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

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

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01514-17 ◽

2017 ◽

Vol 62 (1) ◽

Cited By ~ 7

Author(s):

P. Malaka De Silva ◽

Patrick Chong ◽

Dinesh M. Fernando ◽

Garrett Westmacott ◽

Ayush Kumar

Keyword(s):

Acinetobacter Baumannii ◽

Galleria Mellonella ◽

Incubation Temperature ◽

Opportunistic Pathogen ◽

Effect Of Temperature ◽

Content Type ◽

Content Model ◽

Key Factor ◽

Plastic Surfaces ◽

Increased Susceptibility

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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Clinical and Epidemiological Significance of Carbapenem Resistance in Acinetobacter baumannii Infections

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02656-15 ◽

2016 ◽

Vol 60 (5) ◽

pp. 3127-3131 ◽

Cited By ~ 17

Author(s):

Ruthy Tal-Jasper ◽

David E. Katz ◽

Nadav Amrami ◽

Dor Ravid ◽

Dori Avivi ◽

...

Keyword(s):

Acinetobacter Baumannii ◽

Patient Outcomes ◽

Preventive Measures ◽

Carbapenem Resistance ◽

Content Type ◽

Carbapenem Resistant ◽

Multivariable Analyses ◽

Poor Outcomes ◽

Epidemiological Significance

ABSTRACTCarbapenems are considered the treatment of choice forAcinetobacter baumanniiinfections. Many facilities implement preventive measures toward only carbapenem-resistantA. baumannii(CRAB). However, the independent role of the carbapenem resistance determinant on patient outcomes remains controversial. In a 6-year analysis of adults withA. baumanniibloodstream infection (BSI), the outcomes of 149 CRAB isolates were compared to those of 91 patients with carbapenem-susceptibleA. baumannii. In bivariable analyses, CRAB BSIs were significantly associated with worse outcomes and with a delay in the initiation of appropriate antimicrobial therapy (DAAT). However, in multivariable analyses, carbapenem resistance status was no longer associated with poor outcomes, while DAAT remained an independent predictor. The epidemiological significance ofA. baumanniishould not be determined by its resistance to carbapenems.

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First Description of Two Sequence Type 2 Acinetobacter baumannii Isolates Carrying OXA-23 Carbapenemase in Pagellus acarne Fished from the Mediterranean Sea near Bejaia, Algeria

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02384-15 ◽

2016 ◽

Vol 60 (4) ◽

pp. 2513-2515 ◽

Cited By ~ 16

Author(s):

Soumia Brahmi ◽

Abdelaziz Touati ◽

Axelle Cadière ◽

Nassima Djahmi ◽

Alix Pantel ◽

...

Keyword(s):

Acinetobacter Baumannii ◽

Mediterranean Sea ◽

Sequence Type ◽

Content Type ◽

Carbapenem Resistant ◽

Selective Agar ◽

Agar Media ◽

The Mediterranean ◽

First Time

ABSTRACTTo determine the occurrence of carbapenem-resistantAcinetobacter baumanniiin fish fished from the Mediterranean Sea near the Bejaia coast (Algeria), we studied 300 gills and gut samples that had been randomly and prospectively collected during 1 year. After screening on selective agar media, using PCR arrays and whole-genome sequencing, we identified for the first time two OXA-23-producingA. baumanniistrains belonging to the widespread sequence type 2 (ST2)/international clone II and harboring aminoglycoside-modifying enzymes [aac(6′)-Ib andaac(3′)-I genes].

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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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Semimechanistic Pharmacokinetic/Pharmacodynamic Modeling of Fosfomycin and Sulbactam Combination against Carbapenem-Resistant Acinetobacter baumannii

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02472-20 ◽

2021 ◽

Vol 65 (5) ◽

Author(s):

Sazlyna Mohd Sazlly Lim ◽

Aaron J. Heffernan ◽

Jason A. Roberts ◽

Fekade B. Sime

Keyword(s):

Acinetobacter Baumannii ◽

Treatment Options ◽

Pharmacodynamic Modeling ◽

Synergistic Activity ◽

Bacterial Burden ◽

Target Attainment ◽

Content Type ◽

Carbapenem Resistant ◽

Time Kill

ABSTRACT Due to limited treatment options for carbapenem-resistant Acinetobacter baumannii (CR-AB) infections, antibiotic combinations are now considered potential treatments for CR-AB. This study aimed to explore the utility of fosfomycin-sulbactam combination (FOS/SUL) therapy against CR-AB isolates. Synergism of FOS/SUL against 50 clinical CR-AB isolates was screened using the checkerboard method. Thereafter, time-kill studies against two CR-AB isolates were performed. The time-kill data were described using a semimechanistic pharmacokinetic/pharmacodynamic (PK/PD) model. Monte Carlo simulations were then performed to estimate the probability of stasis, 1-log kill, and 2-log kill after 24 h of combination therapy. The FOS/SUL combination demonstrated a synergistic effect against 74% of isolates. No antagonism was observed. The MIC50 and MIC90 of FOS/SUL were decreased 4- to 8-fold, compared to the monotherapy MIC50 and MIC90. In the time-kill studies, the combination displayed bactericidal activity against both isolates and synergistic activity against one isolate at the highest clinically achievable concentrations. Our PK/PD model was able to describe the interaction between fosfomycin and sulbactam in vitro. Bacterial kill was mainly driven by sulbactam, with fosfomycin augmentation. FOS/SUL regimens that included sulbactam at 4 g every 8 h demonstrated a probability of target attainment of 1-log10 kill at 24 h of ∼69 to 76%, compared to ∼15 to 30% with monotherapy regimens at the highest doses. The reduction in the MIC values and the achievement of a moderate PTA of a 2-log10 reduction in bacterial burden demonstrated that FOS/SUL may potentially be effective against some CR-AB infections.

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Mutations in the two component regulator systems PmrAB and PhoPQ give rise to increased colistin resistance in Citrobacter and Enterobacter spp.

Journal of Medical Microbiology ◽

10.1099/jmm.0.001173 ◽

2020 ◽

Vol 69 (4) ◽

pp. 521-529 ◽

Cited By ~ 1

Author(s):

Matthew E. Wand ◽

J. Mark Sutton

Keyword(s):

Growth Rate ◽

Type Species ◽

Galleria Mellonella ◽

Strain Differences ◽

Fold Increase ◽

Colistin Resistance ◽

Content Type ◽

Link Type ◽

Carbapenem Resistant ◽

Individual Strain

Introduction. Colistin is a last resort antibiotic for treating infections caused by carbapenem-resistant isolates. Mechanisms of resistance to colistin have been widely described in Klebsiella pneumoniae and Escherichia coli but have yet to be characterized in Citrobacter and Enterobacter species. Aim. To identify the causative mutations leading to generation of colistin resistance in Citrobacter and Enterobacter spp. Methodology. Colistin resistance was generated by culturing in increasing concentrations of colistin or by direct culture in a lethal (above MIC) concentration. Whole-genome sequencing was used to identify mutations. Fitness of resistant strains was determined by changes in growth rate, and virulence in Galleria mellonella. Results. We were able to generate colistin resistance upon exposure to sub-MIC levels of colistin, in several but not all strains of Citrobacter and Enterobacter resulting in a 16-fold increase in colistin MIC values for both species. The same individual strains also developed resistance to colistin after a single exposure at 10× MIC, with a similar increase in MIC. Genetic analysis revealed that this increased resistance was attributed to mutations in PmrB for Citrobacter and PhoP in Enterobacter , although we were not able to identify causative mutations in all strains. Colistin-resistant mutants showed little difference in growth rate, and virulence in G. mellonella, although there were strain-to-strain differences. Conclusions. Stable colistin resistance may be acquired with no loss of fitness in these species. However, only select strains were able to adapt suggesting that acquisition of colistin resistance is dependent upon individual strain characteristics.

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Combating Carbapenem-ResistantAcinetobacter baumanniiby an Optimized Imipenem-plus-Tobramycin Dosage Regimen: Prospective Validation via Hollow-Fiber Infection and Mathematical Modeling

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02053-17 ◽

2018 ◽

Vol 62 (4) ◽

Cited By ~ 7

Author(s):

Cornelia B. Landersdorfer ◽

Rajbharan Yadav ◽

Kate E. Rogers ◽

Tae Hwan Kim ◽

Beom Soo Shin ◽

...

Keyword(s):

Mathematical Modeling ◽

Acinetobacter Baumannii ◽

Hollow Fiber ◽

Dosage Regimen ◽

Infection Model ◽

Bacterial Killing ◽

Content Type ◽

Carbapenem Resistant

ABSTRACTWe aimed to prospectively validate an optimized combination dosage regimen against a clinical carbapenem-resistantAcinetobacter baumannii(CRAB) isolate (imipenem MIC, 32 mg/liter; tobramycin MIC, 2 mg/liter). Imipenem at constant concentrations (7.6, 13.4, and 23.3 mg/liter, reflecting a range of clearances) was simulated in a 7-day hollow-fiber infection model (inoculum, ∼107.2CFU/ml) with and without tobramycin (7 mg/kg q24h, 0.5-h infusions). While monotherapies achieved no killing or failed by 24 h, this rationally optimized combination achieved >5 log10bacterial killing and suppressed resistance.

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Draft Genome Sequences of Two Acinetobacter baumannii Isolates from a Fatal Case of Necrotizing Fasciitis

Microbiology Resource Announcements ◽

10.1128/mra.00047-20 ◽

2020 ◽

Vol 9 (13) ◽

Author(s):

Brock A. Arivett ◽

Angella Charnot-Katsikas ◽

Cindy Bethel ◽

Steven E. Fiester ◽

Luis A. Actis

Keyword(s):

Necrotizing Fasciitis ◽

Acinetobacter Baumannii ◽

Fatal Case ◽

Draft Genome ◽

Bacterial Pathogen ◽

Genome Sequences ◽

Content Type ◽

Carbapenem Resistant ◽

Control And Prevention ◽

Total Dna

Carbapenem-resistant Acinetobacter baumannii is a bacterial pathogen with serious implications for human health and is recognized as an urgent threat by the Centers for Disease Control and Prevention (CDC). Total DNA from two A. baumannii clinical isolates collected over 3 days from a fatal case of necrotizing fasciitis has been sequenced to >30× coverage.

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Accumulation of Antibiotic Resistance Genes in Carbapenem-Resistant Acinetobacter baumannii Isolates Belonging to Lineage 2, Global Clone 1, from Outbreaks in 2012–2013 at a Tehran Burns Hospital

mSphere ◽

10.1128/msphere.00164-20 ◽

2020 ◽

Vol 5 (2) ◽

Cited By ~ 2

Author(s):

Masoumeh Douraghi ◽

Johanna J. Kenyon ◽

Parisa Aris ◽

Mahla Asadian ◽

Sedighe Ghourchian ◽

...

Keyword(s):

Middle East ◽

Acinetobacter Baumannii ◽

Resistance Genes ◽

Carbapenem Resistance ◽

Antibiotic Resistant ◽

Content Type ◽

Carbapenem Resistant ◽

East Region ◽

Lineage 2 ◽

Middle East Region

ABSTRACT The worldwide distribution of carbapenem-resistant Acinetobacter baumannii (CRAB) has become a global concern, particularly in countries where antibiotic prescription is not tightly regulated. However, knowledge of the genomic aspects of CRAB from many parts of the world is still limited. Here, 50 carbapenem-resistant A. baumannii isolates recovered at a single hospital in Tehran, Iran, during several outbreaks in 2012 and 2013 were found to be resistant to multiple antibiotics. They were examined using PCR mapping and multilocus sequence typing (MLST). All Iranian strains belonged to sequence type 328 in the Institut Pasteur MLST scheme (ST328IP), a single-locus variant of ST81IP, and all Iranian strains contained two carbapenem resistance genes, oxa23 and oxa24. The oxa23 gene is in the transposon Tn2006 in AbaR4, which interrupts the chromosomal comM gene. Phylogenetic analysis using whole-genome sequence (WGS) data for 9 isolates showed that they belonged to the same clade, designated the ST81/ST328 clade, within lineage 2 of global clone 1 (GC1). However, there were two groups that included either KL13 or KL18 at the K locus (KL) for capsular polysaccharide synthesis and either a tet39 or an aadB resistance gene, respectively. The genetic context of the resistance genes was determined, and the oxa24 (OXA-72 variant) and tet39 (tetracycline resistance) genes were each in a pdif module in different plasmids. The aadB gene cassette (which encodes gentamicin, kanamycin, and tobramycin resistance) was harbored by pRAY*, and the aphA6 gene (which encodes amikacin resistance) and sul2 gene (which encodes sulfamethoxazole resistance) were each harbored by a different plasmid. The sequences obtained here will underpin future studies of GC1 CRAB strains from the Middle East region. IMPORTANCE Carbapenem-resistant Acinetobacter baumannii strains are among the most critical antibiotic-resistant bacteria causing hospital-acquired infections and treatment failures. The global spread of two clones has been responsible for the bulk of the resistance, in particular, carbapenem resistance. However, there is a substantial gap in our knowledge of which clones and which specific lineages within each clone are circulating in many parts of the world, including Africa and the Middle East region. This is the first genomic analysis of carbapenem-resistant A. baumannii strains from Iran. All the isolates, from a single hospital, belonged to lineage 2 of global clone 1 (GC1) but fell into two groups distinguished by genes in the locus for capsule biosynthesis. The analysis suggests a potential origin of multiply antibiotic-resistant lineage 2 in the Middle East region and highlights the ongoing evolution of carbapenem-resistant GC1 A. baumannii strains. It will enhance future studies on the local and global GC1 population structure.

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