Dataset Information

Disruption of tetR type regulator adeN by mobile genetic element confers elevated virulence in Acinetobacter baumannii.

ABSTRACT: Acinetobacter baumannii is an important human pathogen and considered as a major threat due to its extreme drug resistance. In this study, the genome of a hyper-virulent MDR strain PKAB07 of A. baumannii isolated from an Indian patient was sequenced and analyzed to understand its mechanisms of virulence, resistance and evolution. Comparative genome analysis of PKAB07 revealed virulence and resistance related genes scattered throughout the genome, instead of being organized as an island, indicating the highly mosaic nature of the genome. Many intermittent horizontal gene transfer events, insertion sequence (IS) element insertions identified were augmenting resistance machinery and elevating the SNP densities in A. baumannii eventually aiding in their swift evolution. ISAba1, the most widely distributed insertion sequence in A. baumannii was found in multiple sites in PKAB07. Out of many ISAba1 insertions, we identified novel insertions in 9 different genes wherein insertional inactivation of adeN (tetR type regulator) was significant. To assess the significance of this disruption in A. baumannii, adeN mutant and complement strains were constructed in A. baumannii ATCC 17978 strain and studied. Biofilm levels were abrogated in the adeN knockout when compared with the wild type and complemented strain of adeN knockout. Virulence of the adeN knockout mutant strain was observed to be high, which was validated by in vitro experiments and Galleria mellonella infection model. The overexpression of adeJ, a major component of AdeIJK efflux pump observed in adeN knockout strain could be the possible reason for the elevated virulence in adeN mutant and PKB07 strain. Knocking out of adeN in ATCC strain led to increased resistance and virulence at par with the PKAB07. Disruption of tetR type regulator adeN by ISAba1 consequently has led to elevated virulence in this pathogen.

SUBMITTER: Saranathan R

PROVIDER: S-EPMC5711439 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Disruption of tetR type regulator adeN by mobile genetic element confers elevated virulence in Acinetobacter baumannii.

Saranathan Rajagopalan R Pagal Sudhakar S Sawant Ajit R AR Tomar Archana A Madhangi M M Sah Suresh S Satti Annapurna A Arunkumar K P KP Prashanth K K

Virulence 20170424 7

Acinetobacter baumannii is an important human pathogen and considered as a major threat due to its extreme drug resistance. In this study, the genome of a hyper-virulent MDR strain PKAB07 of A. baumannii isolated from an Indian patient was sequenced and analyzed to understand its mechanisms of virulence, resistance and evolution. Comparative genome analysis of PKAB07 revealed virulence and resistance related genes scattered throughout the genome, instead of being organized as an island, indicati ...[more]

PMID: 28436748

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Project description:Insertion sequences (IS) are fundamental mediators of genome plasticity with the potential to generate phenotypic variation with significant evolutionary outcomes. Here, a recently active miniature inverted-repeat transposon element (MITE) was identified in a derivative of Acinetobacter baumannii ATCC 17978 after being subjected to stress conditions. Transposition of the novel element led to the disruption of the hns gene, resulting in a characteristic hypermotile phenotype. DNA identity shared between the terminal inverted repeats of this MITE and coresident ISAba12 elements, together with the generation of 9-bp target site duplications, provides strong evidence that ISAba12 elements were responsible for mobilization of the MITE (designated MITE Aba12 ) within this strain. A wider genome-level survey identified MITE Aba12 in 30 additional Acinetobacter genomes at various frequencies and one Moraxella osloensis genome. Ninety MITE Aba12 copies could be identified, of which 40% had target site duplications, indicating recent transposition events. Elements ranged between 111 and 114?bp; 90% were 113?bp in length. Using the MITE Aba12 consensus sequence, putative outward-facing Escherichia coli ?70 promoter sequences in both orientations were identified. The identification of transcripts originating from the promoter in one direction supports the proposal that the element can influence neighboring host gene transcription. The location of MITE Aba12 varied significantly between and within genomes, preferentially integrating into AT-rich regions. Additionally, a copy of MITE Aba12 was identified in a novel 8.5-kb composite transposon, Tn6645, in the M. osloensis CCUG 350 chromosome. Overall, this study shows that MITE Aba12 is the most abundant nonautonomous element currently found in Acinetobacter IMPORTANCE One of the most important weapons in the armory of Acinetobacter is its impressive genetic plasticity, facilitating rapid genetic mutations and rearrangements as well as integration of foreign determinants carried by mobile genetic elements. Of these, IS are considered one of the key forces shaping bacterial genomes and ultimately evolution. We report the identification of a novel nonautonomous IS-derived element present in multiple bacterial species from the Moraxellaceae family and its recent translocation into the hns locus in the A. baumannii ATCC 17978 genome. The latter finding adds new knowledge to only a limited number of documented examples of MITEs in the literature and underscores the plastic nature of the hns locus in A. baumannii MITE Aba12 , and its predicted parent(s), may be a source of substantial adaptive evolution within environmental and clinically relevant bacterial pathogens and, thus, have broad implications for niche-specific adaptation.

Project description:Identification and validation is the first phase of target-based antimicrobial development. BfmR (RstA), a response regulator in a two-component signal transduction system (TCS) in Acinetobacter baumannii, is an intriguing potential antimicrobial target. A unique characteristic of BfmR is that its inhibition would have the dual benefit of significantly decreasing in vivo survival and increasing sensitivity to selected antimicrobials. Studies on the clinically relevant strain AB307-0294 have shown BfmR to be essential in vivo. Here, we demonstrate that this phenotype in strains AB307-0294 and AB908 is mediated, in part, by enabling growth in human ascites fluid and serum. Further, BfmR conferred resistance to complement-mediated bactericidal activity that was independent of capsular polysaccharide. Importantly, BfmR also increased resistance to the clinically important antimicrobials meropenem and colistin. BfmR was highly conserved among A. baumannii strains. The crystal structure of the receiver domain of BfmR was determined, lending insight into putative ligand binding sites. This enabled an in silico ligand binding analysis and a blind docking strategy to assess use as a potential druggable target. Predicted binding hot spots exist at the homodimer interface and the phosphorylation site. These data support pursuing the next step in the development process, which includes determining the degree of inhibition needed to impact growth/survival and the development a BfmR activity assay amenable to high-throughput screening for the identification of inhibitors. Such agents would represent a new class of antimicrobials active against A. baumannii which could be active against other Gram-negative bacilli that possess a TCS with shared homology. IMPORTANCE Increasing antibiotic resistance in bacteria, particularly Gram-negative bacilli, has significantly affected the ability of physicians to treat infections, with resultant increased morbidity, mortality, and health care costs. In fact, some strains of bacteria are resistant to all available antibiotics, such as Acinetobacter baumannii, which is the focus of this report. Therefore, the development of new antibiotics active against these resistant strains is urgently needed. In this study, BfmR is further validated as an intriguing target for a novel class of antibiotics. Successful inactivation of BfmR would confer the multiple benefits of a decreased ability of A. baumannii to survive in human body fluids, increased sensitivity to complement-mediated bactericidal activity and, importantly, increased sensitivity to other antibiotics. Structural studies support the potential for this "druggable" target, as they identify the potential for small-molecule binding at functionally relevant sites. Next-phase high-throughput screening studies utilizing BfmR are warranted.

Dataset Information

Disruption of tetR type regulator adeN by mobile genetic element confers elevated virulence in Acinetobacter baumannii.

Publications

Disruption of tetR type regulator adeN by mobile genetic element confers elevated virulence in Acinetobacter baumannii.

Similar Datasets

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