Effect of Incubation Temperature on Antibiotic Resistance and Virulence Factors of Acinetobacter baumannii ATCC 17978

ABSTRACT Acinetobacter baumannii is a notorious opportunistic pathogen that is prevalent mainly in hospital settings. The ability of A. baumannii to adapt and to survive in a range of environments has been a key factor for its persistence and success as an opportunistic pathogen. In this study, we investigated the effect of temperature on the clinically relevant phenotypes displayed by A. baumannii at 37°C and 28°C. Surface-associated motility was significantly reduced at 28°C, while biofilm formation on plastic surfaces was increased at 28°C. Decreased susceptibility to aztreonam and increased susceptibility to trimethoprim-sulfamethoxazole were observed at 28°C. No differences in virulence, as assayed in a Galleria mellonella model, were observed. Proteomic analysis showed differential expression of 629 proteins, of which 366 were upregulated and 263 were downregulated at 28°C. Upregulation of the Csu and iron uptake proteins at 28°C was a key finding for understanding some of the phenotypes displayed by A. baumannii at 28°C.

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Characterization of RelA in Acinetobacter baumannii

Journal of Bacteriology ◽

10.1128/jb.00045-20 ◽

2020 ◽

Vol 202 (12) ◽

Cited By ~ 3

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.

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Pathogenicity of Clinical Acinetobacter baumannii Isolates in a Galleria mellonella Host Model According toblaOXA-40Gene and Epidemiological Outbreak Status

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02201-13 ◽

2013 ◽

Vol 58 (2) ◽

pp. 1240-1242 ◽

Cited By ~ 5

Author(s):

John S. Esterly ◽

Milena M. McLaughlin ◽

Michael Malczynski ◽

Chao Qi ◽

Teresa R. Zembower ◽

...

Keyword(s):

Acinetobacter Baumannii ◽

Patient Outcomes ◽

Clinical Studies ◽

Galleria Mellonella ◽

Content Type ◽

Content Model ◽

Carbapenem Resistant ◽

Poor Patient

ABSTRACTClinical studies have suggested thatblaOXA-40-positiveAcinetobacter baumanniiisolates are associated with poor patient outcomes; however, reasons for unfavorable outcomes are difficult to discern in clinical studies. The objective of this study was to assess the virulence of carbapenem-resistantA. baumanniiaccording toblaOXA-40and epidemiological outbreak status in aGalleria mellonellamodel. Eight isolates ofA. baumanniiwere studied. Nonoutbreak isolates andblaOXA-40-negative isolates more rapidly killed infectedG. mellonella(P< 0.01).

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Lon Protease Has Multifaceted Biological Functions inAcinetobacter baumannii

Journal of Bacteriology ◽

10.1128/jb.00536-18 ◽

2018 ◽

Vol 201 (2) ◽

Cited By ~ 5

Author(s):

Carly Ching ◽

Brendan Yang ◽

Chineme Onwubueke ◽

David Lazinski ◽

Andrew Camilli ◽

...

Keyword(s):

Acinetobacter Baumannii ◽

Biofilm Formation ◽

Developmental Process ◽

Cell Envelope ◽

Opportunistic Pathogen ◽

Lon Protease ◽

Content Type ◽

Hospital Acquired Infections ◽

Biofilm Development ◽

Hospital Acquired

ABSTRACTAcinetobacter baumanniiis a Gram-negative opportunistic pathogen that is known to survive harsh environmental conditions and is a leading cause of hospital-acquired infections. Specifically, multicellular communities (known as biofilms) ofA. baumanniican withstand desiccation and survive on hospital surfaces and equipment. Biofilms are bacteria embedded in a self-produced extracellular matrix composed of proteins, sugars, and/or DNA. Bacteria in a biofilm are protected from environmental stresses, including antibiotics, which provides the bacteria with selective advantage for survival. Although some gene products are known to play roles in this developmental process inA. baumannii, mechanisms and signaling remain mostly unknown. Here, we find that Lon protease inA. baumanniiaffects biofilm development and has other important physiological roles, including motility and the cell envelope. Lon proteases are found in all domains of life, participating in regulatory processes and maintaining cellular homeostasis. These data reveal the importance of Lon protease in influencing keyA. baumanniiprocesses to survive stress and to maintain viability.IMPORTANCEAcinetobacter baumanniiis an opportunistic pathogen and is a leading cause of hospital-acquired infections.A. baumanniiis difficult to eradicate and to manage, because this bacterium is known to robustly survive desiccation and to quickly gain antibiotic resistance. We sought to investigate biofilm formation inA. baumannii, since much remains unknown about biofilm formation in this bacterium. Biofilms, which are multicellular communities of bacteria, are surface attached and difficult to eliminate from hospital equipment and implanted devices. Our research identifies multifaceted physiological roles for the conserved bacterial protease Lon inA. baumannii. These roles include biofilm formation, motility, and viability. This work broadly affects and expands understanding of the biology ofA. baumannii, which will permit us to find effective ways to eliminate the bacterium.

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

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01519-12 ◽

2012 ◽

Vol 56 (11) ◽

pp. 5961-5970 ◽

Cited By ~ 72

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.

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Pseudomonas aeruginosa-Mediated Damage Requires Distinct Receptors at the Apical and Basolateral Surfaces of the Polarized Epithelium

Infection and Immunity ◽

10.1128/iai.01215-09 ◽

2009 ◽

Vol 78 (3) ◽

pp. 939-953 ◽

Cited By ~ 36

Author(s):

Iwona Bucior ◽

Keith Mostov ◽

Joanne N. Engel

Keyword(s):

Pseudomonas Aeruginosa ◽

Mdck Cells ◽

Three Dimensional ◽

Opportunistic Pathogen ◽

Necessary And Sufficient ◽

Plastic Surfaces ◽

Pharmacologic Inhibition ◽

Increased Susceptibility ◽

Polarized Epithelium

ABSTRACT Pseudomonas aeruginosa, an important opportunistic pathogen of humans, exploits epithelial damage to establish infection. We have rigorously explored the role of N-glycoproteins and heparan sulfate proteoglycans (HSPGs) in P. aeruginosa-mediated attachment and subsequent downstream events at the apical (AP) and basolateral (BL) surfaces of polarized epithelium. We demonstrate that the N-glycan chains at the AP surface are necessary and sufficient for binding, invasion, and cytotoxicity to kidney (MDCK) and airway (Calu-3) cells grown at various states of polarization on Transwell filters. Upregulation of N-glycosylation enhanced binding, whereas pharmacologic inhibition of N-glycosylation or infection of MDCK cells defective in N-glycosylation resulted in decreased binding. In contrast, at the BL surface, the HS moiety of HSPGs mediated P. aeruginosa binding, cytotoxicity, and invasion. In incompletely polarized epithelium, HSPG abundance was increased at the AP surface, explaining its increased susceptibility to P. aeruginosa colonization and damage. Using MDCK cells grown as three-dimensional cysts as a model for epithelial organs, we show that P. aeruginosa specifically colocalized with HS-rich areas at the BL membrane but with complex N-glycans at the AP surface. Finally, P. aeruginosa bound to HS chains and N-glycans coated on plastic surfaces, showing the highest binding affinity toward isolated HS chains. Together, these findings demonstrate that P. aeruginosa recognizes distinct receptors on the AP and BL surfaces of polarized epithelium. Changes in the composition of N-glycan chains and/or in the distribution of HSPGs may explain the enhanced susceptibility of damaged epithelium to P. aeruginosa.

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Candida guilliermondii Complex Is Characterized by High Antifungal Resistance but Low Mortality in 22 Cases of Candidemia

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00099-17 ◽

2017 ◽

Vol 61 (7) ◽

Cited By ~ 13

Author(s):

Laura Judith Marcos-Zambrano ◽

Mireia Puig-Asensio ◽

Felipe Pérez-García ◽

Pilar Escribano ◽

Carlos Sánchez-Carrillo ◽

...

Keyword(s):

Metabolic Activity ◽

Biofilm Formation ◽

Galleria Mellonella ◽

Sensu Stricto ◽

Candida Guilliermondii ◽

Molecular Techniques ◽

Content Type ◽

Content Model ◽

Crystal Violet Assay

ABSTRACT The objectives of our study were to describe the characteristics of patients with Candida guilliermondii candidemia and to perform an in-depth microbiological characterization of isolates and compare them with those of patients with C. albicans candidemia. We described the risk factors and outcomes of 22 patients with candidemia caused by the C. guilliermondii complex. Incident isolates were identified using molecular techniques, and susceptibility to fluconazole, anidulafungin, and micafungin was studied. Biofilm formation was measured using the crystal violet assay (biomass production) and the XTT reduction assay (metabolic activity), and virulence was studied using the Galleria mellonella model. Biofilm formation was compared with that observed for C. albicans. The main conditions predisposing to infection were malignancy (68%), immunosuppressive therapy (59%), and neutropenia (18%). Clinical presentation of candidemia was less severe in patients infected by the C. guilliermondii complex than in patients infected by C. albicans, and 30-day mortality was lower in C. guilliermondii patients (13.6% versus 33.9%, respectively; P = 0.049). Isolates were identified as C. guilliermondii sensu stricto (n = 17) and Candida fermentati (n = 5). The isolates produced biofilms with low metabolic activity and moderate biomass. The G. mellonella model showed that C. guilliermondii was less virulent than C. albicans (mean of 6 days versus 1 day of survival, respectively; P < 0.001). Patients with candidemia caused by the C. guilliermondii complex had severe and debilitating underlying conditions. Overall, the isolates showed diminished susceptibility to fluconazole and echinocandins, although poor biofilm formation and the low virulence were associated with a favorable outcome.

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

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01586-18 ◽

2019 ◽

Vol 63 (3) ◽

Cited By ~ 18

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.

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In Vivo Fitness Adaptations of Colistin-Resistant Acinetobacter baumannii Isolates to Oxidative Stress

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00598-16 ◽

2016 ◽

Vol 61 (3) ◽

Cited By ~ 8

Author(s):

Crystal L. Jones ◽

Shweta S. Singh ◽

Yonas Alamneh ◽

Leila G. Casella ◽

Robert K. Ernst ◽

...

Keyword(s):

Oxidative Stress ◽

Hydrogen Peroxide ◽

Acinetobacter Baumannii ◽

Catalase Activity ◽

Content Type ◽

Increased Susceptibility

ABSTRACT The loss of fitness in colistin-resistant (CR) Acinetobacter baumannii was investigated using longitudinal isolates from the same patient. Early CR isolates were outcompeted by late CR isolates for growth in broth and survival in the lungs of mice. Fitness loss was associated with an increased susceptibility to oxidative stress since early CR strains had reduced in vitro survival in the presence of hydrogen peroxide and decreased catalase activity compared to that of late CR and colistin-susceptible (CS) strains.

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Role of Acinetobactin-Mediated Iron Acquisition Functions in the Interaction of Acinetobacter baumannii Strain ATCC 19606Twith Human Lung Epithelial Cells, Galleria mellonella Caterpillars, and Mice

Infection and Immunity ◽

10.1128/iai.06279-11 ◽

2012 ◽

Vol 80 (3) ◽

pp. 1015-1024 ◽

Cited By ~ 126

Author(s):

Jennifer A. Gaddy ◽

Brock A. Arivett ◽

Michael J. McConnell ◽

Rafael López-Rojas ◽

Jerónimo Pachón ◽

...

Keyword(s):

Epithelial Cells ◽

Acinetobacter Baumannii ◽

Galleria Mellonella ◽

Ex Vivo ◽

Iron Acquisition ◽

Alveolar Epithelial Cells ◽

Lung Epithelial Cells ◽

Content Type ◽

Alveolar Epithelial

Acinetobacter baumannii, which causes serious infections in immunocompromised patients, expresses high-affinity iron acquisition functions needed for growth under iron-limiting laboratory conditions. In this study, we determined that the initial interaction of the ATCC 19606Ttype strain with A549 human alveolar epithelial cells is independent of the production of BasD and BauA, proteins needed for acinetobactin biosynthesis and transport, respectively. In contrast, these proteins are required for this strain to persist within epithelial cells and cause their apoptotic death. Infection assays usingGalleria mellonellalarvae showed that impairment of acinetobactin biosynthesis and transport functions significantly reduces the ability of ATCC 19606Tcells to persist and kill this host, a defect that was corrected by adding inorganic iron to the inocula. The results obtained with theseex vivoandin vivoapproaches were validated using a mouse sepsis model, which showed that expression of the acinetobactin-mediated iron acquisition system is critical for ATCC 19606Tto establish an infection and kill this vertebrate host. These observations demonstrate that the virulence of the ATCC 19606Tstrain depends on the expression of a fully active acinetobactin-mediated system. Interestingly, the three models also showed that impairment of BasD production results in an intermediate virulence phenotype compared to those of the parental strain and the BauA mutant. This observation suggests that acinetobactin intermediates or precursors play a virulence role, although their contribution to iron acquisition is less relevant than that of mature acinetobactin.

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Phylogenomics of two ST1 antibiotic-susceptible non-clinical Acinetobacter baumannii strains reveals multiple lineages and complex evolutionary history in global clone 1

Microbial Genomics ◽

10.1099/mgen.0.000705 ◽

2021 ◽

Vol 7 (12) ◽

Author(s):

Jonathan Koong ◽

Claire Johnson ◽

Rayane Rafei ◽

Monzer Hamze ◽

Garry S. A. Myers ◽

...

Keyword(s):

Acinetobacter Baumannii ◽

Genome Sequence ◽

Evolutionary History ◽

Sequence Data ◽

Opportunistic Pathogen ◽

Outer Core ◽

Content Type ◽

Geographical Regions ◽

Long Read ◽

Complex Evolutionary History

Acinetobacter baumannii is an opportunistic pathogen that is difficult to treat due to its resistance to extreme conditions, including desiccation and antibiotics. Most strains causing outbreaks around the world belong to two main global lineages, namely global clones 1 and 2 (GC1 and GC2). Here, we used a combination of Illumina short read and MinION (Oxford Nanopore) long-read sequence data with a hybrid assembly approach to complete the genome sequence of two antibiotic-sensitive GC1 strains, Ex003 and Ax270, recovered in Lebanon from water and a rectal swab of a cat, respectively. Phylogenetic analysis of Ax270 and Ex003 with 186 publicly available GC1 genomes revealed two major clades, including five main lineages (L1–L5), and four single-isolate lineages outside of the two clades. Ax270 and Ex003, along with AB307-0294 and MRSN7213 (both predicted antibiotic-susceptible isolates) represent these individual lineages. Antibiotic resistance islands and transposons interrupting the comM gene remain important features in L1–L5, with L1 associated with the AbaR-type resistance islands, L2 with AbaR4, L3 strains containing either AbaR4 or its variants as well as Tn6022::ISAba42, and L4 and L5 associated with Tn6022 or its variants. Analysis of the capsule (KL) and outer core (OCL) polysaccharide loci further revealed a complex evolutionary history probably involving many recombination events. As more genomes become available, more GC1 lineages continue to emerge. However, genome sequence data from more diverse geographical regions are needed to draw a more accurate population structure of this globally distributed clone.

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