant ◽  
Cell Physiology ◽  
Content Type ◽  
Content Model ◽  
Transposon Insertion ◽  
Downstream Effectors

ABSTRACT In response to nutrient depletion, the RelA and SpoT proteins generate the signaling molecule (p)ppGpp, which then controls a number of downstream effectors to modulate cell physiology. In Acinetobacter baumannii strain AB5075, a relA ortholog (ABUW_3302) was identified by a transposon insertion that conferred an unusual colony phenotype. An in-frame deletion in relA (ΔrelA) failed to produce detectable levels of ppGpp when amino acid starvation was induced with serine hydroxamate. The ΔrelA mutant was blocked from switching from the virulent opaque colony variant (VIR-O) to the avirulent translucent colony variant (AV-T), but the rate of AV-T to VIR-O switching was unchanged. In addition, the ΔrelA mutation resulted in a pronounced hypermotile phenotype on 0.35% agar plates. This hypermotility was dependent on the activation of a LysR regulator ABUW_1132, which was required for expression of AbaR, a LuxR family quorum-sensing regulator. In the ΔrelA mutant, ABUW_1132 was also required for the increased expression of an operon composed of the ABUW_3766-ABUW_3773 genes required for production of the surfactant-like lipopeptide acinetin 505. Additional phenotypes identified in the ΔrelA mutant included (i) cell elongation at high density, (ii) reduced formation of persister cells tolerant to colistin and rifampin, and (iii) decreased virulence in a Galleria mellonella model. IMPORTANCE Acinetobacter baumannii is a pathogen of worldwide importance. Due to the increasing prevalence of antibiotic resistance, these infections are becoming increasingly difficult to treat. New therapies are required to combat multidrug-resistant isolates. The role of RelA in A. baumannii is largely unknown. This study demonstrates that like in other bacteria, RelA controls a variety of functions, including virulence. Strategies to inhibit the activity of RelA and the resulting production of ppGpp could inhibit virulence and may represent a new therapeutic approach.

scholarly journals Efficacy of Apramycin against Multidrug-Resistant Acinetobacter baumannii in the Murine Neutropenic Thigh Model

2018 ◽  
Vol 62 (4) ◽  
Author(s):  
Anthony D. Kang ◽  
Kenneth P. Smith ◽  
Anders H. Berg ◽  
Katherine A. Truelson ◽  
George M. Eliopoulos ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Maximum Concentration ◽  
Area Under The Curve ◽  
Multidrug Resistant ◽  
Infection Model ◽  
Gram Negative ◽  
Content Type ◽  
Model Treatment

ABSTRACT Apramycin, an aminocyclitol aminoglycoside, was rapidly bactericidal against Acinetobacter baumannii . In a neutropenic murine thigh infection model, treatment-associated A. baumannii CFU reductions of >4 log 10 per thigh were observed for all exposures for which area under the curve (AUC)/MIC ratio was >50 and maximum concentration of drug in serum ( C max )/MIC was ≈10 or higher. Based on these findings, we suggest that apramycin deserves further preclinical exploration as a repurposed therapeutic for multidrug-resistant Gram-negative pathogens, including A. baumannii .

scholarly journals The Acinetobacter baumannii Znu System Overcomes Host-Imposed Nutrient Zinc Limitation

2019 ◽  
Vol 87 (12) ◽  
Author(s):  
Laura E. Hesse ◽  
Zachery R. Lonergan ◽  
William N. Beavers ◽  
Eric P. Skaar
Keyword(s):  
Acinetobacter Baumannii ◽  
Defense Mechanisms ◽  
Pathogenic Bacteria ◽  
Bacterial Pathogen ◽  
Multidrug Resistant ◽  
World Health ◽  
Content Type ◽  
Nutritional Immunity ◽  
Essential Nutrient ◽  
Health Organization

ABSTRACT Acinetobacter baumannii is an opportunistic bacterial pathogen capable of causing a variety of infections, including pneumonia, sepsis, wound, and burn infections. A. baumannii is an increasing threat to public health due to the prevalence of multidrug-resistant strains, leading the World Health Organization to declare A. baumannii a “Priority 1: Critical” pathogen, for which the development of novel antimicrobials is desperately needed. Zinc (Zn) is an essential nutrient that pathogenic bacteria, including A. baumannii, must acquire from their hosts in order to survive. Consequently, vertebrate hosts have defense mechanisms to sequester Zn from invading bacteria through a process known as nutritional immunity. Here, we describe a Zn uptake (Znu) system that enables A. baumannii to overcome this host-imposed Zn limitation. The Znu system consists of an inner membrane ABC transporter and an outer membrane TonB-dependent receptor. Strains of A. baumannii lacking any individual Znu component are unable to grow in Zn-starved conditions, including in the presence of the host nutritional immunity protein calprotectin. The Znu system contributes to Zn-limited growth by aiding directly in the uptake of Zn into A. baumannii cells and is important for pathogenesis in murine models of A. baumannii infection. These results demonstrate that the Znu system allows A. baumannii to subvert host nutritional immunity and acquire Zn during infection.

scholarly journals Protective Effect of a Synbiotic against Multidrug-Resistant Acinetobacter baumannii in a Murine Infection Model

2016 ◽  
Vol 60 (5) ◽  
pp. 3041-3050 ◽  
Author(s):  
Takashi Asahara ◽  
Akira Takahashi ◽  
Norikatsu Yuki ◽  
Rumi Kaji ◽  
Takuya Takahashi ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Acinetobacter Baumannii ◽  
Multidrug Resistant ◽  
Additional Treatment ◽  
Indigenous Populations ◽  
Sublethal Dose ◽  
Infection Model ◽  
Content Type ◽  
Multidrug Resistant Bacterium ◽  
Positive Correlations

ABSTRACTThis study investigated the ability of the probioticBifidobacterium brevestrain Yakult (BbY) to protect against infection, as well as the potentiation of BbY activity by the synbiotic combination of BbY and prebiotic galactooligosaccharides (GOS). The study employed a mouse model of lethal intestinal multidrug-resistantAcinetobacter baumannii(MDRAb) infection. The endogenous intestinal microbiota was disrupted by the administration of multiple antibiotics, causing the loss of endogenousBifidobacterium. Oral infection of these mice with MDRAb resulted in marked growth of this organism. Additional treatment of the infected mice with a sublethal dose of 5-fluorouracil (5-FU) induced systemic invasion by MDRAb and subsequent animal death. The continuous oral administration of BbY increased the survival rate and inhibited the intestinal growth and invasion by MDRAb in the infection model. Disruptions of the intestinal environment and barrier function in the infected mice were attenuated by BbY. Protection against the MDRAb infection was markedly potentiated by a synbiotic combination of BbY and GOS, although GOS by itself did not provide protection. Negative correlations were observed between intestinal MDRAb and BbY counts or acetic acid levels; positive correlations were observed between acetic acid levels and intestinal epithelium expression of tight-junction-related genes. These results demonstrated that the probiotic and synbiotic markedly potentiated protection against fatal intestinal infection caused by a multidrug-resistant bacterium. Probiotics and synbiotics are presumed to provide protection by compensation for the disrupted indigenous populations, thereby maintaining the intestinal environments and barrier functions otherwise targeted during opportunistic infection by MDRAb.

scholarly journals CsrA Supports both Environmental Persistence and Host-Associated Growth of Acinetobacter baumannii

2020 ◽  
Vol 88 (12) ◽  
Author(s):  
John M. Farrow ◽  
Greg Wells ◽  
Samantha Palethorpe ◽  
Mark D. Adams ◽  
Everett C. Pesci
Keyword(s):  
Acinetobacter Baumannii ◽  
Galleria Mellonella ◽  
Bacterial Pathogen ◽  
Multidrug Resistant ◽  
Growth Defect ◽  
Gene Encoding ◽  
Content Type ◽  
Indirect Transmission ◽  
Mutant Strains ◽  
Carbon Storage Regulator

ABSTRACT Acinetobacter baumannii is an opportunistic and frequently multidrug-resistant Gram-negative bacterial pathogen that primarily infects critically ill individuals. Indirect transmission from patient to patient in hospitals can drive infections, supported by this organism’s abilities to persist on dry surfaces and rapidly colonize susceptible individuals. To investigate how A. baumannii survives on surfaces, we cultured A. baumannii in liquid media for several days and then analyzed isolates that lost the ability to survive drying. One of these isolates carried a mutation that affected the gene encoding the carbon storage regulator CsrA. As we began to examine the role of CsrA in A. baumannii, we observed that the growth of ΔcsrA mutant strains was inhibited in the presence of amino acids. The ΔcsrA mutant strains had a reduced ability to survive drying and to form biofilms but an improved ability to tolerate increased osmolarity compared with the wild type. We also examined the importance of CsrA for A. baumannii virulence. The ΔcsrA mutant strains had a greatly reduced ability to kill Galleria mellonella larvae, could not replicate in G. mellonella hemolymph, and also had a growth defect in human serum. Together, these results show that CsrA is essential for the growth of A. baumannii on host-derived substrates and is involved in desiccation tolerance, implying that CsrA controls key functions involved in the transmission of A. baumannii in hospitals.

scholarly journals Rapid Killing of Acinetobacter baumannii by Polymyxins Is Mediated by a Hydroxyl Radical Death Pathway

2012 ◽  
Vol 56 (11) ◽  
pp. 5642-5649 ◽  
Author(s):  
Timothy R. Sampson ◽  
Xiang Liu ◽  
Max R. Schroeder ◽  
Colleen S. Kraft ◽  
Eileen M. Burd ◽  
...  
Keyword(s):  
Hydroxyl Radical ◽  
Acinetobacter Baumannii ◽  
Opportunistic Pathogen ◽  
Multidrug Resistant ◽  
Clinical Isolates ◽  
Resistant Isolate ◽  
Alternative Mechanism ◽  
Content Type ◽  
Radical Production ◽  
Clinically Significant

ABSTRACTAcinetobacter baumanniiis an opportunistic pathogen that is a cause of clinically significant nosocomial infections. Increasingly, clinical isolates ofA. baumanniiare extensively resistant to numerous antibiotics, and the use of polymyxin antibiotics against these infections is often the final treatment option. Historically, the polymyxins have been thought to kill bacteria through membrane lysis. Here, we present an alternative mechanism based on data demonstrating that polymyxins induce rapid cell death through hydroxyl radical production. Supporting this notion, we found that inhibition of radical production delays the ability of polymyxins to killA. baumannii. Notably, we demonstrate that this mechanism of killing occurs in multidrug-resistant clinical isolates ofA. baumanniiand that this response is not induced in a polymyxin-resistant isolate. This study is the first to demonstrate that polymyxins induce rapid killing ofA. baumanniiand other Gram-negatives through hydroxyl radical production. This significantly augments our understanding of the mechanism of polymyxin action, which is critical knowledge toward the development of adjunctive therapies, particularly given the increasing necessity for treatment with these antibiotics in the clinical setting.

scholarly journals Antimicrobial Activity of Gallium Protoporphyrin IX against Acinetobacter baumannii Strains Displaying Different Antibiotic Resistance Phenotypes

2015 ◽  
Vol 59 (12) ◽  
pp. 7657-7665 ◽  
Author(s):  
Brock A. Arivett ◽  
Steven E. Fiester ◽  
Emily J. Ohneck ◽  
William F. Penwell ◽  
Cynthia M. Kaufman ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Galleria Mellonella ◽  
Therapeutic Option ◽  
Protoporphyrin Ix ◽  
Multidrug Resistant ◽  
Content Type ◽  
Antibiotic Development ◽  
Alveolar Epithelial ◽  
Mueller Hinton ◽  
Novel Therapeutic Strategies

ABSTRACTA paucity of effective, currently available antibiotics and a lull in antibiotic development pose significant challenges for treatment of patients with multidrug-resistant (MDR)Acinetobacter baumanniiinfections. Thus, novel therapeutic strategies must be evaluated to meet the demands of treatment of these often life-threatening infections. Accordingly, we examined the antibiotic activity of gallium protoporphyrin IX (Ga-PPIX) against a collection ofA. baumanniistrains, including nonmilitary and military strains and strains representing different clonal lineages and isolates classified as susceptible or MDR. Susceptibility testing demonstrated that Ga-PPIX inhibits the growth of all tested strains when cultured in cation-adjusted Mueller-Hinton broth, with a MIC of 20 μg/ml. This concentration significantly reduced bacterial viability, while 40 μg/ml killed all cells of theA. baumanniiATCC 19606Tand ACICU MDR isolate after 24-h incubation. Recovery of ATCC 19606Tand ACICU strains from infected A549 human alveolar epithelial monolayers was also decreased when the medium was supplemented with Ga-PPIX, particularly at a 40-μg/ml concentration. Similarly, the coinjection of bacteria with Ga-PPIX increased the survival ofGalleria mellonellalarvae infected with ATCC 19606Tor ACICU. Ga-PPIX was cytotoxic only when monolayers or larvae were exposed to concentrations 16-fold and 1,250-fold higher than those showing antibacterial activity, respectively. These results indicate that Ga-PPIX could be a viable therapeutic option for treatment of recalcitrantA. baumanniiinfections regardless of the resistance phenotype, clone lineage, time and site of isolation of strains causing these infections and their iron uptake phenotypes or the iron content of the media.

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