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 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 Phospholipase C of Cryptococcus neoformans Regulates Homeostasis and Virulence by Providing Inositol Trisphosphate as a Substrate for Arg1 Kinase

2013 ◽  
Vol 81 (4) ◽  
pp. 1245-1255 ◽  
Author(s):  
Sophie Lev ◽  
Desmarini Desmarini ◽  
Cecilia Li ◽  
Methee Chayakulkeeree ◽  
Ana Traven ◽  
...  
Keyword(s):  
Cryptococcus Neoformans ◽  
Phospholipase C ◽  
Mammalian Cells ◽  
Galleria Mellonella ◽  
Inositol Trisphosphate ◽  
Infection Model ◽  
Inositol Polyphosphate ◽  
Inositol Polyphosphates ◽  
Content Type ◽  
Capsule Production

ABSTRACTPhospholipase C (PLC) ofCryptococcus neoformans(CnPlc1) is crucial for virulence of this fungal pathogen. To investigate the mechanism of CnPlc1-mediated signaling, we established that phosphatidylinositol 4,5-bisphosphate (PIP2) is a major CnPlc1 substrate, which is hydrolyzed to produce inositol trisphosphate (IP3). InSaccharomyces cerevisiae, Plc1-derived IP3is a substrate for the inositol polyphosphate kinase Arg82, which converts IP3to more complex inositol polyphosphates. In this study, we show that inC. neoformans, the enzyme encoded byARG1is the major IP3kinase, and we further demonstrate that catalytic activity of Arg1 is essential for cellular homeostasis and virulence in theGalleria mellonellainfection model. IP3content was reduced in the CnΔplc1mutant and markedly increased in the CnΔarg1mutant, while PIP2was increased in both mutants. The CnΔplc1and CnΔarg1mutants shared significant phenotypic similarity, including impaired thermotolerance, compromised cell walls, reduced capsule production and melanization, defective cell separation, and the inability to form mating filaments. In contrast to theS. cerevisiae ARG82deletion mutant (ScΔarg82) strain, the CnΔarg1mutant exhibited dramatically enlarged vacuoles indicative of excessive vacuolar fusion. In mammalian cells, PLC-derived IP3causes Ca2+release and calcineurin activation. Our data show that, unlike mammalian PLCs, CnPlc1 does not contribute significantly to calcineurin activation. Collectively, our findings provide the first evidence that the inositol polyphosphate anabolic pathway is essential for virulence ofC. neoformansand further show that production of IP3as a precursor for synthesis of more complex inositol polyphosphates is the key biochemical function of CnPlc1.

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 ThemtfATranscription Factor Gene Controls Morphogenesis, Gliotoxin Production, and Virulence in the Opportunistic Human Pathogen Aspergillus fumigatus

2014 ◽  
Vol 13 (6) ◽  
pp. 766-775 ◽  
Author(s):  
Timothy D. Smith ◽  
Ana M. Calvo
Keyword(s):  
Aspergillus Fumigatus ◽  
Protease Activity ◽  
Galleria Mellonella ◽  
Molecular Genetic ◽  
Colony Growth ◽  
Infection Model ◽  
Slight Reduction ◽  
Wild Type ◽  
Content Type ◽  
Factor Gene

ABSTRACTAspergillus fumigatusis the leading causative agent of invasive aspergillosis (IA). The number of cases is on the rise, with mortality rates as high as 90% among immunocompromised patients. Molecular genetic studies inA. fumigatuscould provide novel targets to potentially set the basis for antifungal therapies. In the current study, we investigated the role of the transcription factor genemtfAinA. fumigatus. Our results revealed thatmtfAplays a role in the growth and development of the fungus. Deletion or overexpression ofmtfAleads to a slight reduction in colony growth, as well as a reduction in conidiation levels, in the overexpression strain compared to the wild-type strain. Furthermore, production of the secondary metabolite gliotoxin increased whenmtfAwas overexpressed, coinciding with an increase in the transcription levels of the gliotoxin genesgliZandgliPwith respect to the wild type. In addition, our study showed thatmtfAis also necessary for normal protease activity inA. fumigatus; deletion ofmtfAresulted in a reduction of protease activity compared to wild-type levels. Importantly, the absence ofmtfAcaused a decrease in virulence in theGalleria mellonellainfection model, indicating thatmtfAis necessary forA. fumigatuswild-type pathogenesis.

scholarly journals A Light-Regulated Type I Pilus Contributes toAcinetobacter baumanniiBiofilm, Motility, and Virulence Functions

2018 ◽  
Vol 86 (9) ◽  
Author(s):  
Cecily R. Wood ◽  
Emily J. Ohneck ◽  
Richard E. Edelmann ◽  
Luis A. Actis
Keyword(s):  
Biofilm Formation ◽  
Galleria Mellonella ◽  
Alveolar Epithelial Cells ◽  
Ecological Niches ◽  
Type I ◽  
Pellicle Formation ◽  
Content Type ◽  
Alveolar Epithelial ◽  
Abiotic Surfaces ◽  
Cells Cultured

ABSTRACTTranscriptional analyses ofAcinetobacter baumanniiATCC 17978 showed that the expression of A1S_2091 was enhanced in cells cultured in darkness at 24°C through a process that depended on the BlsA photoreceptor. Disruption of A1S_2091, a component of the A1S_2088-A1S_2091 polycistronic operon predicted to code for a type I chaperone/usher pilus assembly system, abolished surface motility and pellicle formation but significantly enhanced biofilm formation on plastic by bacteria cultured in darkness. Based on these observations, the A1S_2088-A1S_2091 operon was named thephotoregulatedpilus ABCD (prpABCD) operon, with A1S_2091 coding for the PrpA pilin subunit. Unexpectedly, comparative analyses of ATCC 17978 andprpAisogenic mutant cells cultured at 37°C showed the expression of light-regulated biofilm biogenesis and motility functions under a temperature condition that drastically affects BlsA production and its light-sensing activity. These assays also suggest that ATCC 17978 cells produce alternative light-regulated adhesins and/or pilus systems that enhance bacterial adhesion and biofilm formation at both 24°C and 37°C on plastic as well as on the surface of polarized A549 alveolar epithelial cells, where the formation of bacterial filaments and cell chains was significantly enhanced. The inactivation ofprpAalso resulted in a significant reduction in virulence when tested by using theGalleria mellonellavirulence model. All these observations provide strong evidence showing the capacity ofA. baumanniito sense light and interact with biotic and abiotic surfaces using undetermined alternative sensing and regulatory systems as well as alternative adherence and motility cellular functions that allow this pathogen to persist in different ecological niches.

scholarly journals Activity of Telavancin against Staphylococcus aureus Isolates, Including Those with Decreased Susceptibility to Ceftaroline, from Cystic Fibrosis Patients

2018 ◽  
Vol 62 (9) ◽  
Author(s):  
Melanie Roch ◽  
Maria Celeste Varela ◽  
Agustina Taglialegna ◽  
Warren E. Rose ◽  
Adriana E. Rosato
Keyword(s):  
Cystic Fibrosis ◽  
Staphylococcus Aureus ◽  
Galleria Mellonella ◽  
Therapeutic Option ◽  
The United States ◽  
Infection Model ◽  
Content Type ◽  
Complicated Skin ◽  
Hospital Acquired

ABSTRACT Methicillin-resistant Staphylococcus aureus (MRSA) acquisition in cystic fibrosis (CF) patients confers a clinical outcome worse than that in non-CF patients with an increased rate of declined lung function. Telavancin, an approved lipoglycopeptide used to treat infections due to S. aureus, has a dual mode of action causing inhibition of peptidoglycan synthesis and membrane depolarization. MRSA infections in CF patients remain an important problem with no foreseeable decline in prevalence rates. Although telavancin is currently in clinical use for the treatment of complicated skin infections and hospital-acquired pneumonia, the activity against S. aureus infections in CF patients has not been investigated. In this work, we studied the activity of telavancin against CF patient-derived S. aureus strains collected from geographically diverse CF centers in the United States. We found that the telavancin MIC90 was 0.06 μg/ml, 8-fold lower than the ceftaroline or daptomycin MIC90 and 25-fold lower than the linezolid and vancomycin MIC90. We demonstrate that telavancin at serum free concentrations has rapid bactericidal activity, with a decrease of more than 3 log10 CFU/ml being achieved during the first 4 to 6 h of treatment, performing better in this assay than vancomycin and ceftaroline, including against S. aureus strains resistant to ceftaroline. Telavancin resistance was infrequent (0.3%), although we found that it can occur in vitro in both CF- and non-CF patient-derived S. aureus strains by progressive passages with subinhibitory concentrations. Genetic analysis of telavancin-resistant in vitro mutants showed gene polymorphisms in cell wall and virulence genes and increased survival in a Galleria mellonella infection model. Thus, we conclude that telavancin represents a promising therapeutic option for infections in CF patients with potent in vitro activity and a low resistance development potential.

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 Proof-of-Principle Study in a Murine Lung Infection Model of Antipseudomonal Activity of Phage PEV20 in a Dry-Powder Formulation

2017 ◽  
Vol 62 (2) ◽  
Author(s):  
Rachel Yoon Kyung Chang ◽  
Ke Chen ◽  
Jiping Wang ◽  
Martin Wallin ◽  
Warwick Britton ◽  
...  
Keyword(s):  
Lung Infection ◽  
Treated Group ◽  
Multidrug Resistant ◽  
Resistant Bacteria ◽  
Infection Model ◽  
Dry Powder ◽  
Intratracheal Administration ◽  
Promising Alternative ◽  
Content Type ◽  
Powder Formulation

ABSTRACT Bacteriophage therapy is a promising alternative treatment to antibiotics, as it has been documented to be efficacious against multidrug-resistant bacteria with minimal side effects. Several groups have demonstrated the efficacy of phage suspension in vivo to treat lung infections using intranasal delivery; however, phage dry-powder administration to the lungs has not yet been explored. Powder formulations provide potential advantages over a liquid formulation, including easy storage, transport, and administration. The purpose of this study was to assess the bactericidal activities of phage dry-powder formulations against multidrug-resistant (MDR) strain Pseudomonas aeruginosa FADDI-PA001 in a mouse lung infection model. Phage PEV20 spray dried with lactose and leucine produced an inhalable powder at a concentration of 2 × 107 PFU/mg. P. aeruginosa lung infection was established by intratracheal administration of the bacterial suspension to neutropenic mice. At 2 h after the bacterial challenge, the infected mice were treated with 2 mg of the phage powder using a dry-powder insufflator. At 24 h after the phage treatment, the bacterial load in the lungs was decreased by 5.3 log10 (P < 0.0005) in the phage-treated group compared with that in the nontreated group. Additionally, the phage concentration in the lungs was increased by 1 log10 at 24 h in the treated group. These results demonstrate the feasibility of a pulmonary delivery of phage PEV20 dry-powder formulation for the treatment of lung infection caused by antibiotic-resistant P. aeruginosa.

scholarly journals Optimization of Synergistic Combination Regimens against Carbapenem- and Aminoglycoside-Resistant Clinical Pseudomonas aeruginosa Isolates via Mechanism-Based Pharmacokinetic/Pharmacodynamic Modeling

2016 ◽  
Vol 61 (1) ◽  
Author(s):  
Rajbharan Yadav ◽  
Jürgen B. Bulitta ◽  
Roger L. Nation ◽  
Cornelia B. Landersdorfer
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Multidrug Resistant ◽  
Viable Count ◽  
Resistant Isolate ◽  
Pharmacodynamic Modeling ◽  
Combination Regimen ◽  
Bacterial Killing ◽  
Content Type ◽  
Dosage Regimens ◽  
Combination Regimens

ABSTRACT Optimizing antibiotic combinations is promising to combat multidrug-resistant Pseudomonas aeruginosa. This study aimed to systematically evaluate synergistic bacterial killing and prevention of resistance by carbapenem and aminoglycoside combinations and to rationally optimize combination dosage regimens via a mechanism-based mathematical model (MBM). We studied monotherapies and combinations of imipenem with tobramycin or amikacin against three difficult-to-treat double-resistant clinical P. aeruginosa isolates. Viable-count profiles of total and resistant populations were quantified in 48-h static-concentration time-kill studies (inoculum, 107.5 CFU/ml). We rationally optimized combination dosage regimens via MBM and Monte Carlo simulations against isolate FADDI-PA088 (MIC of imipenem [MICimipenem] of 16 mg/liter and MICtobramycin of 32 mg/liter, i.e., both 98th percentiles according to the EUCAST database). Against this isolate, imipenem (1.5× MIC) combined with 1 to 2 mg/liter tobramycin (MIC, 32 mg/liter) or amikacin (MIC, 4 mg/liter) yielded ≥2-log10 more killing than the most active monotherapy at 48 h and prevented resistance. For all three strains, synergistic killing without resistance was achieved by ≥0.88× MICimipenem in combination with a median of 0.75× MICtobramycin (range, 0.032× to 2.0× MICtobramycin) or 0.50× MICamikacin (range, 0.25× to 0.50× MICamikacin). The MBM indicated that aminoglycosides significantly enhanced the imipenem target site concentration up to 3-fold; achieving 50% of this synergistic effect required aminoglycoside concentrations of 1.34 mg/liter (if the aminoglycoside MIC was 4 mg/liter) and 4.88 mg/liter (for MICs of 8 to 32 mg/liter). An optimized combination regimen (continuous infusion of imipenem at 5 g/day plus a 0.5-h infusion with 7 mg/kg of body weight tobramycin) was predicted to achieve >2.0-log10 killing and prevent regrowth at 48 h in 90.3% of patients (median bacterial killing, >4.0 log10 CFU/ml) against double-resistant isolate FADDI-PA088 and therefore was highly promising.

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