scholarly journals Unique Structural Modifications Are Present in the Lipopolysaccharide from Colistin-Resistant Strains of Acinetobacter baumannii

2013 ◽  
Vol 57 (10) ◽  
pp. 4831-4840 ◽  
Author(s):  
Mark R. Pelletier ◽  
Leila G. Casella ◽  
Jace W. Jones ◽  
Mark D. Adams ◽  
Daniel V. Zurawski ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Lipid A ◽  
Opportunistic Pathogen ◽  
Structure Characterization ◽  
Resistant Isolate ◽  
Patient Treatment ◽  
Cationic Antimicrobial Peptide ◽  
Content Type ◽  
Lipid A Structure ◽  
Resistant Strains

ABSTRACTAcinetobacter baumanniiis a nosocomial opportunistic pathogen that can cause severe infections, including hospital-acquired pneumonia, wound infections, and sepsis. Multidrug-resistant (MDR) strains are prevalent, further complicating patient treatment. Due to the increase in MDR strains, the cationic antimicrobial peptide colistin has been used to treatA. baumanniiinfections. Colistin-resistant strains ofA. baumanniiwith alterations to the lipid A component of lipopolysaccharide (LPS) have been reported; specifically, the lipid A structure was shown to be hepta-acylated with a phosphoethanolamine (pEtN) modification present on one of the terminal phosphate residues. Using a tandem mass spectrometry platform, we provide definitive evidence that the lipid A isolated from colistin-resistantA. baumanniiMAC204 LPS contains a novel structure corresponding to a diphosphoryl hepta-acylated lipid A structure with both pEtN and galactosamine (GalN) modifications. To correlate our structural studies with clinically relevant samples, we characterized colistin-susceptible and -resistant isolates obtained from patients. These results demonstrated that the clinical colistin-resistant isolate had the same pEtN and GalN modifications as those seen in the laboratory-adaptedA. baumanniistrain MAC204. In summary, this work has shown complete structure characterization including the accurate assignment of acylation, phosphorylation, and glycosylation of lipid A fromA. baumannii, which are important for resistance to colistin.

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 Reinforcing Lipid A Acylation on the Cell Surface of Acinetobacter baumannii Promotes Cationic Antimicrobial Peptide Resistance and Desiccation Survival

mBio ◽  
2015 ◽  
Vol 6 (3) ◽  
Author(s):  
Joseph M. Boll ◽  
Ashley T. Tucker ◽  
Dustin R. Klein ◽  
Alexander M. Beltran ◽  
Jennifer S. Brodbelt ◽  
...  
Keyword(s):  
Health Care ◽  
Acinetobacter Baumannii ◽  
Outer Membrane ◽  
Lipid A ◽  
Treatment Options ◽  
Cationic Antimicrobial Peptide ◽  
Gram Negative ◽  
Content Type ◽  
Hospital Environments ◽  
Lipid A Biosynthesis

ABSTRACTAcinetobacter baumanniiis an emerging Gram-negative pathogen found in hospitals and intensive care units. In order to persist in hospital environments,A. baumanniiwithstands desiccative conditions and can rapidly develop multidrug resistance to conventional antibiotics. Cationic antimicrobial peptides (CAMPs) have served as therapeutic alternatives because they target the conserved lipid A component of the Gram-negative outer membrane to lyse the bacterial cell. However, many Gram-negative pathogenic bacteria, includingA. baumannii, fortify their outer membrane with hepta-acylated lipid A to protect the cell from CAMP-dependent cell lysis. Whereas inEscherichia coliandSalmonella, increased production of the outer membrane acyltransferase PagP results in formation of protective hepta-acylated lipid A, which reinforces the lipopolysaccharide portion of the outer membrane barrier,A. baumanniidoes not carry a gene that encodes a PagP homolog. Instead,A. baumanniihas evolved a PagP-independent mechanism to synthesize protective hepta-acylated lipid A. Taking advantage of a recently adaptedA. baumanniigenetic recombineering system, we characterized two putative acyltransferases inA. baumanniidesignated LpxLAb(A. baumanniiLpxL) and LpxMAb(A. baumanniiLpxM), which transfer one and two lauroyl (C12:0) acyl chains, respectively, during lipid A biosynthesis. Hepta-acylation ofA. baumanniilipid A promoted resistance to vertebrate and polymyxin CAMPs, which are prescribed as last-resort treatment options. Intriguingly, our analysis also showed that LpxMAb-dependent acylation of lipid A is essential forA. baumanniidesiccation survival, a key resistance mechanism for survival in hospital environments. Compounds that inhibit LpxMAb-dependent hepta-acylation of lipid A could act synergistically with CAMPs to provide innovative transmission prevention strategies and treat multidrug-resistant infections.IMPORTANCEAcinetobacter baumanniiinfections can be life threatening, and disease can progress in a variety of host tissues. Current antibiotic regimen and disinfectant strategies have failed to limit nosocomialA. baumanniiinfections. Instead, the rate ofA. baumanniiinfection among health care communities has skyrocketed due to the bacterium's adaptability. Its aptitude for survival over extended periods on inanimate objects, such as catheters, respirators, and surfaces in intensive care units, or on the hands of health care workers and its ability to rapidly develop antibiotic resistance makeA. baumanniia threat to health care communities. Emergence of multidrug- and extremely drug-resistantA. baumanniiillustrates the ineffectiveness of current prevention and treatment options. Our analysis to understand howA. baumanniiresists cationic antimicrobial peptide (CAMP)-mediated and desiccative killing revealed two lipid A acyltransferases that produce protective hepta-acylated lipid A. Our work suggests that inhibiting lipid A biosynthesis by targeting the acyltransferase LpxMAb(A. baumanniiLpxM) could provide a novel target to combat this pathogen.

scholarly journals Synergy between Colistin and the Signal Peptidase Inhibitor MD3 Is Dependent on the Mechanism of Colistin Resistance in Acinetobacter baumannii

2016 ◽  
Vol 60 (7) ◽  
pp. 4375-4379 ◽  
Author(s):  
Marta Martínez-Guitián ◽  
Juan C. Vázquez-Ucha ◽  
Joshua Odingo ◽  
Tanya Parish ◽  
Margarita Poza ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Lipid A ◽  
Growth Curves ◽  
Resistance Mechanisms ◽  
Signal Peptidase ◽  
Colistin Resistance ◽  
Content Type ◽  
Peptidase Inhibitor ◽  
Resistant Strains ◽  
Isogenic Mutants

ABSTRACTSynergy between colistin and the signal peptidase inhibitor MD3 was tested against isogenic mutants and clinical pairs ofAcinetobacter baumanniiisolates. Checkerboard assays and growth curves showed synergy against both colistin-susceptible strains (fractional inhibitory concentration index [FICindex] = 0.13 to 0.24) and colistin-resistant strains with mutations inpmrBand phosphoethanolamine modification of lipid A (FICindex= 0.14 to 0.25) but not against colistin-resistant Δlpxstrains with loss of lipopolysaccharide (FICindex= 0.75 to 1). A colistin/MD3 combination would need to be targeted to strains with specific colistin resistance mechanisms.

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 Lon Protease Has Multifaceted Biological Functions inAcinetobacter baumannii

2018 ◽  
Vol 201 (2) ◽  
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.

scholarly journals A Prospective Study of Acinetobacter baumannii Complex Isolates and Colistin Susceptibility Monitoring by Mass Spectrometry of Microbial Membrane Glycolipids

2018 ◽  
Vol 57 (3) ◽  
Author(s):  
Lisa M. Leung ◽  
Christi L. McElheny ◽  
Francesca M. Gardner ◽  
Courtney E. Chandler ◽  
Sarah L. Bowler ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Acinetobacter Baumannii ◽  
Lipid A ◽  
Membrane Lipids ◽  
Clinical Isolates ◽  
Colistin Resistance ◽  
Hospital System ◽  
Content Type ◽  
Acinetobacter Baumannii Complex ◽  
Gram Negative Organisms

ABSTRACT Acinetobacter baumannii is a prevalent nosocomial pathogen with a high incidence of multidrug resistance. Treatment of infections due to this organism with colistin, a last-resort antibiotic of the polymyxin class, can result in the emergence of colistin-resistant strains. Colistin resistance primarily occurs via modifications of the terminal phosphate moieties of lipopolysaccharide-derived lipid A, which reduces overall membrane electronegativity. These modifications are readily identified by mass spectrometry (MS). In this study, we prospectively collected Acinetobacter baumannii complex clinical isolates from a hospital system in Pennsylvania over a 3-year period. All isolates were evaluated for colistin resistance using standard MIC testing by both agar dilution and broth microdilution, as well as genospecies identification and lipid A profiling using MS analyses. Overall, an excellent correlation between colistin susceptibility and resistance, determined by MIC testing, and the presence of a lipid A modification, determined by MS, was observed with a sensitivity of 92.9% and a specificity of 94.0%. Additionally, glycolipid profiling was able to differentiate A. baumannii complex organisms based on their membrane lipids. With the growth of MS use in clinical laboratories, a reliable MS-based glycolipid phenotyping method that identifies colistin resistance in A. baumannii complex clinical isolates, as well as other Gram-negative organisms, represents an alternative or complementary approach to existing diagnostics.

scholarly journals Corrected Genome Sequence of Acinetobacter baumannii Strain AB0057, an Antibiotic-Resistant Isolate from Lineage 1 of Global Clone 1

2017 ◽  
Vol 5 (35) ◽  
Author(s):  
Mohammad Hamidian ◽  
Pratap Venepally ◽  
Ruth M. Hall ◽  
Mark D. Adams
Keyword(s):  
United States ◽  
Acinetobacter Baumannii ◽  
Genome Sequence ◽  
The United States ◽  
Targeted Sequencing ◽  
Resistant Isolate ◽  
Illumina Hiseq ◽  
Antibiotic Resistant ◽  
Content Type ◽  
Pcr Products

ABSTRACT Extensively antibiotic-resistant Acinetobacter baumannii isolate AB0057 recovered in the United States in 2004 was one of the first global clone 1 isolates to be completely sequenced. Here, the complete 4.05-Mb genome sequence (chromosome and one plasmid) has been revised using Illumina HiSeq data and targeted sequencing of PCR products.

scholarly journals The Capsular Polysaccharide of Acinetobacter baumannii Is an Obstacle for Therapeutic Passive Immunization Strategies

2017 ◽  
Vol 85 (12) ◽  
Author(s):  
Shun Xin Wang-Lin ◽  
Ruth Olson ◽  
Janet M. Beanan ◽  
Ulrike MacDonald ◽  
Joseph P. Balthasar ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Outer Membrane ◽  
Bactericidal Activity ◽  
Capsular Polysaccharide ◽  
Rapid Development ◽  
Outer Membrane Proteins ◽  
Passive Immunization ◽  
Clinical Isolates ◽  
Content Type ◽  
Resistant Strains

ABSTRACT Acinetobacter baumannii has become an important concern for human health due to rapid development and wide spread of antimicrobial-resistant strains and high mortality associated with the infection. Passive immunizations with antisera targeting outer membrane proteins (OMPs) have shown encouraging results in protecting mice from A. baumannii infection, but monoclonal anti-OMP antibodies have not been developed, and their potential therapeutic properties have not been explored. The goal of this report is to evaluate the antibacterial activity of monoclonal antibodies (MAbs) targeting outer membrane protein A (OmpA) of A. baumannii. Five anti-OmpA MAbs were developed using hybridoma technology and showed strong binding to strain ATCC 19606. However, low antibody binding was observed when they were tested against six clinical isolates, which included extensively drug-resistant strains. In contrast, high binding to an isogenic K1 capsule-negative mutant (AB307.30) was shown, suggesting that capsular polysaccharide mediated the inhibition of MAb binding to OmpA. Anti-OmpA MAbs increased the macrophage-mediated bactericidal activity of AB307.30 but failed to increase phagocytic killing of capsule-positive strains. Capsular polysaccharide was also protective against complement-mediated bactericidal activity in human ascites in the presence and absence of opsonization. Lastly, passive immunization with anti-OmpA MAbs did not confer protection against challenge with AB307-0294, the encapsulated parent strain of AB307.30, in a mouse sepsis infection model. These results reveal the important role of capsule polysaccharide in shielding OmpA and thereby inhibiting anti-OmpA MAb binding to clinical isolates. This property of capsule hindered the therapeutic utility of anti-OmpA MAbs, and it may apply to other conserved epitopes in A. baumannii.

scholarly journals Multiplecyp51A-Based Mechanisms Identified in Azole-Resistant Isolates of Aspergillus fumigatus from China

2015 ◽  
Vol 59 (7) ◽  
pp. 4321-4325 ◽  
Author(s):  
Musang Liu ◽  
Rong Zeng ◽  
Lili Zhang ◽  
Dongmei Li ◽  
Guixia Lv ◽  
...  
Keyword(s):  
Aspergillus Fumigatus ◽  
Clinical Isolates ◽  
Resistant Isolate ◽  
Azole Resistance ◽  
Content Type ◽  
Resistant Strains

ABSTRACTSeventy-twoA. fumigatusclinical isolates from China were investigated for azole resistance based on mutations ofcyp51A. We identified four azole-resistant strains, among which we found three strains highly resistant to itraconazole, two of which exhibit the TR34/L98H/S297T/F495I mutation, while one carries only the TR34/L98H mutation. To our knowledge, the latter has not been found previously in China. The fourth multiazole-resistant isolate (with only moderate itraconazole resistance) carries a new G432A mutation.

scholarly journals Characterization of the Enterobacter Phage vB_EclM_CIP9

2020 ◽  
Vol 9 (13) ◽  
Author(s):  
Klara Wang ◽  
Marielou G. Tamayo ◽  
Tiffany V. Penner ◽  
Bradley W. M. Cook ◽  
Deborah A. Court ◽  
...  
Keyword(s):  
Enterobacter Cloacae ◽  
Opportunistic Pathogen ◽  
Multidrug Resistant ◽  
Open Reading Frames ◽  
Resistant Isolate ◽  
Content Type ◽  
Hospital Acquired Infections ◽  
Hospital Acquired ◽  
Reading Frames

Enterobacter cloacae is an opportunistic pathogen that causes hospital-acquired infections in immunocompromised patients. Here, we describe vB_EclM_CIP9, a novel Enterobacter phage that infects a multidrug-resistant isolate of E. cloacae. Phage vB_EclM_CIP9 is a myovirus that has a 174,924-bp genome, with 296 predicted open reading frames.

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