Human Pleural Fluid Elicits Pyruvate and Phenylalanine Metabolism in Acinetobacter baumannii to Enhance Cytotoxicity and Immune Evasion

The CCAAT box-harboring proteins represent a family of heterotrimeric transcription factors which is highly conserved in eukaryotes. In fungi, one of the particularly important homologs of this family is the Hap complex that separates the DNA-binding domain from the activation domain and imposes essential impacts on regulation of a wide range of cellular functions. So far, a comprehensive summary of this complex has been described in filamentous fungi but not in the yeast. In this review, we summarize a number of studies related to the structure and assembly mode of the Hap complex in a list of representative yeasts. Furthermore, we emphasize recent advances in understanding the regulatory functions of this complex, with a special focus on its role in regulating respiration, production of reactive oxygen species (ROS) and iron homeostasis.Fil: Nyah, Rodman. California State University; Estados UnidosFil: Martinez, Jasmine. California State University; Estados UnidosFil: Fung, Sammie. California State University; Estados UnidosFil: Nakanouchi, Jun. California State University; Estados UnidosFil: Myers, Amber L.. California State University; Estados UnidosFil: Harris, Caitlin M.. California State University; Estados UnidosFil: Dang, Emily. California State University; Estados UnidosFil: Fernandez, Jennifer. California State University; Estados UnidosFil: Liu, Christine. California State University; Estados UnidosFil: Mendoza, Anthony M.. California State University; Estados UnidosFil: Jimenez, Verónica. California State University; Estados UnidosFil: Nikolaidis, Nikolas. California State University; Estados UnidosFil: Brennan, Catherine A.. California State University; Estados UnidosFil: Bonomo, Robert A.. Louis Stokes Cleveland Department of Veterans Affairs Medical Cente; Estados Unidos. Center for Antimicrobial Resistance and Epidemiology; Estados Unidos. Case Western Reserve University School of Medicine; Estados UnidosFil: Sieira, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Ramirez, Maria Soledad. California State University; Estados Unido

Acinetobacter baumannii. An ancient commensal with weapons of a pathogen

Acinetobacter baumannii is regarded as a life-threatening pathogen associated with community-acquired and nosocomial infections, mainly pneumonia. The rise in the number of A. baumannii antibiotic-resistant strains reduces effective therapies and increases mortality. Bacterial comparative genomic studies have unraveled the innate and acquired virulence factors of A. baumannii. These virulence factors are involved in antibiotic resistance, environmental persistence, host-pathogen interactions, and immune evasion. Studies on host–pathogen interactions revealed that A. baumannii evolved different mechanisms to adhere to in order to invade host respiratory cells as well as evade the host immune system. In this review, we discuss current data on A. baumannii genetic features and virulence factors. An emphasis is given to the players in host–pathogen interaction in the respiratory tract. In addition, we report recent investigations into host defense systems using in vitro and in vivo models, providing new insights into the innate immune response to A. baumannii infections. Increasing our knowledge of A. baumannii pathogenesis may help the development of novel therapeutic strategies based on anti-adhesive, anti-virulence, and anti-cell to cell signaling pathways drugs

H-NS plays a role in expression of Acinetobacter baumannii virulence features

Acinetobacter baumannii has become a major problem in the clinical setting with the prevalence of infections caused by multidrug-resistant strains on the increase. Nevertheless, only a limited number of molecular mechanisms involved in the success of A. baumannii as a human pathogen have been described. In this study, we examined the virulence features of a hypermotile derivative of A. baumannii strain ATCC 17978, which was found to display enhanced adherence to human pneumocytes and elevated levels of lethality toward Caenorhabditis elegans nematodes. Analysis of cellular lipids revealed modifications to the fatty acid composition, providing a possible explanation for the observed changes in hydrophobicity and subsequent alteration in adherence and motility. Comparison of the genome sequences of the hypermotile variant and parental strain revealed that an insertion sequence had disrupted an hns-like gene in the variant. This gene encodes a homologue of the histone-like nucleoid structuring (H-NS) protein, a known global transcriptional repressor. Transcriptome analysis identified the global effects of this mutation on gene expression, with major changes seen in the autotransporter Ata, a type VI secretion system, and a type I pilus cluster. Interestingly, isolation and analysis of a second independent hypermotile ATCC 17978 variant revealed a mutation to a residue within the DNA binding region of H-NS. Taken together, these mutants indicate that the phenotypic and transcriptomic differences seen are due to loss of regulatory control effected by H-NS.This work was supported by project grant 535053 to M.H.B. and I.T.P. from the National Health and Medical Research Council, Australia. B.A.E. is the recipient of a School of Biological Sciences Endeavor International Postgraduate Research Scholarship, and K.A.H. is supported by an APD fellowship from the Australian Research Council (DP110102680)

Pathogenic Acinetobacter: From the cell surface to infinity and beyond

The genus Acinetobacter encompasses multiple nosocomial opportunistic pathogens that are of increasing worldwide relevance because of their ability to survive exposure to various antimicrobial and sterilization agents. Among these, Acinetobacter baumannii, Acinetobacter nosocomialis, and Acinetobacter pittii are the most frequently isolated in hospitals around the world. Despite the growing incidence of multidrug-resistant Acinetobacter spp., little is known about the factors that contribute to pathogenesis. New strategies for treating and managing infections caused by multidrug-resistant Acinetobacter strains are urgently needed, and this requires a detailed understanding of the pathobiology of these organisms. In recent years, some virulence factors important for Acinetobacter colonization have started to emerge. In this review, we focus on several recently described virulence factors that act at the bacterial surface level, such as the capsule, O-linked protein glycosylation, and adhesins. Furthermore, we describe the current knowledge regarding the type II and type VI secretion systems present in these strains

Lysin Based Antimicrobial Peptides Against Acinetobacter Baumannii

Acinetobacter baumannii is a Gram-negative bacterial pathogen responsible for a range of nosocomial infections. The recent rise and spread of multidrug resistant A. baumannii clones has fueled a search for alternative therapies, including bacteriophage endolysins with potent antibacterial activities. A common feature of these lysins is the presence of a highly positively charged C-terminal domain with a likely role in promoting outer membrane penetration. In the current study, we show that the C-terminal amino acids 108-138 of phage lysin PlyF307, named P307, alone was sufficient to kill A. baumannii (\u3e3-logs). Furthermore, P307 could be engineered for improved activity, the most active derivative being P307SQ-8C (\u3e5-log kill). Both P307 and P307SQ-8C showed high in vitro activity against A. baumannii in biofilms. Moreover, P307SQ-8C exhibited MICs comparable to levofloxacin and ceftazidime and acted synergistically with polymyxin B. While the peptides were shown to kill by disrupting the bacterial cytoplasmic membrane, they did not lyse human red blood cells or B cells; however, serum was found to be inhibitory to lytic activity. In a murine model of A. baumannii skin infection, P307SQ-8C reduced the bacterial burden by ~2-logs in 2 h. This study demonstrates the prospect of using peptide derivatives from bacteriophage lysins to treat topical infections and remove biofilms caused by Gram-negative pathogens

Insights into Acinetobacter baumannii: A review of microbiological, virulence, and resistance traits in a threatening nosocomial pathogen

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Being a multidrug-resistant and an invasive pathogen, Acinetobacter baumannii is one of the major causes of nosocomial infections in the current healthcare system. It has been recognized as an agent of pneumonia, septicemia, meningitis, urinary tract and wound infections, and is associated with high mortality. Pathogenesis in A. baumannii infections is an outcome of multiple virulence factors, including porins, capsules, and cell wall lipopolysaccharide, enzymes, biofilm production, motility, and iron-acquisition systems, among others. Such virulence factors help the organism to resist stressful environmental conditions and enable development of severe infections. Parallel to increased prevalence of infections caused by A. baumannii, challenging and diverse resistance mechanisms in this pathogen are well recognized, with major classes of antibiotics becoming minimally effective. Through a wide array of antibiotic-hydrolyzing enzymes, efflux pump changes, impermeability, and antibiotic target mutations, A. baumannii models a unique ability to maintain a multidrug-resistant phenotype, further complicating treatment. Understanding mechanisms behind diseases, virulence, and resistance acquisition are central to infectious disease knowledge about A. baumannii. The aims of this review are to highlight infections and disease-producing factors in A. baumannii and to touch base on mechanisms of resistance to various antibiotic classes

Estudio de mecanismos de tolerancia, persistencia y resistencia en patógenos nosocomiales: Búsqueda de nuevas dianas terapéuticas

Programa Oficial de Doctorado en Ciencias de la Salud. 5007V01[Resumen] Una de las mayores amenazas para la salud pública es el incremento de bacterias resistentes a los antimicrobianos. Dicho incremento se debe a múltiples factores, entre los que comienzan a destacar la existencia de poblaciones bacterianas tolerantes y/o persistentes a las condiciones de estrés, incluyendo el tratamiento antimicrobiano. A lo largo de la presente tesis doctoral se han analizado diversos mecanismos moleculares de persistencia y/o tolerancia bacteriana, destacando la red del quorum (sensing/quenching) y los sistemas toxina-antitoxina (TA) en aislamientos ambientales y clínicos. En relación con la red del quorum, llevamos a cabo estudios genómicos y de expresión ante condiciones de estrés en la cepa aislada de ambiente hospitalario aéreo Acinetobacter sp. 5-2AC02 (cercano a la especie A. towneri) destacando el cluster del metabolismo de la acetoína y caracterizando el regulador negativo, AcoN. Posteriormente, estudiamos la importancia de dicha red del quorum en el desarrollo de bacteriemia secundaria a neumonía en aislamientos clínicos de Acinetobacter baumannii. Finalmente, se realizaron estudios de caracterización funcional y análisis bacteriano de los sistemas toxina-antitoxina (TA) (como el módulo AbkB/AbkA y otros) en aislamientos de A. baumannii y Escherichia coli.[Resumo] Unha das maiores ameazas para a saúde pública é o incremento de bacterias resistentes aos antimicrobianos. Devandito incremento débese a múltiples factores, entre os que comezan a destacar a existencia de poboacións bacterianas tolerantes e/ou persistentes ás condicións de estrés, incluíndo o tratamento antimicrobiano. Ao longo da presente tese doutoral analizáronse diversos mecanismos moleculares de persistencia e/ou tolerancia bacteriana, destacando a rede do quorum (sensing/quenching) e os sistemas toxina-antitoxina (TA) en illamentos ambientais e clínicos. En relación coa rede do Quorum, levamos a cabo estudos xenómicos e de expresión ante condicións de estrés na cepa illada de ambiente hospitalario aéreo Acinetobacter sp. 5-2AC02 (próximo á especie A. towneri) destacando o clúster do metabolismo da acetoína e caracterizando o regulador negativo, AcoN. Posteriormente, estudamos a importancia da devandita rede do quorum no desenvolvemento de bacteriemia secundaria a pneumonía en illamentos clínicos de Acinetobacter baumannii. Finalmente, realizáronse estudos de caracterización funcional e análise bacteriano dos sistemas toxina-antitoxina (TA) (como o módulo AbkB/AbkA e outros) en illamentos de A. baumannii e Escherichia coli.[Abstract] One of the greatest current threats to public health is the rapid increase in the emergence of antibiotic resistant strains of bacteria. This increase is due to multiple factors, including the development of tolerant and/or persistent populations under stress conditions (e.g. antimicrobial treatment). The present thesis reports research investigating several molecular mechanisms of bacterial persistence and/or tolerance, particularly the quorum network (sensing/quenching) and toxin-antitoxin systems (TA), in both clinical and environmental isolates. In relation to the quorum network, we carried out genomic and expression studies with an airborne strain isolated from a hospital environment, Acinetobacter sp. 5- 2AC02 (closely related to A. towneri), and subjected to different stress conditions. We identified the acetoin metabolism cluster and characterized the negative regulator, AcoN protein. We then investigated the importance of the quorum network in clinical isolates of Acinetobacter baumannii in the development of secondary bacteraemia following pneumonia. Finally, we carried out functional characterization studies and examined toxinantitoxin (TA) systems (such as AbkB/AbkA among others) in strains of A. baumannii and Escherichia coli

Interspecies DNA acquisition by a naturally competent Acinetobacter baumannii strain

The human pathogen Acinetobacter baumannii possesses high genetic plasticity and frequently acquires antimicrobial resistance genes. Here we investigated the role of natural transformation in these processes. Genomic DNA from different sources, including from carbapenem-resistant Klebsiella pneumoniae strains, was mixed with A. baumannii A118 cells. Selected transformants were analysed by whole-genome sequencing. In addition, bioinformatics analyses and in silico gene flow prediction were also performed to support the experimental results. Transformant strains included some that became resistant to carbapenems or changed their antimicrobial susceptibility profile. Foreign DNA acquisition was confirmed by whole-genome analysis. The acquired DNA most frequently identified corresponded to mobile genetic elements, antimicrobial resistance genes and operons involved in metabolism. Bioinformatics analyses and in silico gene flow prediction showed continued exchange of genetic material between A. baumannii and K. pneumoniae when they share the same habitat. Natural transformation plays an important role in the plasticity of A. baumannii and concomitantly in the emergence of multidrug-resistant strains.Fil: Traglia, German Matias. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Place, Kori. California State University; Estados UnidosFil: Dotto, Cristian Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; ArgentinaFil: Fernandez, Jennifer. California State University; Estados UnidosFil: Montaña, Sabrina Daiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; ArgentinaFil: Bahiense, Camila dos Santos. California State University; Estados UnidosFil: Soler Bistue, Alfonso J. C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas; ArgentinaFil: Iriarte, Andres. Universidad de la Republica. Facultad de Medicina; UruguayFil: Perez, Federico. Louis Stokes Cleveland Department Of Veterans Affairs; Estados UnidosFil: Tolmasky, Marcelo E.. California State University; Estados UnidosFil: Bonomo, Robert A.. Louis Stokes Cleveland Department Of Veterans Affairs; Estados UnidosFil: Melano, Roberto Gustavo. Public Health Ontario Laboratories; CanadáFil: Ramirez, Maria Soledad. California State University; Estados Unido

Contact-Dependent Growth Inhibition Proteins in Acinetobacter baylyi ADP1

Bacterial contact-dependent growth inhibition (CDI) systems are two-partner secretion systems in which toxic CdiA proteins are exported on the outer membrane by cognate transporter CdiB proteins. Upon binding to specific receptors, the C-terminal toxic (CT) domain, detached from CdiA, is delivered to neighbouring cells. Contacts inhibit the growth of not-self-bacteria, lacking immunity proteins co-expressed with CdiA, but promote cooperative behaviours in “self” bacteria, favouring the formation of biofilm structures. The Acinetobacter baylyi ADP1 strain features two CdiA, which differ significantly in size and have different CT domains. Homologous proteins sharing the same CT domains have been identified in A. baumannii. The growth inhibition property of the two A. baylyi CdiA proteins was supported by competition assays between wild-type cells and mutants lacking immunity genes. However, neither protein plays a role in biofilm formation or adherence to epithelial cells, as proved by assays carried out with knockout mutants. Inhibitory and stimulatory properties may be similarly uncoupled in A. baumannii proteins

Genetic dissection of the type VI secretion system in Acinetobacter and identification of a novel peptidoglycan hydrolase, TagX, required for its biogenesis

The type VI secretion system (T6SS) is a widespread secretory apparatus produced by Gram-negative bacteria that has emerged as a potent mediator of antibacterial activity during interbacterial interactions. Most Acinetobacter species produce a genetically conserved T6SS, although the expression and functionality of this system vary among different strains. Some pathogenic Acinetobacter baumannii strains activate this secretion system via the spontaneous loss of a plasmid carrying T6SS repressors. In this work, we compared the expression of T6SS-related genes via transcriptome sequencing and differential proteomics in cells with and without the plasmid. This approach, together with the mutational analysis of the T6SS clusters, led to the determination of the genetic components required to elaborate a functional T6SS in the nosocomial pathogen A. baumannii and the nonpathogen A. baylyi. By constructing a comprehensive combination of mutants with changes in the T6SS-associated vgrG genes, we delineated their relative contributions to T6SS function. We further determined the importance of two effectors, including an effector-immunity pair, for antibacterial activity. Our genetic analysis led to the identification of an essential membrane-associated structural component named TagX, which we have characterized as a peptidoglycan hydrolase possessing l,d-endopeptidase activity. TagX shows homology to known bacteriophage l,d-endopeptidases and is conserved in the T6SS clusters of several bacterial species. We propose that TagX is the first identified enzyme that fulfills the important role of enabling the transit of T6SS machinery across the peptidoglycan layer of the T6SS-producing bacterium