Conformational stability of OXA-51 β-lactamase explains its role in carbapenem resistance of Acinetobacter baumannii

Structural and Dynamic Features of Acinetobacter baumannii OXA-66 β-Lactamase Explain Its Stability and Evolution of Novel Variants

OXA-66 is a member of the OXA-51 subfamily of class D β-lactamases native to the Acinetobacter genus that includes Acinetobacter baumannii, one of the ESKAPE pathogens and a major cause of drug-resistant nosocomial infections. Although both wild type OXA-66 and OXA-51 have low catalytic activity, they are ubiquitous in the Acinetobacter genomes. OXA-51 is also remarkably thermostable. In addition, newly emerging, single and double amino acid variants show increased activity against carbapenems, indicating that the OXA-51 subfamily is growing and gaining clinical significance. In this study, we used molecular dynamics simulations, X-ray crystallography, and thermal denaturation data to examine and compare the dynamics of OXA-66 wt and its gain-of-function variants: I129L (OXA-83), L167V (OXA-82), P130Q (OXA-109), P130A, and W222L (OXA-234). Our data indicate that OXA-66 wt also has a high melting temperature, and its remarkable stability is due to an extensive and rigid hydrophobic bridge formed by a number of residues around the active site and harbored by the three loops, P, Ω, and β5-β6. Compared to the WT enzyme, the mutants exhibit higher flexibility only in the loop regions, and are more stable than other robust carbapenemases, such as OXA-23 and OXA-24/40. All the mutants show increased rotational flexibility of residues I129 and W222, which allows carbapenems to bind. Overall, our data support the hypothesis that structural features in OXA-51 and OXA-66 promote evolution of multiple highly stable variants with increased clinical relevance in A. baumannii.

Interaction and simulation studies suggest the possible molecular targets of intrinsically disordered amyloidogenic antimicrobial peptides in Acinetobacter baumannii

Acinetobacter baumannii is one of the causing agents of nosocomial infections. A wide range of antibiotics fails to work against these pathogens. Hence, there is an urgent requirement to develop other therapeutics to solve this problem. Antimicrobial peptides (AMPs) are a diverse group of naturally occurring peptides that have the ability to kill diverse groups of microorganisms. The major challenge of using AMPs as therapeutics is their unstable nature and the fact that most of their molecular targets are still unknown. In this study, we have selected intrinsically disordered and amyloidogenic AMPs, showing activity against A. baumannii, that is, Bactenecin, Cath BF, Citropin 1.1, DP7, NA-CATH, Tachyplesin, and WAM-1. To identify the probable target of these AMPs in A. baumannii, calculation of docking score, binding energy, dissociation constant, and molecular dynamics analysis was performed with selected seventeen possible molecular targets. The result showed that the most probable molecular targets of most of the intrinsically disordered amyloidogenic AMPs were UDP-N-acetylenol-pyruvoyl-glucosamine reductase (MurB), followed by 33-36 kDa outer membrane protein (Omp 33-36), UDP-N-acetylmuramoyl-l-alanyl-d-glutamate-2,6-diaminopimelate ligase (MurE), and porin Subfamily Protein (PorinSubF). Further, molecular dynamics analysis concluded that the target of antimicrobial peptide Bactenecin is MurB of A. baumannii, and identified other molecular targets of selected AMPs. Additionally, the oligomerization capacity of the selected AMPs was also investigated, and it was shown that the selected AMPs form oligomeric states, and interact with their molecular targets in that state. Experimental validation using purified AMPs and molecular targets needs to be done to confirm the interaction.Communicated by Ramaswamy H. Sarma.

Bacteriophage therapy against ESKAPE bacterial pathogens: Current status, strategies, challenges, and future scope

The ESKAPE pathogens are the primary threat due to their constant spread of drug resistance worldwide. These pathogens are also regarded as opportunistic pathogens and could potentially cause nosocomial infections. Most of the ESKAPE pathogens have developed resistance to almost all the antibiotics that are used against them. Therefore, to deal with antimicrobial resistance, there is an urgent requirement for alternative non-antibiotic strategies to combat this rising issue of drug-resistant organisms. One of the promising alternatives to this scenario is implementing bacteriophage therapy. This under-explored mode of treatment in modern medicine has posed several concerns, such as preferable phages for the treatment, impact on the microbiome (or gut microflora), dose optimisation, safety, etc. The review will cover a rationale for phage therapy, clinical challenges, and propose phage therapy as an effective therapeutic against bacterial coinfections during pandemics. This review also addresses the expected uncertainties for administering the phage as a treatment against the ESKAPE pathogens and the advantages of using lytic phage over temperate, the immune response to phages, and phages in combinational therapies. The interaction between bacteria and bacteriophages in humans and countless animal models can also be used to design novel and futuristic therapeutics like personalised medicine or bacteriophages as anti-biofilm agents. Hence, this review explores different aspects of phage therapy and its potential to emerge as a frontline therapy against the ESKAPE bacterial pathogen.

Acinetobacter baumannii in suspected bacterial infections: Association between multidrug resistance, virulence genes, & biofilm production

BACKGROUND OBJECTIVES

Acinetobacter baumannii has emerged as a nosocomial pathogen with a tendency of high antibiotic resistance and biofilm production. This study aimed to determine the occurrence of A. baumannii from different clinical specimens of suspected bacterial infections and furthermore to see the association of biofilm production with multidrug resistance and expression of virulence factor genes in A. baumannii.

METHODS

A. baumannii was confirmed in clinical specimens by the detection of the blaOXA-51-like gene. Biofilm production was tested by microtitre plate assay and virulence genes were detected by real-time PCR.

RESULTS

A. baumannii was isolated from a total of 307 clinical specimens. The isolate which showed the highest number of A. baumannii was an endotracheal tube specimen (44.95%), then sputum (19.54%), followed by pus (17.26%), urine (7.49%) and blood (5.86%), and <2 per cent from body fluids, catheter-tips and urogenital specimens. A resistance rate of 70-81.43 per cent against all antibiotics tested, except colistin and tigecycline, was noted, and 242 (78.82%) isolates were multidrug-resistant (MDR). Biofilm was detected in 205 (66.78%) with a distribution of 54.1 per cent weak, 10.42 per cent medium and 2.28 per cent strong biofilms. 71.07 per cent of MDR isolates produce biofilm (P<0.05). Amongst virulence factor genes, 281 (91.53%) outer membrane protein A (OmpA) and 98 (31.92%) biofilm-associated protein (Bap) were detected. Amongst 100 carbapenem-resistant A. baumannii, the blaOXA-23-like gene was predominant (96%), the blaOXA-58-like gene (6%) and none harboured the blaOXA-24-like gene. The metallo-β-lactamase genes blaIMP-1 (4%) and blaVIM-1(8%) were detected, and 76 per cent showed the insertion sequence ISAba1.

INTERPRETATION CONCLUSIONS

The majority of isolates studied were from lower respiratory tract specimens. The high MDR rate and its positive association with biofilm formation indicate the nosocomial distribution of A. baumannii. The biofilm formation and the presence of Bap were not interrelated, indicating that biofilm formation was not regulated by a single factor. The MDR rate and the presence of OmpA and Bap showed a positive association (P<0.05). The isolates co-harbouring different carbapenem resistance genes were the predominant biofilm producers, which will seriously limit the therapeutic options suggesting the need for strict antimicrobial stewardship and molecular surveillance in hospitals.

Investigation of Peptidoglycan-Associated Lipoprotein of Acinetobacter baumannii and Its Interaction with Fibronectin To Find Its Therapeutic Potential

Acinetobacter baumannii causes hospital-acquired infections and is responsible for high mortality and morbidity. The interaction of this bacterium with the host is critical in bacterial pathogenesis and infection. Here, we report the interaction of peptidoglycan-associated lipoprotein (PAL) of A. baumannii with host fibronectin (FN) to find its therapeutic potential. The proteome of A. baumannii was explored in the host-pathogen interaction database to filter out the PAL of the bacterial outer membrane that interacts with the host's FN protein. This interaction was confirmed experimentally using purified recombinant PAL and pure FN protein. To investigate the pleiotropic role of PAL protein, different biochemical assays using wild-type PAL and PAL mutants were performed. The result showed that PAL mediates bacterial pathogenesis, adherence, and invasion in host pulmonary epithelial cells and has a role in the biofilm formation, bacterial motility, and membrane integrity of bacteria. All of the results suggest that PAL's interaction with FN plays a vital role in host-cell interaction. In addition, the PAL protein also interacts with Toll-like receptor 2 and MARCO receptor, which suggests the role of PAL protein in innate immune responses. We have also investigated the therapeutic potential of this protein for vaccine and therapeutic design. Using reverse vaccinology, PAL's potential epitopes were filtered out that exhibit binding potential with host major histocompatibility complex class I (MHC-I), MHC-II, and B cells, suggesting that PAL protein is a potential vaccine target. The immune simulation showed that PAL protein could elevate innate and adaptive immune response with the generation of memory cells and would have subsequent potential to eliminate bacterial infection. Therefore, the present study highlights the interaction ability of a novel host-pathogen interacting partner (PAL-FN) and uncovers its therapeutic potential to combat infection caused by A. baumannii.

CRISPR-Cas in Acinetobacter baumannii Contributes to Antibiotic Susceptibility by Targeting Endogenous AbaI

Acinetobacter baumannii is a well-known human opportunistic pathogen in nosocomial infections, and the emergence of multidrug-resistant Acinetobacter baumannii has become a complex problem for clinical anti-infective treatments. The ways this organism obtains multidrug resistance phenotype include horizontal gene transfer and other mechanisms, such as altered targets, decreased permeability, increased enzyme production, overexpression of efflux pumps, metabolic changes, and biofilm formation. A CRISPR-Cas system generally consists of a CRISPR array and one or more operons of cas genes, which can restrict horizontal gene transfer in bacteria. Nevertheless, it is unclear how CRISPR-Cas systems regulate antibiotic resistance in Acinetobacter baumannii. Thus, we sought to assess how CRISPR-Cas affects biofilm formation, membrane permeability, efflux pump, reactive oxygen species, and quorum sensing to clarify further the mechanism of CRISPR-Cas regulation of Acinetobacter baumannii antibiotic resistance. In the clinical isolate AB43, which has a complete I-Fb CRISPR-Cas system, we discovered that the Cas3 nuclease of this type I-F CRISPR-Cas system regulates Acinetobacter baumannii quorum sensing and has a unique function in changing drug resistance. As a result of quorum sensing, synthase abaI is reduced, allowing efflux pumps to decrease, biofilm formation to become weaker, reactive oxygen species to generate, and drug resistance to decrease in response to CRISPR-Cas activity. These observations suggest that the CRISPR-Cas system targeting endogenous abaI may boost bacterial antibiotic sensitivity.

IMPORTANCE CRISPR-Cas systems are vital for genome editing, bacterial virulence, and antibiotic resistance. How CRISPR-Cas systems regulate antibiotic resistance in Acinetobacter baumannii is almost wholly unknown. In this study, we reveal that the quorum sensing regulator abaI mRNA was a primary target of the I-Fb CRISPR-Cas system and the cleavage activity of Cas3 was the most critical factor in regulating abaI mRNA degradation. These results advance our understanding of how CRISPR-Cas systems inhibit drug resistance. However, the mechanism of endogenous targeting of abaI by CRISPR-Cas needs to be further explored.

Pharmacophore screening, denovo designing, retrosynthetic analysis, and combinatorial synthesis of a novel lead VTRA1.1 against RecA protein of Acinetobacter baumannii

Antibiotics and disinfectants resistance is acquired by activating RecA-mediated DNA repair, which maintains ROS-dependent DNA damage caused by the antimicrobial molecules. To increase the efficacy of different antimicrobials, an inhibitor can be developed against RecA protein. The present study aims to design a denovo inhibitor against RecA protein of Acinetobacter baumannii. Pharmacophore-based screening, molecular mechanics, molecular dynamics simulation (MDS), retrosynthetic analysis, and combinatorial synthesis were used to design lead VTRA1.1 against RecA of A. baumannii. Pharmacophore models (structure-based and ligand-based) were created, and a phase library of FDA-approved drugs was prepared. Screening of the phase library against these pharmacophore models selected thirteen lead molecules. These filtered leads were used for the denovo fragment-based design, which produced 253 combinations. These designed molecules were further analyzed for its interaction with active site of RecA that selected a hybrid VTRA1. Further, retrosynthetic analysis and combinatorial synthesis produced 1000 analogs of VTRA1 by more than 100 modifications. These analogs were used for XP docking, binding free energy calculation, and MDS analysis which finally select lead VTRA1.1 against RecA protein. Further, mutations at the interacting residues of RecA with VTRA1.1, alter the unfolding rate of RecA, which suggests the binding of VTRA1.1 to these residues may alter the stability of RecA. It is also found that VTRA1.1 had reduced interaction of RecA with LexA and ssDNA polydT, showing the lead's efficacy in controlling the SOS response. Further, it was also observed that VTRA1.1 does not contain any predicted human off-targets and no cytotoxicity to cell lines. As functional RecA is involved in antimicrobial resistance, denovo designed lead VTRA1.1 against RecA may be further developed as a significant combination for therapeutic uses against A. baumannii.

Therapeutic strategies against potential antibiofilm targets of multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii is the causative agent of various hospital-acquired infections. Biofilm formation is one of the various antimicrobial resistance (AMR) strategies and is associated with high mortality and morbidity. Hence, it is essential to review the potential antibiofilm targets in A. baumannii and come up with different strategies to combat these potential targets. This review covers different pathways involved in the regulation of biofilm formation in A. baumannii like quorum sensing (QS), cyclic-di-GMP signaling, two-component system (TCS), outer-membrane protein (ompA), and biofilm-associated protein (BAP). A newly discovered mechanism of electrical signaling-mediated biofilm formation and contact-dependent biofilm modulation has also been discussed. As biofilm formation and its maintenance in A. baumannii is facilitated by these potential targets, the detailed study of these targets and pathways can bring light to different therapeutic strategies such as anti-biofilm peptides, natural and synthetic molecule inhibitors, QS molecule degrading enzymes, and other strategies. These strategies may help in suppressing the lethality of biofilm-mediated infections. Targeting essential proteins/targets which are crucial for biofilm formation and regulation may render new therapeutic strategies that can aid in combating biofilm, thus reducing the recalcitrant infections and morbidity associated with the biofilm of A. baumannii.

Anti-persister strategies against stress induced bacterial persistence

The increase in antibiotic non-responsive bacteria is the leading concern in current research-oriented to eliminate pathogens. Nowadays, the excess use of antibiotics without specifically understanding the potentiality of killing pathogens and bacterial survival patterns has helped bacteria emerge indefatigably. Bacteria use various mechanisms such as resistance, persistence, and tolerance to ensure survival. Among these, persistence is a mechanism by which bacteria reside in their dormant state, bypassing the effects of treatments, making it crucial for bacterial survival. Persistent bacterial cells arise from the normal bacterial population as a slow-growing subset of bacteria with no metabolic flux. This behavior renders it to survive for a longer duration and at higher concentrations of antibiotics. They are one of the underlying causes of recurrence of bacterial infections. The present article explains the detailed molecular mechanisms and strategies of bacterial persistence, including the toxin-antitoxin modules, DNA damage, the formation of inactive ribosomal complexes, (p)ppGpp network, antibiotic-induced persistence, which are triggered by drug-induced stress. The article also comprehensively covers the epigenetic memory of persistence in bacteria, and anti-persistent therapeutics like antimicrobial molecules, synthetic peptides, acyldepsipeptide antibiotics, and endolysin therapy to reduce persister cell formation and control their frequency. These strategies could be utilized in combating the pathogenic bacteria undergoing persistence.

Efflux pumps in multidrug-resistant Acinetobacter baumannii: Current status and challenges in the discovery of efflux pumps inhibitors

Acinetobacter baumannii is an ESKAPE pathogen known to cause fatal nosocomial infections. With the surge of multidrug resistance (MDR) in the bacterial system, effective treatment measures have become very limited. The MDR in A. baumannii is contributed by various factors out of which efflux pumps have gained major attention due to their broad substrate specificity and wide distribution among bacterial species. The efflux pumps are involved in the MDR as well as contribute to other physiological processes in bacteria, therefore, it is critically important to inhibit efflux pumps in order to combat emerging resistance. The present review provides insight about the different efflux pump systems in A. baumannii and their role in multidrug resistance. A major focus has been put on the different strategies and alternate therapeutics to inhibit the efflux system. This includes use of different efflux pump inhibitors-natural, synthetic or combinatorial therapy. The use of phage therapy and nanoparticles for inhibiting efflux pumps have also been discussed here. Moreover, the present review provides the knowledge of barriers in development of efflux pump inhibitors (EPIs) and their approval for commercialization. Here, different prospectives have been discussed to improve the therapeutic development process and make it more compatible for clinical use.

Carbapenemases: Transforming Acinetobacter baumannii into a Yet More Dangerous Menace

Acinetobacter baumannii is a common cause of serious nosocomial infections. Although community-acquired infections are observed, the vast majority occur in people with preexisting comorbidities. A. baumannii emerged as a problematic pathogen in the 1980s when an increase in virulence, difficulty in treatment due to drug resistance, and opportunities for infection turned it into one of the most important threats to human health. Some of the clinical manifestations of A. baumannii nosocomial infection are pneumonia; bloodstream infections; lower respiratory tract, urinary tract, and wound infections; burn infections; skin and soft tissue infections (including necrotizing fasciitis); meningitis; osteomyelitis; and endocarditis. A. baumannii has an extraordinary genetic plasticity that results in a high capacity to acquire antimicrobial resistance traits. In particular, acquisition of resistance to carbapenems, which are among the antimicrobials of last resort for treatment of multidrug infections, is increasing among A. baumannii strains compounding the problem of nosocomial infections caused by this pathogen. It is not uncommon to find multidrug-resistant (MDR, resistance to at least three classes of antimicrobials), extensively drug-resistant (XDR, MDR plus resistance to carbapenems), and pan-drug-resistant (PDR, XDR plus resistance to polymyxins) nosocomial isolates that are hard to treat with the currently available drugs. In this article we review the acquired resistance to carbapenems by A. baumannii. We describe the enzymes within the OXA, NDM, VIM, IMP, and KPC groups of carbapenemases and the coding genes found in A. baumannii clinical isolates.

Molecular mechanism of antimicrobial activity of chlorhexidine against carbapenem-resistant Acinetobacter baumannii

Acinetobacter baumannii causes hospital-acquired infections, especially in those with impaired immune function. Biocides or disinfectants are widely used antibacterial agents used to eradicate the effect of A. baumannii on inanimate objects and health care environments. In the current study, the antimicrobial activity of chlorhexidine has been investigated against carbapenem-resistant (RS-307, RS-7434, RS-6694, and RS-122), and sensitive (ATCC-19606 and RS-10953) strains of A. baumannii. We have determined growth kinetics, antimicrobial susceptibility, ROS production, lipid peroxidation, cell viability using flow cytometry assay (FACS), and membrane integrity by scanning electron microscope (SEM). The effect of chlorhexidine on the bacterial membrane has also been investigated using Fourier transform infrared (FTIR) spectroscopy. The present study showed that 32μg/ml chlorhexidine treatment results in the decreased bacterial growth, CFU count and cell viability. The antibacterial activity of chlorhexidine is due to the elevated ROS production and higher lipid peroxidation. These biochemical changes result in the membrane damage and alteration in the membrane proteins, phospholipids, carbohydrates, nucleic acids as evident from the FTIR and SEM data. Therefore, chlorhexidine has the potential to be used in the hospital setups to remove the spread of A. baumannii.

Molecular insight into the therapeutic potential of phytoconstituents targeting protein conformation and their expression

BACKGROUND

Native protein conformation is essential for the functional activity of the proteins and enzymes. Defects in conformation or alterations in expression of the proteins have been reported in various diseases.

PURPOSE

The aim of this study is to review the molecular insight into the therapeutic potential of phytoconstituents targeting protein conformations or expressions.

METHODS

Published literatures were searched in PubMed, Scopus, Web of Science; Article published till Dec 2017 were extracted. The literature was assessed from the Central University of Rajasthan, India. Present study evaluate article based on the role of active plant constituents on the conformation and expression of the different proteins.

RESULTS

Plant components play their role either at the molecular level or cellular level and exhibit antibacterial, antiviral, anti-neurodegenerative and other activities. Plant active compounds isolated from different plants may either stabilize or destabilize the conformation of proteins or alter expression level of the protein involved in these diseases, therefore, can play a significant role in preventing diseases caused by the alteration in these proteins.

CONCLUSION

In the present article, we have reviewed the molecular mechanism of plant active compounds, their target proteins, methods of extraction and identification, and their biological significances. Therefore, a proper understanding of the effect of these herbal molecules on the concerned proteins may help to develop new herbal-based therapeutics for various diseases.

Proteomic analysis of iron-regulated membrane proteins identify FhuE receptor as a target to inhibit siderophore-mediated iron acquisition in Acinetobacter baumannii

Survival of the Acinetobacter baumannii inside host requires different micronutrients such as iron, but their bioavailability is limited because of nutritional immunity created by host. A. baumannii has to develop mechanisms to acquire nutrient iron during infection. The present study is an attempt to identify membrane proteins involved in iron sequestration mechanism of A. baumannii using two-dimensional electrophoresis and LC-MS/MS analysis. The identified iron-regulated membrane protein (IRMP) of A. baumannii was used for its interaction studies with different siderophores, and designing of the inhibitor against A. baumannii targeting this IRMP. Membrane proteomic results identified over-expression of four membrane proteins (Fhu-E receptor, ferric-acinetobactin receptor, ferrienterochelin receptor, and ferric siderophore receptor) under iron-limited condition. A. baumannii produces siderophores that have good interaction with the FhuE receptor. Result also showed that FhuE receptor has interaction with siderophores produced by other bacteria. Interaction of FhuE receptor and siderophores helps in iron sequestration and survival of Acinetobacter under nutritional immunity imposed by the host. Hence it becomes essential to find a potential inhibitor for the FhuE receptor that can inhibit the survival of A. baumannii in the host. In-silico screening, and molecular mechanics studies identified ZINC03794794 and ZINC01530652 as a likely lead to design inhibitor against the FhuE receptor of A. baumannii. The designed inhibitor is experimentally validated for its antibacterial activity on the A. baumannii. Therefore, designed inhibitor interferes with the iron acquisition mechanism of Acinetobacter hence may prove useful for preventing infection caused by A. baumannii by limiting nutrient availability.

Comparative mechanism based study on disinfectants against multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii has emerged as a hospital-acquired pathogen and has spread in the hospital settings, leading to enhanced nosocomial outbreaks associated with high death rates. Therefore, the aim of the current study is to determine the effective concentration of disinfectants like sodium hypochlorite, hydrogen peroxide, and chlorine dioxide, against multidrug-resistant (MDR) strains of A. baumannii. In this study, we have investigated the effect of disinfectants on different MDR strains i.e. RS307, RS6694, RS7434, RS10953, RS122, and sensitive strain ATCC-19606 of A. baumannii, via differential growth curves analysis, disc diffusion assay, estimation of reactive oxygen species (ROS), lipid peroxidation, and protein carbonylation. All the results collectively showed that 1% sodium hypochlorite (P value < 0.0027), 2.5% hydrogen peroxide (P value = 0.0032), and 10 mM (P value = 0.017) chlorine dioxide significantly inhibit the growth of MDR strains of A. baumannii. A significant increase in the ROS generations, altered lipid peroxidation, and a decrease in protein carbonylation was also observed after treatment with disinfectants, which confirmed its ROS-dependent damage mechanism. These disinfectants also enhance the membrane leakage of reducing sugar, protein, and DNA. The current study highlights and recommends the use of 2.5% hydrogen peroxide to control the MDR strains of A. baumannii in the hospital setup. Therefore, the present results will help in selecting concentrations of different disinfectants for regular use in hospital setups to eradicate the multidrug-resistant A. baumannii from the hospital setup.

Targeting Outer Membrane Protein Component AdeC for the Discovery of Efflux Pump Inhibitor against AdeABC Efflux Pump of Multidrug Resistant Acinetobacter baumannii

The structure and functioning of multidrug efflux systems provide us with a better understanding of the transport of various antibiotics, thus giving a path for the discovery of effective compounds for combating the multidrug resistance in Acinetobacter baumannii. In the present study, a number of computational techniques have been used to search for an inhibitor for the RND efflux pump, AdeABC, of A. baumannii targeting specifically its outermost component, i.e., AdeC. We have prepared the three-dimensional structure for AdeC using MODELLER v9.16 and identified its active binding site using SiteMap. Using high-throughput virtual screening, we identified compounds from a large library of biogenic compounds on the basis of their effective interaction at the binding site of AdeC. The validation of docking step was performed by plotting ROC curve (enrichment calculations). The docked complexes were further analyzed for their binding free energies by molecular mechanics using Generalized Born model and Solvent Accessibility (MMGBSA). The molecular dynamics simulation was performed for AdeC-ZINC77257599 complex using GROMACS. The present rational drug designing, molecular mechanics and molecular dynamics data provided an inhibitor, i.e, ZINC77257599 [(3R,4Z,6E,8E)-3-hydroxy-2,2,4-trimethyl-10-oxazol-5-yl-deca-4,6,8-trienamide], for the outer membrane protein component (AdeC) of efflux pump AdeABC of A. baumannii.

Subtractive proteomics to identify novel drug targets and reverse vaccinology for the development of chimeric vaccine against Acinetobacter baumannii

The emergence of drug-resistant Acinetobacter baumannii is the global health problem associated with high mortality and morbidity. Therefore it is high time to find a suitable therapeutics for this pathogen. In the present study, subtractive proteomics along with reverse vaccinology approaches were used to predict suitable therapeutics against A. baumannii. Using subtractive proteomics, we have identified promiscuous antigenic membrane proteins that contain the virulence factors, resistance factors and essentiality factor for this pathogenic bacteria. Selected promiscuous targeted membrane proteins were used for the design of chimeric-subunit vaccine with the help of reverse vaccinology. Available best tools and servers were used for the identification of MHC class I, II and B cell epitopes. All selected epitopes were further shortlisted computationally to know their immunogenicity, antigenicity, allergenicity, conservancy and toxicity potentials. Immunogenic predicted promiscuous peptides used for the development of chimeric subunit vaccine with immune-modulating adjuvants, linkers, and PADRE (Pan HLA-DR epitopes) amino acid sequence. Designed vaccine construct V4 also interact with the MHC, and TLR4/MD2 complex as confirm by docking and molecular dynamics simulation studies. Therefore designed vaccine construct V4 can be developed to control the host-pathogen interaction or infection caused by A. baumannii.

Mechanism of Anti-bacterial Activity of Zinc Oxide Nanoparticle Against Carbapenem-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a multi-drug resistant opportunistic pathogen, which causes respiratory and urinary tract infections. Its prevalence increases gradually in the clinical setup. Carbapenems (beta-lactam) are most effective antibiotics till now against A. baumannii, but the development of resistance against it may lead to high mortality. Therefore, it is of utmost importance to develop an alternative drug against A. baumannii. In the present study, we have synthesized ZnO nanoparticle (ZnO-NP) and characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and UV-Visible spectroscopy. Prepared ZnO-NPs have the size of 30 nm and have different characteristics of ZnO-NPs. Growth kinetics and disk diffusion assay showed that ZnO-NP demonstrated good antibacterial activity against carbapenem resistant A. baumannii. We have also investigated the mechanism of action of ZnO-NPs on the carbapenem resistant strain of A. baumannii. The proposed mechanism of action of ZnO involves the production of reactive oxygen species, which elevates membrane lipid peroxidation that causes membrane leakage of reducing sugars, DNA, proteins, and reduces cell viability. These results demonstrate that ZnO-NP could be developed as alternative therapeutics against A. baumannii.

Inhibitory effect of α-mangostin on Acinetobacter baumannii biofilms - an in vitro study

The present study was designed to investigate the anti-biofilm potential of alpha-mangostin (α-MG) against Acinetobacter baumannii (AB). The biofilm inhibitory concentration (BIC) of α-MG against AB was found to be 2 μg ml^-1. α-MG (0.5, 1 and 2 μg ml^-1) exhibited non-bactericidal concentration-dependent anti-biofilm activities against AB. However, α-MG failed to disintegrate the mature biofilms of AB even at a 10-fold increased concentration from its BIC. Results from qRT-PCR and in vitro bioassays further demonstrated that α-MG downregulated the expression of bfmR, pgaA, pgaC, csuA/B, ompA, bap, katE, and sodB genes, which correspondingly affects biofilm formation and its associated virulence traits. The present study suggests that α-MG exerts its anti-biofilm property by interrupting initial biofilm formation and the cell-to-cell signaling mechanism of AB. Additional studies are required to understand the mode of action responsible for the anti-biofilm property.

Novel Polymyxin Combination With Antineoplastic Mitotane Improved the Bacterial Killing Against Polymyxin-Resistant Multidrug-Resistant Gram-Negative Pathogens

Due to limited new antibiotics, polymyxins are increasingly used to treat multidrug-resistant (MDR) Gram-negative bacteria, in particular carbapenem-resistant Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Unfortunately, polymyxin monotherapy has led to the emergence of resistance. Polymyxin combination therapy has been demonstrated to improve bacterial killing and prevent the emergence of resistance. From a preliminary screening of an FDA drug library, we identified antineoplastic mitotane as a potential candidate for combination therapy with polymyxin B against polymyxin-resistant Gram-negative bacteria. Here, we demonstrated that the combination of polymyxin B with mitotane enhances the in vitro antimicrobial activity of polymyxin B against 10 strains of A. baumannii, P. aeruginosa, and K. pneumoniae, including polymyxin-resistant MDR clinical isolates. Time-kill studies showed that the combination of polymyxin B (2 mg/L) and mitotane (4 mg/L) provided superior bacterial killing against all strains during the first 6 h of treatment, compared to monotherapies, and prevented regrowth and emergence of polymyxin resistance in the polymyxin-susceptible isolates. Electron microscopy imaging revealed that the combination potentially affected cell division in A. baumannii. The enhanced antimicrobial activity of the combination was confirmed in a mouse burn infection model against a polymyxin-resistant A. baumannii isolate. As mitotane is hydrophobic, it was very likely that the synergistic killing of the combination resulted from that polymyxin B permeabilized the outer membrane of the Gram-negative bacteria and allowed mitotane to enter bacterial cells and exert its antimicrobial effect. These results have important implications for repositioning non-antibiotic drugs for antimicrobial purposes, which may expedite the discovery of novel therapies to combat the rapid emergence of antibiotic resistance.

Rationale and design of an inhibitor of RecA protein as an inhibitor of Acinetobacter baumannii

Acinetobacter baumannii is one of the ESKAPE pathogen, which causes pneumonia, urinary tract infections, and is linked to high degree of morbidity and mortality. One-way antibiotic and disinfectant resistance is acquired by the activation of RecA-mediated DNA repair (SOS-response) that maintain ROS-dependent DNA damage caused by these anti-bacterial molecules. To increase the efficacy of different anti-microbial, there is a need to design an inhibitor against RecA of A. baumannii. We have performed homology modeling to generate the structure of RecA, followed by model refinement and validation. High-throughput virtual screening of 1,80,313 primary and secondary metabolites against RecA was performed in HTVS, SP, and XP docking modes. The selected 195 compounds were further analyzed for binding free energy by molecular mechanics approach. The selected top two molecules from molecular mechanics approach were further validated by molecular dynamics simulation (MDS). In-silico high-throughput virtual screening and MDS validation identified ZINC01530654 or  (+-)-2-((4-((7-Chloro-4-quinolyl)amino)pentyl)ethylamino)ethanol sulfate (or hydroxychloroquine sulfate) as a possible lead molecule binding to RecA protein. We have experimentally determined the mechanism of ZINC01530654 to RecA protein. These findings suggest a strategy to chemically inhibit the vital process controlled by RecA that could be helpful for the development of new antibacterial agents.

In-silico screening and experimental validation reveal L-Adrenaline as anti-biofilm molecule against biofilm-associated protein (Bap) producing Acinetobacter baumannii

Acinetobacter baumannii, an ESKAPE pathogen, causes various nosocomial infections and has capacity to produce biofilm. Biofilm produced by this bacterium is highly tolerant to environmental factors and different antibiotics. Biofilm-associated protein (Bap) plays a significant role in the biofilm formation by A. baumannii and found in the extra cellular matrix of the biofilm. Therefore, it becomes essential to find a potential drug against Bap that has capacity to inhibit biofilm formation by A. baumannii. In-silico screening, molecular mechanics and molecular dynamics studies identified ZINC00039089 (L-Adrenaline) as an inhibitor for Bap of A. baumannii. Recently, it is reported that Bap can form amyloid like structure; hence we have created dimer of Bap protein. This inhibitor can bind to dimeric Bap with good affinity. It confirms that ZINC00039089 (L-Adrenaline) can bind with Bap monomer as well as oligomeric Bap, responsible for amyloid formation and biofilm formation. Hence, we have tested Adrenaline as an anti-biofilm molecule and determined its IC₅₀ value against biofilm. The result showed Adrenaline has anti-biofilm activity with IC₅₀ value of 75μg/ml. Therefore; our finding suggests that L-Adrenaline can be developed to inhibit biofilm formation by carbapenem resistant strain of Acinetobacter baumannii.

Polyvinylpyrrolidone-Capped Silver Nanoparticle Inhibits Infection of Carbapenem-Resistant Strain of Acinetobacter baumannii in the Human Pulmonary Epithelial Cell

Acinetobacter baumannii, an opportunistic ESKAPE pathogen, causes respiratory and urinary tract infections. Its prevalence increases gradually in the clinical setup. Pathogenicity of Acinetobacter is significantly influenced by its ability to infect and survive in human pulmonary cells. Therefore, it is important to study the infection of A. baumannii in human pulmonary host cell (A-549), monitoring surface interacting and internalized bacteria. It was found that during infection of A. baumannii, about 40% bacteria adhered to A-549, whereas 20% got internalized inside pulmonary cell and induces threefold increase in the reactive oxygen species production. We have synthesized polyvinylpyrrolidone (PVP)-capped AgNPs using chemical methods and tested its efficacy against carbapenem-resistant strain of A. baumannii. PVP-capped silver nanoparticles (PVP-AgNPs) (30 µM) have shown antibacterial activity against carbapenem-resistant strain of A. baumannii and this concentration does not have any cytotoxic effect on the human pulmonary cell line (IC₅₀ is 130 µM). Similarly, PVP-AgNPs treatment decreases 80% viability of intracellular bacteria, decreases adherence of A. baumannii to A-549 (40 to 2.2%), and decreases intracellular concentration (20 to 1.3%) of A. baumannii. This concludes that PVP-AgNPs can be developed as a substitute for carbapenem to control the infection caused by carbapenem-resistant A. baumannii.

Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii in Greece: an extended review (2000–2015)

Carbapenem-resistant Acinetobacter baumannii (CRAB) is endemic in Greece. CRAB initially emerged in 2000 and since then, carbapenemases still have a crucial role in CRAB appearance, except for a few cases resulting from efflux pump or outer-membrane protein mechanisms. OXA-type carbapenemases present the highest prevalence worldwide and bla OXA-23-like and bla OXA-58-like are the most important genes found; VIM-yielding CRAB have also been detected, while a single CRAB isolate producing NDM has quite recently emerged in Greece. The predominant OXA-23 producers are associated with multilocus sequence typing Pasteur scheme sequence type 2 clonal strains of the international clone II. The emergence of colistin-resistant CRAB has complicated the treatment of such infections and the interpretation of susceptibility data. Infection control measures and adjusted antimicrobial treatment strategies could confine CRAB spread. The aim of this review is to go through the molecular epidemiology of CRAB, in an endemic area and highlight its potential future evolution.

In silico high-throughput virtual screening and molecular dynamics simulation study to identify inhibitor for AdeABC efflux pump of Acinetobacter baumannii

Emergence of multi-drug resistant strains of Acinetobacter baumannii has caused significant health problems and is responsible for high morbidity and mortality. Overexpression of AdeABC efflux system is one of the major mechanisms. In this study, we have focused on overcoming the drug resistance by identifying inhibitors that can effectively bind and inhibit integral membrane protein, AdeB of this efflux pump. We performed homology modeling to generate structure of AdeB using MODELLER v9.16 followed by model refinement using 3D-Refine tool and validated using PSVS, ProsaWeb, ERRAT, etc. The energy minimization of modeled protein was done using Protein preparation wizard application included in Schrodinger suite. High-throughput virtual screening of 159,868 medicinal compounds against AdeB was performed using three sequential docking modes (i.e. HTVS, SP and XP). Furthermore, absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis was done using QIKPROP. The selected 123 compounds were further analyzed for binding free energy by molecular mechanics (using prime MM-GBSA). We have also performed enrichment study (ROC curve analysis) to validate our docking results. The selected molecule and its interaction with AdeB were validated by molecular dynamics simulation (MDS) using GROMACS v5.1.4. In silico high-throughput virtual screening and MDS validation identified ZINC01155930 ((4R)-3-(cycloheptoxycarbonyl)-4-(4-etochromen-3-yl)-2-methyl-4,6,7,8-tetrahydroquinolin-5-olate) as a possible inhibitor for AdeB. Hence, it might be a suitable efflux pump inhibitor worthy of further investigation in order to be used for controlling infections caused by Acinetobacter baumannii.

A Mechanism of Synergistic Effect of Streptomycin and Cefotaxime on CTX-M-15 Type β-lactamase Producing Strain of E. cloacae: A First Report

A bla_CTX-M-15 gene is one of the most prevalent resistant marker found in member of enterobacteriaceae. It encodes cefotaxime hydrolysing β-lactamase-15 (CTX-M-15) causing resistance against beta lactam antibiotics. Since single antibiotic therapy fails to control infection caused by multidrug resistance strain, therefore combination therapy was came into practice as an effective treatment. We have first time explained the mechanism where two antibiotics of different classes work against resistant strains. Binding parameters obtained by spectroscopic approach showed significant interaction and complex formation between drugs and CTX-M-15 enzyme with decreased k_sv and k_q values. CD analysis showed altered conformation and significant changes in alpha helical content of CTX-M-15 enzyme on interaction with streptomycin in combination with cephalosporin. Steady state kinetics revealed decrease in hydrolytic efficiency of enzyme to about 27% by cooperative binding behavior upon sequential treatment of enzyme with streptomycin and cefotaxime. Therefore, the study concludes that combination therapy against CTX-M-15 producing strain with Cefotaxime/Streptomycin in 1:10 molar ratio, decreases CTX-M-15 efficiency significantly because of the fact that streptomycin induced structural changes in CTX-M-15 hence cefotaxime was not properly bound on its active site for hydrolysis rather available for the target to inhibit bacterial cells.

OXA β-lactamases

The OXA β-lactamases were among the earliest β-lactamases detected; however, these molecular class D β-lactamases were originally relatively rare and always plasmid mediated. They had a substrate profile limited to the penicillins, but some became able to confer resistance to cephalosporins. From the 1980s onwards, isolates of Acinetobacter baumannii that were resistant to the carbapenems emerged, manifested by plasmid-encoded β-lactamases (OXA-23, OXA-40, and OXA-58) categorized as OXA enzymes because of their sequence similarity to earlier OXA β-lactamases. It was soon found that every A. baumannii strain possessed a chromosomally encoded OXA β-lactamase (OXA-51-like), some of which could confer resistance to carbapenems when the genetic environment around the gene promoted its expression. Similarly, Acinetobacter species closely related to A. baumannii also possessed their own chromosomally encoded OXA β-lactamases; some could be transferred to A. baumannii, and they formed the basis of transferable carbapenem resistance in this species. In some cases, the carbapenem-resistant OXA β-lactamases (OXA-48) have migrated into the Enterobacteriaceae and are becoming a significant cause of carbapenem resistance. The emergence of OXA enzymes that can confer resistance to carbapenems, particularly in A. baumannii, has transformed these β-lactamases from a minor hindrance into a major problem set to demote the clinical efficacy of the carbapenems.

Allosteric site-mediated active site inhibition of PBP2a using Quercetin 3-O-rutinoside and its combination

Recent crystallographic study revealed the involvement of allosteric site in active site inhibition of penicillin binding protein (PBP2a), where one molecule of Ceftaroline (Cef) binds to the allosteric site of PBP2a and paved way for the other molecule (Cef) to bind at the active site. Though Cef has the potency to inhibit the PBP2a, its adverse side effects are of major concern. Previous studies have reported the antibacterial property of Quercetin derivatives, a group of natural compounds. Hence, the present study aims to evaluate the effect of Quercetin 3-o-rutinoside (Rut) in allosteric site-mediated active site inhibition of PBP2a. The molecular docking studies between allosteric site and ligands (Rut, Que, and Cef) revealed a better binding efficiency (G-score) of Rut (-7.790318) and Cef (-6.194946) with respect to Que (-5.079284). Molecular dynamic (MD) simulation studies showed significant changes at the active site in the presence of ligands (Rut and Cef) at allosteric site. Four different combinations of Rut and Cef were docked and their G-scores ranged between -6.320 and -8.623. MD studies revealed the stability of the key residue (Ser403) with Rut being at both sites, compared to other complexes. Morphological analysis through electron microscopy confirmed that combination of Rut and Cefixime was able to disturb the bacterial cell membrane in a similar fashion to that of Rut and Cefixime alone. The results of this study indicate that the affinity of Rut at both sites were equally good, with further validations Rut could be considered as an alternative for inhibiting MRSA growth.

Complete Nucleotide Sequence of pGA45, a 140,698-bp IncFIIY Plasmid Encoding bla IMI-3-Mediated Carbapenem Resistance, from River Sediment

Plasmid pGA45 was isolated from the sediments of Haihe River using Escherichia coli CV601 (gfp-tagged) as recipients and indigenous bacteria from sediment as donors. This plasmid confers reduced susceptibility to imipenem which belongs to carbapenem group. Plasmid pGA45 was fully sequenced on an Illumina HiSeq 2000 sequencing system. The complete sequence of plasmid pGA45 was 140,698 bp in length with an average G + C content of 52.03%. Sequence analysis shows that pGA45 belongs to IncFII_Y group and harbors a backbone region which shares high homology and gene synteny to several other IncF plasmids including pNDM1_EC14653, pYDC644, pNDM-Ec1GN574, pRJF866, pKOX_NDM1, and pP10164-NDM. In addition to the backbone region, plasmid pGA45 harbors two notable features including one bla_IMI-3-containing region and one type VI secretion system region. The bla_IMI-3-containing region is responsible for bacteria carbapenem resistance and the type VI secretion system region is probably involved in bacteria virulence, respectively. Plasmid pGA45 represents the first complete nucleotide sequence of the bla_IMI-harboring plasmid from environment sample and the sequencing of this plasmid provided insight into the architecture used for the dissemination of bla_IMI carbapenemase genes.

Screening of Herbal-Based Bioactive Extract Against Carbapenem-Resistant Strain of Acinetobacter baumannii

Acinetobacter baumannii is grouped in the ESKAPE pathogens by Infectious Disease Society of America, which is linked to high degree of morbidity, mortality, and increased costs. The high level of acquired and intrinsic resistance mechanisms of these bacteria makes it an urgent requirement to find a suitable alternative to carbapenem, a commonly prescribed drug for Acinetobacter infection. In this study, methanolic extracts of six medicinal plants were subjected to phytochemical screening and their antimicrobial activity was tested against two strains of A. baumannii (ATCC 19606, carbapenem-sensitive strain, and RS 307, carbapenem-resistant strain). Synergistic effect of the plant extracts and antibiotics was also tested. Bael or Aegle marmelos contains tannin, phenol, terpenoids, glycoside, alkaloids, coumarine, steroid, and quinones. Flowers of madar or Calotropis procera possess tannin, phenol, terpenoids, glycoside, quinone, anthraquinone, anthocyanin, coumarin, and steroid. An inhibitory growth curve was seen for both the bacterial strains when treated with A. marmelos, Curcuma longa, and leaves and flowers of C. procera. Antibiotics alone showed a small zone of inhibition, but when used with herbal extracts they exhibited larger zone of inhibition. Synergistic effect of A. marmelos and imipenem was the best against both the strains of A. baumannii. From this study, it can be concluded that extracts from A. marmelos and leaves and flowers of C. procera exhibited the most effective antibacterial activity. These herbal extracts may be used to screen the bioactive compound against the carbapenem-resistant strain of A. baumannii.

Rapid detection of Acinetobacter baumannii and molecular epidemiology of carbapenem-resistant A. baumannii in two comprehensive hospitals of Beijing, China

Acinetobacter baumannii is an important opportunistic pathogen associated with a variety of nosocomial infections. A rapid and sensitive molecular detection in clinical isolates is quite needed for the appropriate therapy and outbreak control of A. baumannii. Group 2 carbapenems have been considered the agents of choice for the treatment of multiple drug-resistant A. baumannii. But the prevalence of carbapenem-resistant A. baumannii (CRAB) has been steadily increasing in recent years. Here, we developed a loop-mediated isothermal amplification (LAMP) assay for the rapid detection of A. baumannii in clinical samples by using high-specificity primers of the bla OXA-51 gene. Then we investigated the OXA-carbapenemases molecular epidemiology of A. baumannii isolates in two comprehensive hospitals in Beijing. The results showed that the LAMP assay could detect target DNA within 60 min at 65°C. The detection limit was 50 pg/μl, which was about 10-fold greater than that of PCR. Furthermore, this method could distinguish A. baumannii from the homologous A. nosocomialis and A. pittii. A total of 228 positive isolates were identified by this LAMP-based method for A. baumannii from 335 intensive care unit patients with clinically suspected multi-resistant infections in two hospitals in Beijing. The rates of CRAB are on the rise and are slowly becoming a routine phenotype for A. baumannii. Among the CRABs, 92.3% harbored both the bla OXA-23 and bla OXA-51 genes. Thirty-three pulsotypes were identified by pulsed-field gel electrophoresis, and the majority belonged to clone C. In conclusion, the LAMP method developed for detecting A. baumannii was faster and simpler than conventional PCR and has great potential for both point-of-care testing and basic research. We further demonstrated a high distribution of class D carbapenemase-encoding genes, mainly OXA-23, which presents an emerging threat in hospitals in China.

Characterization of carbapenem-resistant Acinetobacter baumannii isolates in a Chinese teaching hospital

Carbapenem-resistant Acinetobacter baumannii (CRAB) presents a serious therapeutic and infection control challenge. In this study, we investigated the epidemiological and molecular differences of CRAB and the threatening factors for contributing to increased CRAB infections at a hospital in western China. A total of 110 clinical isolates of A. baumannii, collected in a recent 2-year period, were tested for carbapenem antibiotic susceptibility, followed by a molecular analysis of carbapenemase genes. Genetic relatedness of the isolates was characterized by multilocus sequence typing. Sixty-seven of the 110 isolates (60.9%) were resistant to carbapenems, 80.60% (54/67) of which carried the bla_OXA-23 gene. Most of these CRAB isolates (77.62%) were classified as clone complex 92 (CC92), and sequence type (ST) 92 was the most prevalent STs, followed by ST195, ST136, ST843, and ST75. One CRAB isolate of ST195 harbored plasmid pAB52 from a Chinese patient without travel history. This plasmid contains toxin–antitoxin elements related to adaptation for growth, which might have emerged as a common vehicle indirectly mediating the spread of OXA-23 in CRAB. Thus, CC92 A. baumannii carrying OXA-23 is a major drug-resistant strain spreading in China. Our findings indicate that rational application of antibiotics is indispensable for minimizing widespread of drug resistance.

Antimicrobial active herbal compounds against Acinetobacter baumannii and other pathogens

Bacterial pathogens cause a number of lethal diseases. Opportunistic bacterial pathogens grouped into ESKAPE pathogens that are linked to the high degree of morbidity, mortality and increased costs as described by Infectious Disease Society of America. Acinetobacter baumannii is one of the ESKAPE pathogens which cause respiratory infection, pneumonia and urinary tract infections. The prevalence of this pathogen increases gradually in the clinical setup where it can grow on artificial surfaces, utilize ethanol as a carbon source and resists desiccation. Carbapenems, a β-lactam, are the most commonly prescribed drugs against A. baumannii. The high level of acquired and intrinsic carbapenem resistance mechanisms acquired by these bacteria makes their eradication difficult. The pharmaceutical industry has no solution to this problem. Hence, it is an urgent requirement to find a suitable alternative to carbapenem, a commonly prescribed drug for Acinetobacter infection. In order to do this, here we have made an effort to review the active compounds of plants that have potent antibacterial activity against many bacteria including carbapenem resistant strain of A. baumannii. We have also briefly highlighted the separation and identification methods used for these active compounds. This review will help researchers involved in the screening of herbal active compounds that might act as a replacement for carbapenem.

Contribution of Acinetobacter-derived cephalosporinase-30 to sulbactam resistance in Acinetobacter baumannii

The sulbactam resistance rate in Acinetobacter baumannii has increased worldwide. Previous reports have shown that the β-lactamase bla_TEM-1 confers resistance to sulbactam in A. baumannii. The purpose of this study was to examine whether other β-lactamases, including the Acinetobacter-derived cephalosporinase (ADC), OXA-23, OXA-24/72, and OXA-58 families, also contribute to sulbactam resistance in A. baumannii. The correlation between these β-lactamases and the sulbactam minimal inhibitory concentration (MIC) was determined using A. baumannii clinical isolates from diverse clonality, which were collected in a nationwide surveillance program from 2002 to 2010 in Taiwan. A possible association between the genetic structure of ISAba1-bla_ADC-30 and sulbactam resistance was observed because this genetic structure was detected in 97% of sulbactam-resistant strains compared with 10% of sulbactam-susceptible strains. Transformation of ISAba1-bla_ADC-30 into susceptible strains increased the sulbactam MIC from 2 to 32 μg/ml, which required bla_ADC-30 overexpression using an upstream promoter in ISAba1. Flow cytometry showed that ADC-30 production increased in response to sulbactam, ticarcillin, and ceftazidime treatment. This effect was regulated at the RNA level but not by an increase in the bla_ADC-30 gene copy number as indicated by quantitative PCR. Purified ADC-30 decreased the inhibitory zone created by sulbactam or ceftazidime, similarly to TEM-1. In conclusion, ADC-30 overexpression conferred resistance to sulbactam in diverse clinical A. baumannii isolates.

Quantitative proteomics to study carbapenem resistance in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen causing pneumonia, respiratory infections and urinary tract infections. The prevalence of this lethal pathogen increases gradually in the clinical setup where it can grow on artificial surfaces, utilize ethanol as a carbon source. Moreover it resists desiccation. Carbapenems, a β-lactam, are the most commonly prescribed drugs against A. baumannii. Resistance against carbapenem has emerged in Acinetobacter baumannii which can create significant health problems and is responsible for high morbidity and mortality. With the development of quantitative proteomics, a considerable progress has been made in the study of carbapenem resistance of Acinetobacter baumannii. Recent updates showed that quantitative proteomics has now emerged as an important tool to understand the carbapenem resistance mechanism in Acinetobacter baumannii. Present review also highlights the complementary nature of different quantitative proteomic methods used to study carbapenem resistance and suggests to combine multiple proteomic methods for understanding the response to antibiotics by Acinetobacter baumannii.

Phosphoproteomics as an emerging weapon to develop new antibiotics against carbapenem resistant strain of Acinetobacter baumannii

Acinetobacter baumannii causes pneumonia, bloodstream infections, urinary tract infections, respiratory infections and meningitis. A. baumannii has developed resistance against most of the antibiotics including carbapenem. Therefore, to battle carbapenem resistance, there is a need to develop antimicrobial drugs with new modes of action. Phosphoproteomics will help identify the differentially phosphorylated protein and its crucial phosphosites which facilitate the elucidation of molecular mechanism of signaling and regulation of carbapenem resistant strain of A. baumannii as compared to carbapenem sensitive strain. This understanding might be useful for the development of new antibiotics against kinases involved in the phosphorylation of identified phosphosites in carbapenem resistant strain of A. baumannii. The proposed antibiotics selectively inhibit carbapenem resistant strain which further avoids its excessive use against carbapenem sensitive strain and thereafter reduces emergence of resistance.