lipid-a and Acinetobacter-Infections

Acinetobacter baumannii is an opportunistic pathogen associated with nosocomial and community infections of great clinical relevance. Its ability to rapidly develop resistance to antimicrobials, especially carbapenems, has re-boosted the prescription and use of polymyxins. However, the emergence of strains resistant to these antimicrobials is becoming a critical issue in several regions of the world because very few of currently available antibiotics are effective in these cases. This review summarizes the most up-to-date knowledge about chromosomally encoded and plasmid-mediated polymyxins resistance in A. baumannii. Different mechanisms are employed by A. baumannii to overcome the antibacterial effects of polymyxins. Modification of the outer membrane through phosphoethanolamine addition, loss of lipopolysaccharide, symmetric rupture, metabolic changes affecting osmoprotective amino acids, and overexpression of efflux pumps are involved in this process. Several genetic elements modulate these mechanisms, but only three of them have been described so far in A. baumannii clinical isolates such as mutations in pmrCAB, lpxACD, and lpsB. Elucidation of genotypic profiles and resistance mechanisms are necessary for control and fight against resistance to polymyxins in A. baumannii, thereby protecting this class for future treatment.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Animals; Anti-Bacterial Agents; Bacterial Proteins; Chromosomes, Bacterial; Cross Infection; Drug Resistance, Multiple, Bacterial; Ethanolaminephosphotransferase; Humans; Lipid A; Lipopolysaccharides; Mice; Microbial Sensitivity Tests; Plasmids; Polymyxins; Public Health

Topics: Acinetobacter baumannii; Acinetobacter Infections; Colistin; Ethanolamines; Humans; Lipid A; Microbial Sensitivity Tests; Phosphatidylethanolamines; Sulbactam

To explore the significance of the resistance to polymyxin resistance of the extensively drug resistant. Tentyone were in the drug resistant group, accounting for 21 (29.17%,) and 51 were in the sensitive group, accounting for 70.83%. Some strains had mutations in

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Drug Resistance, Multiple, Bacterial; Drug Synergism; Humans; Lipid A; Lipopolysaccharides; Microbial Sensitivity Tests; Mutation; Polymyxins

LpxB is an enzyme involved in the biosynthesis pathway of lipid A, a component of LPS.. To evaluate the lpxB gene in Acinetobacter baumannii as a potential therapeutic target and to propose antisense agents such as peptide nucleic acids (PNAs) as a tool to combat bacterial infection, either alone or in combination with known antimicrobial therapies.. RNA-seq analysis of the A. baumannii ATCC 17978 strain in a murine pneumonia model was performed to study the in vivo expression of lpxB. Protein expression was studied in the presence or absence of anti-lpxB (KFF)3K-PNA (pPNA). Time-kill curve analyses and protection assays of infected A549 cells were performed. The chequerboard technique was used to test for synergy between pPNA and colistin. A Galleria mellonella infection model was used to test the in vivo efficacy of pPNA.. The lpxB gene was overexpressed during pneumonia. Treatment with a specific pPNA inhibited LpxB expression in vitro, decreased survival of the ATCC 17978 strain and increased the survival rate of infected A549 cells. Synergy was observed between pPNA and colistin in colistin-susceptible strains. In vivo assays confirmed that a combination treatment of anti-lpxB pPNA and colistin was more effective than colistin in monotherapy.. The lpxB gene is essential for A. baumannii survival. Anti-lpxB pPNA inhibits LpxB expression, causing bacterial death. This pPNA showed synergy with colistin and increased the survival rate in G. mellonella. The data suggest that antisense pPNA molecules blocking the lpxB gene could be used as antibacterial agents.

Topics: A549 Cells; Acinetobacter baumannii; Acinetobacter Infections; Animals; Anti-Bacterial Agents; Bacterial Proteins; Biosynthetic Pathways; Colistin; DNA, Antisense; Drug Synergism; Gene Expression; Humans; Lipid A; Male; Mice; Mice, Inbred BALB C; Microbial Sensitivity Tests; Moths; Peptide Nucleic Acids; RNA-Seq

Multidrug resistant (MDR) strains of Acinetobacter baumannii present a serious clinical challenge. The development of antibiotic resistance in this species is enabled by efflux pumps of the Resistance-Nodulation-Division (RND) superfamily of proteins creating an efficient permeability barrier for antibiotics. At least three RND pumps, AdeABC, AdeIJK, and AdeFGH are encoded in the A. baumannii genome and are reported to contribute to antibiotic resistance in clinical isolates. In this study, we analyzed the contributions of AdeABC and AdeIJK in antibiotic resistance and growth physiology of the two MDR strains, AYE and AB5075. We found that not only the two pumps have nonoverlapping substrate specificities, their inactivation leads to specific nonoverlapping changes in gene expression as determined by RNA sequencing and confirmed by gene knockouts and growth phenotypes. Our results suggest that inactivation of AdeIJK elicits broader changes in the abundances of mRNAs and this response is modified in the absence of AdeB. In contrast, inactivation of AdeB leads to a focused cellular response, which is not sensitive to the activity of AdeIJK. We identified additional efflux pumps and transcriptional regulators that contribute to MDR phenotype of clinical A. baumannii isolates.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Bacterial Proteins; Drug Resistance, Multiple, Bacterial; Gene Expression Regulation, Bacterial; Gene Knockout Techniques; Lipid A; Membrane Transport Proteins; Microbial Sensitivity Tests; Phenotype; RNA, Bacterial; Sequence Analysis, RNA; Substrate Specificity

Colistin resistance in

Topics: Acinetobacter baumannii; Acinetobacter Infections; Animals; Anti-Bacterial Agents; Bacterial Proteins; Colistin; Disease Models, Animal; Drug Resistance, Bacterial; Humans; Lipid A; Microbial Sensitivity Tests; Moths; Transcription Factors

The increasing incidence and emergence of multi-drug resistant (MDR) Acinetobacter baumannii has become a major global health concern. Colistin is a historic antimicrobial that has become commonly used as a treatment for MDR A. baumannii infections. The increase in colistin usage has been mirrored by an increase in colistin resistance. We aimed to identify the mechanisms associated with colistin resistance in A. baumannii using multiple high-throughput-sequencing technologies, including transposon-directed insertion site sequencing (TraDIS), RNA sequencing (RNAseq) and whole-genome sequencing (WGS) to investigate the genotypic changes of colistin resistance in A. baumannii. Using TraDIS, we found that genes involved in drug efflux (adeIJK), and phospholipid (mlaC, mlaF and mlaD) and lipooligosaccharide synthesis (lpxC and lpsO) were required for survival in sub-inhibitory concentrations of colistin. Transcriptomic (RNAseq) analysis revealed that expression of genes encoding efflux proteins (adeI, adeC, emrB, mexB and macAB) was enhanced in in vitro generated colistin-resistant strains. WGS of these organisms identified disruptions in genes involved in lipid A (lpxC) and phospholipid synthesis (mlaA), and in the baeS/R two-component system (TCS). We additionally found that mutations in the pmrB TCS genes were the primary colistin-resistance-associated mechanisms in three Vietnamese clinical colistin-resistant A. baumannii strains. Our results outline the entire range of mechanisms employed in A. baumannii for resistance against colistin, including drug extrusion and the loss of lipid A moieties by gene disruption or modification.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Bacterial Proteins; Colistin; Drug Resistance, Bacterial; High-Throughput Nucleotide Sequencing; Lipid A; Mutation; Phospholipids; Vietnam

Topics: Acinetobacter baumannii; Acinetobacter Infections; Acyltransferases; Animals; Bacterial Proteins; Humans; Hydroxylation; Larva; Lipid A; Male; Mice; Mice, Inbred C57BL; Moths; Virulence

The increasing morbidity and mortality rates associated with Acinetobacter baumannii are due to the emergence of drug resistance and the limited treatment options. We compared characteristics of colistin-resistant Acinetobacter baumannii (CR-AB) clinical isolates recovered from patients with and without prior colistin treatment. We assessed whether prior colistin treatment affects the resistance mechanism of CR-AB isolates, mortality rates, and clinical characteristics. Additionally, a proper method for identifying CR-AB was determined.. We collected 36 non-duplicate CR-AB clinical isolates resistant to colistin. Antimicrobial susceptibility testing, Sanger sequencing analysis, molecular typing, lipid A structure analysis, and in vitro synergy testing were performed. Eleven colistin-susceptible AB isolates were used as controls.. Despite no differences in clinical characteristics between patients with and without prior colistin treatment, resistance-causing genetic mutations were more frequent in isolates from colistin-treated patients. Distinct mutations were overlooked via the Sanger sequencing method, perhaps because of a masking effect by the colistin-susceptible AB subpopulation of CR-AB isolates lacking genetic mutations. However, modified lipid A analysis revealed colistin resistance peaks, despite the population heterogeneity, and peak levels were significantly different between the groups.. Although prior colistin use did not induce clinical or susceptibility differences, we demonstrated that identification of CR-AB by sequencing is insufficient. We propose that population heterogeneity has a masking effect, especially in colistin non-treated patients; therefore, accurate testing methods reflecting physiological alterations of the bacteria, such as phosphoethanolamine-modified lipid A identification by matrix-assisted laser desorption ionization-time of flight, should be employed.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Adolescent; Adult; Aged; Anti-Bacterial Agents; Anti-Infective Agents; Colistin; DNA, Bacterial; Drug Resistance, Bacterial; Electrophoresis, Gel, Pulsed-Field; Female; Humans; Lipid A; Male; Microbial Sensitivity Tests; Middle Aged; Multilocus Sequence Typing; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Young Adult

With an increase in the use of colistin methansulfonate (CMS) to treat carbapenem-resistant Acinetobacter baumannii infections, colistin resistance is emerging.. Patients with infection or colonization due to colistin-resistant A. baumannii were identified at a hospital system in Pennsylvania. Clinical data were collected from electronic medical records. Susceptibility testing, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST) were performed. To investigate the mechanism of colistin resistance, lipid A was subjected to matrix-assisted laser desorption/ionization mass spectrometry.. Twenty patients with colistin-resistant A. baumannii were identified. Ventilator-associated pneumonia was the most common type of infection. Nineteen patients had received intravenous and/or inhaled CMS for treatment of carbapenem-resistant, colistin-susceptible A. baumannii infection prior to identification of colistin-resistant isolates. The 30-day all-cause mortality rate was 30%. The treatment regimen for colistin-resistant A. baumannii infection associated with the lowest mortality rate was a combination of CMS, a carbapenem, and ampicillin-sulbactam. The colistin-susceptible and -resistant isolates from the same patients were highly related by PFGE, but isolates from different patients were not, suggesting evolution of resistance during CMS therapy. By MLST, all isolates belonged to the international clone II, the lineage that is epidemic worldwide. Phosphoethanolamine modification of lipid A was present in all colistin-resistant A. baumannii isolates.. Colistin-resistant A. baumannii occurred almost exclusively among patients who had received CMS for treatment of carbapenem-resistant, colistin-susceptible A. baumannii infection. Lipid A modification by the addition of phosphoethanolamine accounted for colistin resistance. Susceptibility testing for colistin should be considered for A. baumannii identified from CMS-experienced patients.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Adult; Aged; Aged, 80 and over; Ampicillin; Carbapenems; Colistin; Drug Resistance, Multiple, Bacterial; Electronic Health Records; Electrophoresis, Gel, Pulsed-Field; Ethanolamines; Female; Humans; Lipid A; Male; Microbial Sensitivity Tests; Middle Aged; Multilocus Sequence Typing; Pneumonia, Ventilator-Associated; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Sulbactam

The emergence of colistin-resistant Acinetobacter baumannii is concerning, as colistin is often regarded as the last option for treating multidrug-resistant (MDR) A. baumannii infections. Using mRNA sequencing, we compared whole transcriptomes of colistin-susceptible and colistin-resistant A. baumannii strains, with the aim of identifying genes involved in colistin resistance. A clinical colistin-susceptible strain (06AC-179) and a colistin-resistant strain (07AC-052) were analysed in this study. In addition, a colistin-resistant mutant (06AC-179-R1) derived from 06AC-179 was also included in this study. High throughput mRNA sequencing was performed with an Illumina HiSeq TM 2000. In total, six genes were identified as associated with colistin resistance in A. baumannii. These six genes encode PmrAB two-component regulatory enzymes, PmrC (a lipid A phosphoethanolamine transferase), a glycosyltransferase, a poly-β-1,6-N-acetylglucosamine deacetylase, and a putative membrane protein. Matrix-assisted laser desorption/ionization time of flight mass spectrometry revealed that all three colistin-resistant strains used in this study had modified lipid A structure by addition of phosphoethanolamine. As genes found in our results are all associated with either lipopolysaccharide biosynthesis or electrostatic changes in the bacterial cell membrane, lipopolysaccharide modification might be one of the principal modes of acquisition of colistin resistance in some A. baumannii strains.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Colistin; Drug Resistance, Bacterial; Gene Expression Profiling; Genes, Bacterial; High-Throughput Nucleotide Sequencing; Humans; Lipid A; Sequence Analysis, DNA; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

Treatment options for multidrug-resistant (MDR) strains of Acinetobacter baumannii that acquire resistance to colistin are limited. Acinetobacter baumannii can become highly resistant to colistin through complete loss of lipopolysaccharide (LPS) owing to mutations in the genes encoding the first three enzymes involved in lipid A biosynthesis (lpxA, lpxC and lpxD). The objective of this study was to characterise the susceptibility to 15 clinically relevant antibiotics and 6 antimicrobial peptides (AMPs) of MDR A. baumannii clinical isolates that acquired colistin resistance due to mutations in lpxA, lpxC and lpxD as well as their colistin-susceptible counterparts. A dramatic increase in antibiotic susceptibility (≥16-fold increase) was observed upon LPS loss for azithromycin, rifampicin and vancomycin, whereas a moderate increase in susceptibility was seen for amikacin, ceftazidime, imipenem, cefepime and meropenem. Importantly, concentrations ranging from 8 mg/L to 32 mg/L of the six AMPs were able to reduce bacterial viability by ≥3 log10 in growth curve assays. We also demonstrate that colistin resistance results in partial colistin dependence for growth in LPS-deficient strains containing mutations in lpxA, lpxC and lpxD, but not when colistin resistance occurs via LPS modification due to mutations in the PmrA/B two-component system. The results of this study indicate that loss of LPS expression results in collateral sensitivity to azithromycin, rifampicin and vancomycin, and that the six AMPs tested retain activity against LPS-deficient strains, indicating that these antibiotics may be viable treatment options for infections caused by these strains.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Azithromycin; Bacterial Proteins; Colistin; Drug Resistance, Multiple, Bacterial; Humans; Lipid A; Lipopolysaccharides; Microbial Sensitivity Tests; Microbial Viability; Rifampin; Vancomycin

Emerging resistance to "last-resort" polymyxin antibiotics in Gram-negative bacteria is a significant threat to public health. We identified the Acinetobacter baumannii NaxD deacetylase as a critical mediator of lipid A modification resulting in polymyxin resistance and demonstrated that naxD is regulated by the sensor kinase PmrB. This represents the first description of a specific PmrB-regulated gene contributing to polymyxin resistance in A. baumannii and highlights NaxD as a putative drug target to reverse polymyxin resistance.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Amidohydrolases; Anti-Bacterial Agents; Bacterial Proteins; Drug Resistance, Bacterial; Gene Expression Regulation, Bacterial; Humans; Lipid A; Microbial Sensitivity Tests; Molecular Structure; Polymyxin B; Transcription Factors

New structural amphiphiles 2a and 2b bind the diphosphate lipid A anion and show potential as lead compounds for the development of novel antibacterial agents.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Anions; Anti-Bacterial Agents; Erythrocytes; Gram-Negative Bacteria; Humans; Lipid A; Microbial Sensitivity Tests; Models, Molecular; Pseudomonas aeruginosa; Pseudomonas Infections; Surface-Active Agents