scholarly journals Peptidoglycan recycling contributes to outer membrane integrity and carbapenem tolerance in Acinetobacter baumannii

2021 ◽  
Author(s):  
Nowrosh Islam ◽  
Misha I. Kazi ◽  
Katie N. Kang ◽  
Jacob Biboy ◽  
Joe Gray ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Outer Membrane ◽  
Cell Envelope ◽  
Membrane Integrity ◽  
Normal Growth ◽  
Multidrug Resistant ◽  
Antibiotic Tolerance ◽  
Gram Negative ◽  
Tolerance Factors ◽  
The Impact

The Gram-negative cell envelope is an essential structure that not only protects the cell against lysis from the internal turgor, but also forms a barrier to limit entry of antibiotics. Some of our most potent bactericidal antibiotics, the β-lactams, exploit the essentiality of the cell envelope by inhibiting its biosynthesis, typically inducing lysis and rapid death. However, many Gram-negative bacteria exhibit antibiotic tolerance, the ability to sustain viability in the presence of β-lactams for extended time periods. Despite several studies showing that antibiotic tolerance contributes directly to treatment failure, and is a steppingstone in acquisition of true resistance, the molecular factors that promote intrinsic tolerance are not well-understood. Acinetobacter baumannii is a critical-threat nosocomial pathogen notorious for its ability to rapidly develop multidrug resistance. While typically reserved to combat multidrug resistant infections, carbapenem β-lactam antibiotics (i.e., meropenem) are first-line prescriptions to treat A. baumannii infections. Meropenem tolerance in Gram-negative pathogens is characterized by morphologically distinct populations of spheroplasts, but the impact of spheroplast formation is not fully understood. Here, we show that susceptible A. baumannii clinical isolates demonstrate high intrinsic tolerance to meropenem, form spheroplasts with the antibiotic and revert to normal growth after antibiotic removal. Using transcriptomics and genetics screens, we characterized novel tolerance factors and found that outer membrane integrity maintenance, drug efflux and peptidoglycan homeostasis collectively contribute to meropenem tolerance in A. baumannii. Furthermore, outer membrane integrity and peptidoglycan recycling are tightly linked in their contribution to meropenem tolerance in A. baumannii.

scholarly journals Acinetobacter baumannii Can Survive with an Outer Membrane Lacking Lipooligosaccharide Due to Structural Support from Elongasome Peptidoglycan Synthesis

mBio ◽  
2021 ◽  
Author(s):  
Brent W. Simpson ◽  
Marta Nieckarz ◽  
Victor Pinedo ◽  
Amanda B. McLean ◽  
Felipe Cava ◽  
...  
Keyword(s):  
Mechanical Strength ◽  
Acinetobacter Baumannii ◽  
Outer Membrane ◽  
Cell Envelope ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Structural Support ◽  
Peptidoglycan Synthesis

Gram-negative bacteria have a multilayered cell envelope with a layer of cross-linked polymers (peptidoglycan) sandwiched between two membranes. Peptidoglycan was long thought to exclusively provide rigidity to the cell providing mechanical strength.

scholarly journals Epidemiology of Multidrug-resistant Bacteria Isolated from Hospitalized Patients in a Regional Central Hospital in China

2020 ◽  
Author(s):  
Jixun Zhang ◽  
Rui Li ◽  
Zhenzhong Liu ◽  
Chao Wang
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Acinetobacter Baumannii ◽  
Multidrug Resistant ◽  
Hospitalized Patients ◽  
Resistant Bacteria ◽  
Central Hospital ◽  
Gram Negative ◽  
E Coli ◽  
Significant Difference ◽  
The Impact

Abstract Objectives: Considering the dynamic changes of MDR, we did an up-to-date study and analyzed the impact of MDR on the outcome of patients. Design: Collected MDR isolated from hospitalized patients between June 2018 and May 2020 and performed retrospective analysis. Setting: This study was conducted in a public regional central hospital in China.Patients: 1156 patients with MDR infections.Results: Total 1291 MDRS were isolated, intensive care unit (ICU) accounted for 32.3% as the most. The main samples were sputum (75.1%) and 89.6% MDR were Gram-negative. The most common MDR were Acinetobacter baumannii, carbapenemase-producing K. pneumoniae, Pseudomonas aeruginosa, ESBL-producing E. coli. Methicillin-resistant Staphylococcus aureus (MRSA) and ESBL-producing K.pneumoniae. 35.6% were nosocomial infections and 64.4% were community-acquired infections. There was a statistically significant difference in mortality between patients infected with MDR and those with non-MDR (7.4% [32/432] vs 2.6% [17/655]; P = 0.001). The Acinetobacter baumannii and Klebsiella pneumoniae were mainly sensitive to tigecycline. The Pseudomonas aeruginosa was mainly sensitive to amikacin and levofloxacin. More than 80% of the Escherichia coli were sensitive to tigecycline and carbapenems. More than 90% of MRSA were sensitive to vancomycin, linezolid, and quinoprptin / daptoptin.Conclusions: The MDRS are mainly gram-negative bacteria. ICU contributes most MDR and pulmonary infection is the main origin of MDR. MDR infection is an independent risk factor for death. ESBL-producing Enterobacteriaceae, especially carbapenemase producing Enterobacteriaceae, should be paid more attention. This study is helpful to understand the distribution of MDR in hospital and the extent of antibiotic resistance.

scholarly journals Donnan Potential across the Outer Membrane of Gram-Negative Bacteria and Its Effect on the Permeability of Antibiotics

Antibiotics ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 701
Author(s):  
Olaniyi Alegun ◽  
Ankit Pandeya ◽  
Jian Cui ◽  
Isoiza Ojo ◽  
Yinan Wei
Keyword(s):  
Outer Membrane ◽  
Cell Envelope ◽  
Gram Negative Bacteria ◽  
Donnan Potential ◽  
Periplasmic Space ◽  
Lipid Bilayer Membranes ◽  
Surface Charges ◽  
Gram Negative ◽  
Selective Permeability ◽  
The Impact

The cell envelope structure of Gram-negative bacteria is unique, composed of two lipid bilayer membranes and an aqueous periplasmic space sandwiched in between. The outer membrane constitutes an extra barrier to limit the exchange of molecules between the cells and the exterior environment. Donnan potential is a membrane potential across the outer membrane, resulted from the selective permeability of the membrane, which plays a pivotal role in the permeability of many antibiotics. In this review, we discussed factors that affect the intensity of the Donnan potential, including the osmotic strength and pH of the external media, the osmoregulated periplasmic glucans trapped in the periplasmic space, and the displacement of cell surface charges. The focus of our discussion is the impact of Donnan potential on the cellular permeability of selected antibiotics including fluoroquinolones, tetracyclines, β-lactams, and trimethoprim.

scholarly journals Emergence of a Competence-Reducing Filamentous Phage from the Genome of Acinetobacter baylyi ADP1

2016 ◽  
Vol 198 (23) ◽  
pp. 3209-3219 ◽  
Author(s):  
Brian A. Renda ◽  
Cindy Chan ◽  
Kristin N. Parent ◽  
Jeffrey E. Barrick
Keyword(s):  
Acinetobacter Baumannii ◽  
Vibrio Cholerae ◽  
Bacterial Species ◽  
Normal Growth ◽  
Multidrug Resistant ◽  
Filamentous Phage ◽  
Acinetobacter Baylyi ◽  
Laboratory Evolution ◽  
Content Type ◽  
Evolution Experiment

ABSTRACTBacterial genomes commonly contain prophage sequences as a result of past infections with lysogenic phages. Many of these integrated viral sequences are believed to be cryptic, but prophage genes are sometimes coopted by the host, and some prophages may be reactivated to form infectious particles when cells are stressed or mutate. We found that a previously uncharacterized filamentous phage emerged from the genome ofAcinetobacter baylyiADP1 during a laboratory evolution experiment. This phage has a genetic organization similar to that of theVibrio choleraeCTXϕ phage. The emergence of the ADP1 phage was associated with the evolution of reduced transformability in our experimental populations, so we named it thecompetence-reducingacinetobacter phage (CRAϕ). Knocking out ADP1 genes required for competence leads to resistance to CRAϕ infection. Although filamentous bacteriophages are known to target type IV pili, this is the first report of a phage that apparently uses a competence pilus as a receptor.A. baylyimay be especially susceptible to this route of infection because every cell is competent during normal growth, whereas competence is induced only under certain environmental conditions or in a subpopulation of cells in other bacterial species. It is possible that CRAϕ-like phages restrict horizontal gene transfer in nature by inhibiting the growth of naturally transformable strains. We also found that prophages with homology to CRAϕ exist in several strains ofAcinetobacter baumannii. These CRAϕ-likeA. baumanniiprophages encode toxins similar to CTXϕ that might contribute to the virulence of this opportunistic multidrug-resistant pathogen.IMPORTANCEWe observed the emergence of a novel filamentous phage (CRAϕ) from the genome ofAcinetobacter baylyiADP1 during a long-term laboratory evolution experiment. CRAϕ is the first bacteriophage reported to require the molecular machinery involved in the uptake of environmental DNA for infection. Reactivation and evolution of CRAϕ reduced the potential for horizontal transfer of genes via natural transformation in our experiment. Risk of infection by similar phages may limit the expression and maintenance of bacterial competence in nature. The closest studied relative of CRAϕ is theVibrio choleraeCTXϕ phage. Variants of CRAϕ are found in the genomes ofAcinetobacter baumanniistrains, and it is possible that phage-encoded toxins contribute to the virulence of this opportunistic multidrug-resistant pathogen.

scholarly journals In VitroActivity of RX-P873 against Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii

2015 ◽  
Vol 59 (4) ◽  
pp. 2280-2285 ◽  
Author(s):  
Robert K. Flamm ◽  
Paul R. Rhomberg ◽  
Ronald N. Jones ◽  
David J. Farrell
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Acinetobacter Baumannii ◽  
Active Agent ◽  
Multidrug Resistant ◽  
Surveillance Program ◽  
Gram Negative ◽  
Content Type ◽  
Highly Active ◽  
Bacterial Ribosome

ABSTRACTRX-P873 is a novel antibiotic from the pyrrolocytosine series which exhibits high binding affinity for the bacterial ribosome and broad-spectrum antibiotic properties. The pyrrolocytosines have shownin vitroactivity against multidrug-resistant Gram-negative and Gram-positive strains of bacteria known to cause complicated urinary tract, skin, and lung infections, as well as sepsis.Enterobacteriaceae(657),Pseudomonas aeruginosa(200), andAcinetobacter baumannii(202) isolates from North America and Europe collected in 2012 as part of a worldwide surveillance program were testedin vitroby broth microdilution using Clinical and Laboratory Standards Institute (CLSI) methodology. RX-P873 (MIC90, 0.5 μg/ml) was >32-fold more active than ceftazidime and inhibited 97.1% and 99.5% ofEnterobacteriaceaeisolates at MIC values of ≤1 and ≤4 μg/ml, respectively. There were only three isolates with an MIC value of >4 μg/ml (all were indole-positiveProtea). RX-P873 (MIC50/90, 2/4 μg/ml) was highly active againstPseudomonas aeruginosaisolates, including isolates which were nonsusceptible to ceftazidime or meropenem. RX-P873 was 2-fold less active againstP. aeruginosathan tobramycin (MIC90, 2 μg/ml; 91.0% susceptible) and colistin (MIC90, 2 μg/ml; 99.5% susceptible) and 2-fold more potent than amikacin (MIC90, 8 μg/ml; 93.5% susceptible) and meropenem (MIC90, 8 μg/ml; 76.0% susceptible). RX-P873, the most active agent againstAcinetobacter baumannii(MIC90, 1 μg/ml), was 2-fold more active than colistin (MIC90, 2 μg/ml; 97.0% susceptible) and 4-fold more active than tigecycline (MIC90, 4 μg/ml). This novel agent merits further exploration of its potential against multidrug-resistant Gram-negative bacteria.

Genomic fitness profiling of Acinetobacter baumannii reveals modes of action for common biocides and mechanisms of biocide-antibiotic antagonism

2021 ◽  
Author(s):  
Liping Li ◽  
Francesca Short ◽  
Karl Hassan ◽  
Varsha Naidu ◽  
Alaska Pokhrel ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Pathogenic Bacteria ◽  
Cell Envelope ◽  
Tricarboxylic Acid Cycle ◽  
Insertion Site ◽  
Multidrug Resistant ◽  
Resistant Bacteria ◽  
Cell Respiration ◽  
Community Environments ◽  
Intracellular Targets

Abstract Biocides, such as antiseptics and disinfectants, are used ubiquitously for hygiene in households and for life-saving infection control in hospitals. An increasing concern is that the widespread use of biocides may contribute to the emergence and spread of multidrug-resistant bacteria. We performed transposon directed insertion site sequencing (TraDIS) to identify genes and key cellular pathways of the multidrug resistant nosocomial pathogen Acinetobacter baumannii, that affect host fitness during exposure to a panel of ten structurally-diverse and clinically-relevant biocides: silver nitrate, benzalkonium, cetyltrimethylammonium bromide (CTAB), chlorhexidine, triclosan, chloroxylenol, polyvidone iodine, bleach, glutaraldehyde and ethanol. Multiple genes encoding proteins localised either in the cell envelope or in the cytoplasm were shown to affect biocide susceptibility. These proteins are involved in multiple processes including fatty acid biogenesis, multidrug efflux, the tricarboxylic acid cycle, cell respiration and cell division, suggesting that these biocides may have intracellular targets in addition to their known effects on the cell envelope. Based on the importance of cell respiration genes for A. baumannii fitness on biocides, we proposed and confirmed that apart from triclosan, the other 9 biocides at sub-inhibitory concentration can dissipate the membrane potential and lead to A. baumannii tolerance to antibiotics that have intracellular targets. Our results support the concern that residual biocides in clinical or community environments can promote the development of antibiotic resistance in pathogenic bacteria.

scholarly journals Robust Suppression of Lipopolysaccharide Deficiency in Acinetobacter baumannii by Growth in Minimal Medium

2019 ◽  
Vol 201 (22) ◽  
Author(s):  
Emma Nagy ◽  
Richard Losick ◽  
Daniel Kahne
Keyword(s):  
Acinetobacter Baumannii ◽  
Outer Membrane ◽  
Minimal Medium ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Content Type ◽  
Growth Defects ◽  
Outer Leaflet ◽  
Morphological Defects ◽  
Outer Membrane Biogenesis

ABSTRACT Lipopolysaccharide (LPS) is normally considered to be essential for viability in Gram-negative bacteria but can be removed in Acinetobacter baumannii. Mutant cells lacking this component of the outer membrane show growth and morphological defects. Here, we report that growth rates equivalent to the wild type can be achieved simply by propagation in minimal medium. The loss of LPS requires that cells rely on phospholipids for both leaflets of the outer membrane. We show that growth rate in the absence of LPS is not limited by nutrient availability but by the rate of outer membrane biogenesis. We hypothesize that because cells grow more slowly, outer membrane synthesis ceases to be rate limiting in minimal medium. IMPORTANCE Gram-negative bacteria are defined by their asymmetric outer membrane that consists of phospholipids on the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. LPS is essential in all but a few Gram-negative species; the reason for this differential essentiality is not well understood. One species that can survive without LPS, Acinetobacter baumannii, shows characteristic growth and morphology phenotypes. We show that these phenotypes can be suppressed under conditions of slow growth and describe how LPS loss is connected to the growth defects. In addition to better defining the challenges A. baumannii cells face in the absence of LPS, we provide a new hypothesis that may explain the species-dependent conditional essentiality.

scholarly journals A small-molecule inhibitor of BamA impervious to efflux and the outer membrane permeability barrier

2019 ◽  
Vol 116 (43) ◽  
pp. 21748-21757 ◽  
Author(s):  
Elizabeth M. Hart ◽  
Angela M. Mitchell ◽  
Anna Konovalova ◽  
Marcin Grabowicz ◽  
Jessica Sheng ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Small Molecule ◽  
Cytoplasmic Membrane ◽  
Multidrug Resistant ◽  
Resistant Bacteria ◽  
Permeability Barrier ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Bam Complex ◽  
Induced Aggregation

The development of new antimicrobial drugs is a priority to combat the increasing spread of multidrug-resistant bacteria. This development is especially problematic in gram-negative bacteria due to the outer membrane (OM) permeability barrier and multidrug efflux pumps. Therefore, we screened for compounds that target essential, nonredundant, surface-exposed processes in gram-negative bacteria. We identified a compound, MRL-494, that inhibits assembly of OM proteins (OMPs) by the β-barrel assembly machine (BAM complex). The BAM complex contains one essential surface-exposed protein, BamA. We constructed a bamA mutagenesis library, screened for resistance to MRL-494, and identified the mutation bamAE470K. BamAE470K restores OMP biogenesis in the presence of MRL-494. The mutant protein has both altered conformation and activity, suggesting it could either inhibit MRL-494 binding or allow BamA to function in the presence of MRL-494. By cellular thermal shift assay (CETSA), we determined that MRL-494 stabilizes BamA and BamAE470K from thermally induced aggregation, indicating direct or proximal binding to both BamA and BamAE470K. Thus, it is the altered activity of BamAE470K responsible for resistance to MRL-494. Strikingly, MRL-494 possesses a second mechanism of action that kills gram-positive organisms. In microbes lacking an OM, MRL-494 lethally disrupts the cytoplasmic membrane. We suggest that the compound cannot disrupt the cytoplasmic membrane of gram-negative bacteria because it cannot penetrate the OM. Instead, MRL-494 inhibits OMP biogenesis from outside the OM by targeting BamA. The identification of a small molecule that inhibits OMP biogenesis at the cell surface represents a distinct class of antibacterial agents.

scholarly journals Outer Membrane Interaction Kinetics of New Polymyxin B Analogs in Gram-Negative Bacilli

2019 ◽  
Vol 63 (10) ◽  
Author(s):  
Noushin Akhoundsadegh ◽  
Corrie R. Belanger ◽  
Robert E. W. Hancock
Keyword(s):  
Outer Membrane ◽  
Polymyxin B ◽  
Multidrug Resistant ◽  
Intact Cells ◽  
Membrane Interaction ◽  
Gram Negative ◽  
Content Type ◽  
Interaction Kinetics ◽  
Hill Numbers ◽  
Multiple Strains

ABSTRACT Infections caused by drug-resistant Gram-negative bacilli are a severe global health threat, limiting effective drug choices for treatment. In this study, polymyxin analogs designed to have reduced nephrotoxicity, direct activity, and potentiating activity were assessed for inhibition and outer membrane interaction kinetics against wild-type (WT) and polymyxin or multidrug-resistant (MDR) Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. In MIC assays, two polymyxin B (PMB) analogs (SPR1205 and SPR206) and a polymyxin E analog (SPR946), with shortened peptide side chains and branched aminobutyryl N termini, exhibited promising activity compared with PMB and previously tested control polymyxin analogs SPR741 and polymyxin B nonapeptide (PMBN). Using dansyl-polymyxin (DPX) binding to assess the affinity of interaction with lipopolysaccharide (LPS), purified or in the context of intact cells, SPR206 exhibited similar affinities to PMB but higher affinities than the other SPR analogs. Outer membrane permeabilization measured by the 1-N-phenyl-napthylamine (NPN) assay did not differ significantly between the polymyxin analogs. Moreover, Hill numbers were greater than 1 for most of the compounds tested on E. coli and P. aeruginosa strains which indicates that the disruption of the outer membrane by one molecule of compound cooperatively enhances the subsequent interactions of other molecules against WT and MDR strains. The high activity demonstrated by SPR206 as well as its ability to displace LPS and permeabilize the outer membrane of multiple strains of Gram-negative bacilli while showing cooperative potential with other membrane disrupting compounds supports further research with this polymyxin analog.

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