Accumulation of Antibiotic Resistance Genes in Carbapenem-Resistant Acinetobacter baumannii Isolates Belonging to Lineage 2, Global Clone 1, from Outbreaks in 2012-2013 at a Tehran Burns Hospital

Genomic characteristics of the multiresistant Acinetobacter baumannii global clone 1 reference strain A297/RUH875

OBJECTIVES

Acinetobacter baumannii ST1, also known as global clone 1 (GC1), is a globally distributed lineage associated with antimicrobial resistance (AMR). The multiresistant isolate A297/RUH8751, recovered from a urinary tract infection in the Netherlands in 1984, has served as a reference strain for ST1. We aimed to generate and analyse the complete genome sequence of A297/RUH8751 to provide insights into its genomic features, antibiotic resistance determinants and phylogenetic placement.

METHODS

WGS was performed using Oxford Nanopore GridION and Illumina HiSeq platforms. Assembly was conducted with Autocycler v0.2.1. Genomic features, including antibiotic resistance genes, insertion sequences and restriction-modification systems, were characterized using ResFinder, ISFinder and REBASE. Comparative analyses were conducted with the draft genome of NIPH 527, which also represents RUH875, to assess sequence variations. Phylogenetic analysis was performed to determine the evolutionary placement of A297/RUH875 within GC1.

RESULTS

The complete genome of RUH875 (A297) consists of a 3 965 450 bp chromosome and three plasmids: pA297-1 (pRAY*; 6078 bp), pA297-2 (8731 bp) and pA297-3 (a 200 kb conjugative plasmid). The chromosome harbours the AbaR21 genomic resistance island, carrying seven antibiotic resistance genes and six prophage regions. Notably, bap1 and bap2, biofilm-associated genes, were fully resolved, with bap1 identical to that of A. baumannii A1-the earliest GC1 isolate. Comparative analysis with A1 revealed 122 SNPs, with clustered variations suggesting potential recombination events. Phylogenetic analysis confirmed A297/RUH875 as a distinct lineage within GC1. The completed genome sequence provides a reference, in addition to strain A1, for studying AMR evolution in GC1 and enhances comparative genomic analyses.

Genomic and phenotypic insights into ST164 blaNDM-1-positive Acinetobacter baumannii from intestinal colonization in China

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) poses a critical global threat, especially in ICUs. Yet, reports on ST164 CRAB harboring blaNDM-1 remain scarce. This study investigates two clinical CRAB isolates, L4773hy and L4796hy, derived from intestinal colonization in Hangzhou, China, focusing on their phenotypic and genomic characteristics as well as the broader transmission of ST164 A. baumannii.

METHODS

Bacterial identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) mass spectrometry. Antimicrobial susceptibility was assessed via agar and broth microdilution. Whole-genome sequencing employed Illumina NovaSeq 6000 and Oxford Nanopore platforms. Resistance genes, insertion elements, transposons, and integrons were detected using ResFinder, PlasmidFinder, VFDB, ISFinder, pdifFinder, and IntegronFinder. Strains were typed by MLST, and a phylogenetic tree was constructed with kSNP3.0. Genetic environment diagrams were generated using Easyfig 2.2.5.

RESULTS

Two blaNDM-1-carrying A. baumannii isolates exhibiting extensive resistance to carbapenems, cephalosporins, and fluoroquinolones. Whole-genome sequencing and genetic environment analysis revealed the presence of a conserved structural sequence (ISAba14-ISAba14-aphA-ISAba125-blaNDM-1-bleMBL) on their chromosomes. Phylogenetic and clonal dissemination analysis showed that ST164 CRAB is primarily distributed in China and exhibits clonal spread. Pathogenicity studies indicated that blaNDM-1-positive ST164 strains have enhanced survival under immune pressure but do not display increased virulence in infection models.

CONCLUSION

This study provides the genomic and phenotypic characterization of intestinally colonized ST164 blaNDM-1 positive CRAB in Hangzhou, China. The elucidation of the genetic environment of blaNDM-1 further confirms the clonal dissemination of ST164 isolates, highlighting the importance of enhanced surveillance and infection control measures to mitigate the spread of these multidrug-resistant pathogens.

Characteristics of the Genetic Spread of Carbapenem-Resistant Acinetobacter baumannii in a Tertiary Greek Hospital

Acinetobacter baumannii (Ab) has increasingly been identified as a cause of hospital-acquired infections and epidemics. The rise of carbapenem-resistant Acinetobacter baumannii (CRAB) poses significant challenges in treatment. Nosocomial outbreaks linked to CRAΒ A. baumannii strains have been reported worldwide, including in Greece. This study aimed to analyze the molecular epidemiology trends of multidrug-resistant A. baumannii isolates in a tertiary hospital in Athens, Greece. A total of 43 clinical isolates of extensively drug-resistant (XDRAB), pan-drug-resistant (PDRAB), and CRAB were collected from patients suffering from blood infection, hospitalized between 2016 and 2020 at the internal medicine clinics and the ICU. A.baumannii isolates underwent testing for Ambler class B and D carbapenemases and the detection of ISAba1, and were typed, initially, using pulsed-field gel electrophoresis, and, subsequently, using sequence-based typing and multiplex PCR to determine European Clone lineages. The blaOXA-23 gene accompanied by ISAba1 was prevalent in nearly all A. baumannii isolates, except for one carrying blaOXA-58. The intrinsic blaOXA-51-like gene was found in all isolates. No Ambler class B carbapenemases (VIM, NDM) were detected. Isolates were grouped into four PF-clusters and no one-cluster spread was documented, consistent with the absence of outbreak. The study indicated that XDR/PDR-CRAB isolates predominantly produce OXA-23 carbapenemase and belong to European Clone II. Further research is needed to understand the distribution of resistant bacteria and develop effective prevention and control strategies.

Genotypic and phenotypic mechanisms underlying antimicrobial resistance and synergistic efficacy of rifampicin-based combinations against carbapenem-resistant Acinetobacter baumannii

Purpose

Carbapenem-resistant Acinetobacter baumannii (CRAB) is an urgent concern to public health. This study focuses on exploring the resistance mechanisms and the in vitro results of using rifampicin in combination with conventional antibiotics for the management of CRAB.

Methods

The synergistic and bactericidal effects of rifampicin with conventional antibiotics were evaluated using chequerboard assay and time-kill assay, while the phenotypic and genotypic characteristics of resistant determinants were performed by efflux pump detection and whole genome sequencing on 29 isolates from ICU patients with underlying health diseases.

Results

The isolates showed multidrug resistance, with over 60% showing addictive responses to rifampicin-based combinations at FICI ranging from 0.6 to 0.8. The time-kill assay revealed 99 % killing for rifampicin and minocycline combination in one isolate at 1/4 MIC rifampicin plus 1/4 MIC minocycline, while a bacteriostatic effect was observed at 1/2 MIC rifampici plus 1/2 MIC for a second isolate. Combination with tigecycline resulted in a 99% killing in two out of three isolates with a 2.5-3 log reduction in CFU at 1/4 MIC rifampicin plus 1/4 MIC tigecycline. Rifampicin plus colistin exhibited bactericidal activity against three out of four isolates. The combinations of rifampicin with ciprofloxacin, chloramphenicol, and trimethoprim-sulfamethoxazole were ineffective against the isolates. In addition, a 4-fold reduction in rifampicin MIC was observed in 2 out of 14 isolates in the presence of an efflux pump inhibitor. The pan-genome study demonstrated a progressive evolution with an accessory genome estimated to cover 58% of the matrix. Seven of the ten sequenced isolates belong to sequence type 2 (ST2), while one isolate each was assigned to ST164, ST16, and ST25. Furthermore, 11 plasmids, 34 antimicrobial resistance (AMR) genes, and 65 virulence-associated genes were predicted from the whole genome data. The blaOXA-23blaADC-25, blaOXA-66, blaPER-7, aph(6)-Id, armA, and arr-3 were prevalent among the isolates. Sequence alignment of the bacteria genome to the reference strain revealed a deleterious mutation in the rpoB gene of 4 isolates.

Conclusion

The study suggests that rifampicin in combination with either minocycline, tigecycline, or colistin might be a treatment option for CRAB clinical isolates. In addition, genotypic analysis of the bacteria isolates may inform the clinician of the suitable drug regimen for the management of specific bacteria variants.

Development and clinical validation of a dual ddPCR assay for detecting carbapenem-resistant Acinetobacter baumannii in bloodstream infections

Objective

Acinetobacter baumannii (A. baumannii, AB) represents a major species of Gram-negative bacteria involved in bloodstream infections (BSIs) and shows a high capability of developing antibiotic resistance. Especially, carbapenem-resistant Acinetobacter baumannii (CRAB) becomes more and more prevalent in BSIs. Hence, a rapid and sensitive CRAB detection method is of urgent need to reduce the morbidity and mortality due to CRAB-associated BSIs.

Methods

A dual droplet digital PCR (ddPCR) reaction system was designed for detecting the antibiotic resistance gene OXA-23 and AB-specific gene gltA. Then, the specificity of the primers and probes, limit of detection (LOD), linear range, and accuracy of the assay were evaluated. Furthermore, the established assay approach was validated on 37 clinical isolates and compared with blood culture and drug sensitivity tests.

Results

The dual ddPCR method established in this study demonstrated strong primer and probe specificity, distinguishing CRAB among 21 common clinical pathogens. The method showed excellent precision (3 × 10-4 ng/μL, CV < 25%) and linearity (OXA-23: y = 1.4558x + 4.0981, R2 = 0.9976; gltA: y = 1.2716x + 3.6092, R2 = 0.9949). While the dual qPCR LOD is 3 × 10-3 ng/μL, the dual ddPCR's LOD stands at 3 × 10-4 ng/μL, indicating a higher sensitivity in the latter. When applied to detect 35 patients with BSIs of AB, the results were consistent with clinical blood culture identification and drug sensitivity tests.

Conclusion

The dual ddPCR detection method for OXA-23 and gltA developed in this study exhibits good specificity, excellent linearity, and a higher LOD than qPCR. It demonstrates reproducibility even for minute samples, making it suitable for rapid diagnosis and precision treatment of CRAB in BSIs.

Antiparasitic nitazoxanide potentiates colistin against colistin-resistant Acinetobacter baumannii and Escherichia coli in vitro and in vivo

IMPORTANCE

Colistin is used as a last resort in many infections caused by multidrug-resistant Gram-negative bacteria; however, colistin-resistant (COL-R) is on the rise. Hence, it is critical to develop new antimicrobial strategies to overcome COL-R. We found that nitazoxanide (NTZ) combined with colistin showed notable synergetic antibacterial activity. These findings suggest that the NTZ/colistin combination may provide an effective alternative route to combat COL-R A. baumannii and COL-R Escherichia coli infections.

The Acinetobacter baumannii K70 and K9 capsular polysaccharides consist of related K-units linked by the same Wzy polymerase and cleaved by the same phage depolymerases

IMPORTANCE

Bacteriophage show promise for the treatment of Acinetobacter baumannii infections that resist all therapeutically suitable antibiotics. Many tail-spike depolymerases encoded by phage that are able to degrade A. baumannii capsular polysaccharide (CPS) exhibit specificity for the linkage present between K-units that make up CPS polymers. This linkage is formed by a specific Wzy polymerase, and the ability to predict this linkage using sequence-based methods that identify the Wzy at the K locus could assist with the selection of phage for therapy. However, little is known about the specificity of Wzy polymerase enzymes. Here, we describe a Wzy polymerase that can accommodate two different but similar sugars as one of the residues it links and phage depolymerases that can cleave both types of bond that Wzy forms.

Bibliometric Examination of Global Scientific Research about Carbapenem-Resistant Acinetobacter Baumannii (CRAB)

This review paper presents a comprehensive bibliometric analysis of the global scientific research pertaining to carbapenem-resistant Acinetobacter baumannii (CRAB) from the years 1996 to 2023. The review employs a systematic approach to evaluate the trends, patterns, and collaborative networks within the CRAB research landscape, shedding light on its substantial global health implications. An analysis of the Scopus database reveals that the earliest publication within the CRAB research domain dates back to 1996. By conducting a meticulous examination of publication output, citation trends, author affiliations, and keyword distributions, this paper provides valuable insights into the evolution of research themes and the emergence of new areas of interest concerning CRAB. The findings of this bibliometric analysis prominently feature the most influential author within this field, namely, Higgins PG, who has contributed a remarkable 39 documents to CRAB research. It is noteworthy that China leads in terms of the quantity of published research articles in this domain, whereas the United States occupies the foremost position about citations within the CRAB research sphere. Furthermore, a more profound exploration of the data yields a heightened understanding of the current status of CRAB research, emphasizing potential avenues for future investigations and underscoring the imperative need for collaborative initiatives to address the challenges posed by this antibiotic-resistant pathogen.

Genome-wide identification and oxacillinase OXA distribution characteristics of Acinetobacter spp. based on a global database

Objective

To use genomic analysis to identify Acinetobacter spp. and to explore the distribution characteristics of ß-lactamase oxallicinases (blaOXA) among Acinetobacter species globally.

Methods

Genomes of global Acinetobacter spp. were downloaded from GenBank using Aspera batch. After quality check using CheckM and QUAST software, the genomes were annotated using Prokka software to investigate the distribution of blaOXAs across Acinetobacter spp.; a phylogenetic tree was constructed to explore the evolutionary relationship among the blaOXA genes in Acinetobacter spp. Average-nucleotide identification (ANI) was performed to re-type the Acinetobacter spp. BLASTN comparison analysis was implemented to determine the sequence type (ST) of Acinetobacter baumannii strain.

Results

A total of 7,853 genomes were downloaded, of which only 6,639 were left for further analysis after quality check. Among them, 282 blaOXA variants were identified from the genomes of 5,893 Acinetobacter spp.; blaOXA-23 (n = 3,168, 53.8%) and blaOXA-66 (2,630, 44.6%) were the most frequent blaOXAs, accounting for 52.6% (3,489/6639), and the co-carriage of blaOXA-23 and blaOXA-66 was seen in 2223 (37.7%) strains. The 282 blaOXA variants were divided into 27 clusters according to the phylogenetic tree. The biggest clade was blaOXA-51-family carbapenem-hydrolyzing enzymes composed of 108 blaOXA variants. Overall, 4,923 A. baumannii were identified out of the 6,639 Acinetobacter spp. strains and 291 distinct STs were identified among the 4,904 blaOXA-carrying A. baumannii. The most prevalent ST was ST2 (n = 3,023, 61.6%) followed by ST1 (n = 228, 4.6%).

Conclusion

OXA-like carbapenemases were the main blaOXA-type β-lactamase spread widely across Acinetobacter spp. Both blaOXA-23 and blaOXA-66 were the predominant blaOXAs, among all A. baumannii strains, with ST2 (belonging to CC2) being the main clone disseminated globally.

Identification of a Specific Biomarker of Acinetobacter baumannii Global Clone 1 by Machine Learning and PCR Related to Metabolic Fitness of ESKAPE Pathogens

Since the emergence of high-risk clones worldwide, constant investigations have been undertaken to comprehend the molecular basis that led to their prevalent dissemination in nosocomial settings over time. So far, the complex and multifactorial genetic traits of this type of epidemic clones have allowed only the identification of biomarkers with low specificity. A machine learning algorithm was able to recognize unequivocally a biomarker for early and accurate detection of Acinetobacter baumannii global clone 1 (GC1), one of the most disseminated high-risk clones. A support vector machine model identified the U1 sequence with a length of 367 nucleotides that matched a fragment of the moaCB gene, which encodes the molybdenum cofactor biosynthesis C and B proteins. U1 differentiates specifically between A. baumannii GC1 and non-GC1 strains, becoming a suitable biomarker capable of being translated into clinical settings as a molecular typing method for early diagnosis based on PCR as shown here. Since the metabolic pathways of Mo enzymes have been recognized as putative therapeutic targets for ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens, our findings highlight that machine learning can also be useful in knowledge gaps of high-risk clones and provides noteworthy support to the literature to identify relevant nosocomial biomarkers for other multidrug-resistant high-risk clones. IMPORTANCE A. baumannii GC1 is an important high-risk clone that rapidly develops extreme drug resistance in the nosocomial niche. Furthermore, several strains have been identified worldwide in environmental samples, exacerbating the risk of human interactions. Early diagnosis is mandatory to limit its dissemination and to outline appropriate antibiotic stewardship schedules. A region with a length of 367 bp (U1) within the moaCB gene that is not subjected to lateral genetic transfer or to antibiotic pressures was successfully found by a support vector machine model that predicts A. baumannii GC1 strains. At the same time, research on the group of Mo enzymes proposed this metabolic pathway related to the superbug's metabolism as a potential future drug target site for ESKAPE pathogens due to its central role in bacterial fitness during infection. These findings confirm that machine learning used for the identification of biomarkers of high-risk lineages can also serve to identify putative novel therapeutic target sites.

Emergence and Evolution of OXA-23-Producing ST46Pas-ST462Oxf-KL28-OCL1 Carbapenem-Resistant Acinetobacter baumannii Mediated by a Novel ISAba1-Based Tn7534 Transposon

Carbapenem-resistant Acinetobacter baumannii (CRAB) isolates of global clone 1 (GC1) and global clone 2 (GC2) have been widely reported. Nevertheless, non-GC1 and non-GC2 CRAB strains have been studied less. In particular, no reports concerning sequence type 46 (ST46_Pas) CRAB strains have been described thus far. In this work, the genomic features and possible evolution mechanism of ST46_Pas OXA-23-producing CRAB isolates from clinical specimens are reported for the first time. Antimicrobial susceptibility testing of three ST46_Pas strains revealed identical resistance profiles (resistance to imipenem, meropenem, ciprofloxacin and the combination of cefoperazone/sulbactam at a 2:1 ratio). They were found to belong to ST46_Pas and ST462_Oxf with capsular polysaccharide 28 (KL28) and lipooligosaccharide 1 (OCL1), respectively. Whole-genome sequencing (WGS) revealed that all contained one copy of chromosomal bla_OXA-23, which was located in a novel ISAba1-based Tn7534 composite transposon. In particular, another copy of the Tn7534 composite transposon was identified in an Hgz_103-type plasmid with 9 bp target site duplications (TSDs, ACAACATGC) in the A. baumannii ZHOU strain. As the strains originated from two neighboring intensive care units (ICUs), ST46_Pas OXA-23-producing CRAB strains may have evolved via transposition events or a pdif module. Based on the GenBank database, ST46_Pas strains were collected from various sources; however, most were collected in Hangzhou (China) from 2014 to 2021. Pan-genome analysis revealed 3276 core genes, 0 soft-core genes, 768 shell genes and 443 cloud genes shared among all ST46_Pas strains. In conclusion, the emergence of ST46_Pas CRAB strains might present a new threat to healthcare settings; therefore, effective surveillance is required to prevent further dissemination.

Transmission of antibiotic resistance genes through mobile genetic elements in Acinetobacter baumannii and gene-transfer prevention

Antibiotic resistance is a major global public health concern. Acinetobacter baumannii is a nosocomial pathogen that has emerged as a global threat because of its high levels of resistance to many antibiotics, particularly those considered as last-resort antibiotics, such as carbapenems. Mobile genetic elements (MGEs) play an important role in the dissemination and expression of antibiotic resistance genes (ARGs), including the mobilization of ARGs within and between species. We conducted an in-depth, systematic investigation of the occurrence and dissemination of ARGs associated with MGEs in A. baumannii. We focused on a cross-sectoral approach that integrates humans, animals, and environments. Four strategies for the prevention of ARG dissemination through MGEs have been discussed: prevention of airborne transmission of ARGs using semi-permeable membrane-covered thermophilic composting; application of nanomaterials for the removal of emerging pollutants (antibiotics) and pathogens; tertiary treatment technologies for controlling ARGs and MGEs in wastewater treatment plants; and the removal of ARGs by advanced oxidation techniques. This review contemplates and evaluates the major drivers involved in the transmission of ARGs from the cross-sectoral perspective and ARG-transfer prevention processes.

Mobile genetic elements carrying aminoglycoside resistance genes in Acinetobacter baumannii isolates belonging to global clone 2

Aminoglycosides are used to treat infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) strains. However, resistance to aminoglycosides has increased remarkably in the last few years. Here, we aimed to determine the mobile genetic elements (MGEs) associated with resistance to aminoglycosides in the global clone 2 (GC2) A. baumannii. Among the 315 A. baumannii isolates, 97 isolates were identified as GC2, and 52 of GC2 isolates (53.6%) were resistant to all the aminoglycosides tested. The AbGRI3s carrying armA were detected in 88 GC2 isolates (90.7%), and of them, 17 isolates (19.3%) carried a new variant of AbGRI3 (AbGRI3_ABI221). aphA6 was located in TnaphA6 of 30 isolates out of 55 aphA6-harboring isolates, and 20 isolates were found to harbor TnaphA6 on a RepAci6 plasmid. Tn6020 carrying aphA1b was detected in 51 isolates (52.5%), which was located within AbGRI2 resistance islands. The pRAY^* carrying the aadB gene was detected in 43 isolates (44.3%), and no isolate was found to contain a class 1 integron harboring this gene. The GC2 A. baumannii isolates contained at least one MGE carrying the aminoglycoside resistance gene, located mostly either in the chromosome within AbGRIs or on the plasmids. Thus, it is likely that these MGEs play a role in the dissemination of aminoglycoside resistance genes in GC2 isolates from Iran.

Bacterial Resistance in Hospital-Acquired Infections Acquired in the Intensive Care Unit: A Systematic Review

PURPOSE

In this review we present the status of the prevalence of bacteria resistant to antibiotics and the main antibiotic resistance genes that are reported in infections acquired in intensive care units (ICU) around the world.

METHODS

A systematic review based on the PRISMA guide was carried out, from the Science Direct, Redalyc, Scopus, Hinari, Scielo, Dialnet, PLOS, ProQuest, Taylor, Lilacs and PubMed/Medline databases. Inclusion criteria of this review were original research study published in a scientific journal in a 10-year time span from 1 January 2017 and 30 April 2022.

RESULTS

A total of 1686 studies were identified, but only 114 studies were considered eligible for inclusion. Klebsiella pneumoniae and Escherichia coli resistant to carbapenems and producers of extended-spectrum β-lactamases (ESBL) are the most frequently isolated pathogens in ICUs in Asia, Africa and Latin America. The blaOXA and blaCTX were antibiotic resistance genes (ARG) most commonly reported in different geographic regions (in 30 and 28 studies, respectively). Moreover, multidrug-resistant (MDR) strains were reported in higher frequency in hospital-acquired infections. Reports of MDR strains vary between continents, with the majority of publications being in Asia and between countries, with Egypt and Iran being highlighted. There is a predominance of few bacterial clones with MDR phenotype, for example, clonal complex 5 Methicillin-Resistant Staphylococcus aureus (CC5-MRSA) circulates frequently in hospitals in the United States, clone ST23-K. pneumoniae is reported in India and Iran, and clone ST260 carbapenemase-producing P. aeruginosa in the United States and Estonia.

CONCLUSION

Our systematic review reveals that ESBL- and carbapenemase-producing K. pneumoniae and E. coli are the most problematic bacteria that are reported, mainly in tertiary hospitals in Asia, Africa, and Latin America. We have also found propagation of dominant clones with a high degree of MDR, becoming a problem due to its high capacity to cause morbidity, mortality and additional hospital costs.

Genomic Analysis of Carbapenem-Resistant Acinetobacter baumannii Strains Recovered from Chilean Hospitals Reveals Lineages Specific to South America and Multiple Routes for Acquisition of Antibiotic Resistance Genes

Carbapenem-resistant Acinetobacter baumannii (CRAb) is a public health threat accounting for a significant number of hospital-acquired infections. Despite the importance of this pathogen, there is scarce literature on A. baumannii molecular epidemiology and evolutionary pathways relevant to resistance emergence in South American strains. We analyzed the genomic context of 34 CRAb isolates recovered from clinical samples between 2010 and 2013 from two hospitals in Santiago, Chile, using whole-genome sequencing. Several Institut Pasteur scheme sequence types (STs) were identified among the 34 genomes studied here, including ST1, ST15, ST79, ST162, and ST109. No ST2 (the most widespread sequence type) strain was detected. Chilean isolates were phylogenetically closely related, forming lineages specific to South America (e.g., ST1, ST79, and ST15). The genomic contexts of the resistance genes were diverse: while genes were present in a plasmid in ST15 strains, all genes were chromosomal in ST79 strains. Different variants of a small Rep_3 plasmid played a central role in the acquisition of the oxa58 carbapenem and aacC2 aminoglycoside resistance genes in ST1, ST15, and ST79 strains. The aacC2 gene along with blaTEM were found in a novel transposon named Tn6925 here. Variants of Tn7 were also found to play an important role in the acquisition of the aadA1 and dfrA1 genes. This work draws a detailed picture of the genetic context of antibiotic resistance genes in a set of carbapenem-resistant A. baumannii strains recovered from two Chilean hospitals and reveals a complex evolutionary picture of antibiotic resistance gene acquisition events via multiple routes involving several mobile genetic elements. IMPORTANCE Treating infections caused by carbapenem-resistant A. baumannii (CRAb) has become a global challenge given that CRAb strains are also often resistant to a wide range of antibiotics. Analysis of whole-genome sequence data is now a standard approach for studying the genomic context of antibiotic resistance genes; however, genome sequence data from South American countries are scarce. Here, phylogenetic and genomic analyses of 34 CRAb strains recovered from 2010 to 2013 from two Chilean hospitals revealed a complex picture leading to the generation of resistant lineages specific to South America. From these isolates, we characterized several mobile genetic elements, some of which are described for the first time. The genome sequences and analyses presented here further our understanding of the mechanisms leading to multiple-drug resistance, extensive drug resistance, and pandrug resistance phenotypes in South America. Therefore, this is a significant contribution to elucidating the global molecular epidemiology of CRAb.

Rectal Colonization and Nosocomial Transmission of Carbapenem-Resistant Acinetobacter baumannii in an Intensive Care Unit, Southwest Nigeria

Background

Acinetobacter baumannii are of major human health importance because they cause life-threatening nosocomial infections and often are highly resistant to antimicrobials. Specific multidrug-resistant A. baumannii lineages are implicated in hospital outbreaks globally. We retrospectively investigated a suspected outbreak of carbapenem-resistant A. baumannii (CRAB) colonizing patients in an intensive care unit (ICU) of a tertiary hospital in Southwest Nigeria where genomic surveillance of Acinetobacter has hitherto not been conducted.

Methods

A prospective observational study was conducted among all patients admitted to the ICU between August 2017 and June 2018. Acinetobacter species were isolated from rectal swabs and verified phenotypically with the Biomerieux Vitek 2 system. Whole genome sequencing (WGS) was performed on the Illumina platform to characterize isolates from a suspected outbreak during the study period. Phylogenetic analysis, multilocus sequence typing, and antimicrobial resistance gene prediction were carried out in silico.

Results

Acinetobacter isolates belonging to the A. baumannii complex were recovered from 20 (18.5%) ICU patients. Single nucleotide polymorphism (SNP) analysis and epidemiological information revealed a putative outbreak clone comprising seven CRAB strains belonging to the globally disseminated international clone (IC) 2. These isolates had ≤2 SNP differences, identical antimicrobial resistance and virulence genes, and were all ST1114/1841.

Conclusion

We report a carbapenem-resistant IC2 A. baumannii clone causing an outbreak in an ICU in Nigeria. The study findings underscore the need to strengthen the capacity to detect A. baumannii in human clinical samples in Nigeria and assess which interventions can effectively mitigate CRAB transmission in Nigerian hospital settings.

Genomic and phenotypic analyses of diverse non-clinical Acinetobacter baumannii strains reveals strain-specific virulence and resistance capacity

Acinetobacter baumannii is a critically important pathogen known for its widespread antibiotic resistance and ability to persist in hospital-associated environments. Whilst the majority of A. baumannii infections are hospital-acquired, infections from outside the hospital have been reported with high mortality. Despite this, little is known about the natural environmental reservoir(s) of A. baumannii and the virulence potential underlying non-clinical strains. Here, we report the complete genome sequences of six diverse strains isolated from environments such as river, soil, and industrial sites around the world. Phylogenetic analyses showed that four of these strains were unrelated to representative nosocomial strains and do not share a monophyletic origin, whereas two had sequence types belonging to the global clone lineages GC1 and GC2. Further, the majority of these strains harboured genes linked to virulence and stress protection in nosocomial strains. These genotypic properties correlated well with in vitro virulence phenotypic assays testing resistance to abiotic stresses, serum survival, and capsule formation. Virulence potential was confirmed in vivo, with most environmental strains able to effectively kill Galleria mellonella greater wax moth larvae. Using phenomic arrays and antibiotic resistance profiling, environmental and nosocomial strains were shown to have similar substrate utilisation patterns although environmental strains were distinctly more sensitive to antibiotics. Taken together, these features of environmental A. baumannii strains suggest the existence of a strain-specific distinct gene pools for niche specific adaptation. Furthermore, environmental strains appear to be equally virulent as contemporary nosocomial strains but remain largely antibiotic sensitive.

Interbacterial Transfer of Carbapenem Resistance and Large Antibiotic Resistance Islands by Natural Transformation in Pathogenic Acinetobacter

Acinetobacter baumannii infection poses a major health threat, with recurrent treatment failure due to antibiotic resistance, notably to carbapenems. While genomic analyses of clinical strains indicate that homologous recombination plays a major role in the acquisition of antibiotic resistance genes, the underlying mechanisms of horizontal gene transfer often remain speculative. Our understanding of the acquisition of antibiotic resistance is hampered by the lack of experimental systems able to reproduce genomic observations. We here report the detection of recombination events occurring spontaneously in mixed bacterial populations and which can result in the acquisition of resistance to carbapenems. We show that natural transformation is the main driver of intrastrain but also interstrain recombination events between A. baumannii clinical isolates and pathogenic species of Acinetobacter. We observed that interbacterial natural transformation in mixed populations is more efficient at promoting the acquisition of large resistance islands (AbaR4 and AbaR1) than when the same bacteria are supplied with large amounts of purified genomic DNA. Importantly, analysis of the genomes of the recombinant progeny revealed large recombination tracts (from 13 to 123 kb) similar to those observed in the genomes of clinical isolates. Moreover, we highlight that transforming DNA availability is a key determinant of the rate of recombinants and results from both spontaneous release and interbacterial predatory behavior. In the light of our results, natural transformation should be considered a leading mechanism of genome recombination and horizontal gene transfer of antibiotic resistance genes in Acinetobacter baumannii.

Phylogenomics of two ST1 antibiotic-susceptible non-clinical Acinetobacter baumannii strains reveals multiple lineages and complex evolutionary history in global clone 1

Acinetobacter baumannii is an opportunistic pathogen that is difficult to treat due to its resistance to extreme conditions, including desiccation and antibiotics. Most strains causing outbreaks around the world belong to two main global lineages, namely global clones 1 and 2 (GC1 and GC2). Here, we used a combination of Illumina short read and MinION (Oxford Nanopore) long-read sequence data with a hybrid assembly approach to complete the genome sequence of two antibiotic-sensitive GC1 strains, Ex003 and Ax270, recovered in Lebanon from water and a rectal swab of a cat, respectively. Phylogenetic analysis of Ax270 and Ex003 with 186 publicly available GC1 genomes revealed two major clades, including five main lineages (L1–L5), and four single-isolate lineages outside of the two clades. Ax270 and Ex003, along with AB307-0294 and MRSN7213 (both predicted antibiotic-susceptible isolates) represent these individual lineages. Antibiotic resistance islands and transposons interrupting the comM gene remain important features in L1–L5, with L1 associated with the AbaR-type resistance islands, L2 with AbaR4, L3 strains containing either AbaR4 or its variants as well as Tn6022::ISAba42, and L4 and L5 associated with Tn6022 or its variants. Analysis of the capsule (KL) and outer core (OCL) polysaccharide loci further revealed a complex evolutionary history probably involving many recombination events. As more genomes become available, more GC1 lineages continue to emerge. However, genome sequence data from more diverse geographical regions are needed to draw a more accurate population structure of this globally distributed clone.

Cl415, a carbapenem-resistant Acinetobacter baumannii isolate containing four AbaR4 and a new variant of AbGRI2, represents a novel global clone 2 strain

Objectives

To determine the genetic context of genes conferring antibiotic resistance on the carbapenem-resistant Acinetobacter baumannii Cl415, recovered in 2017 at El Youssef Hospital Centre in Akkar Governorate, North Lebanon.

Methods

Antibiotic resistance phenotype for 22 antibiotics was determined using disc diffusion or MIC determination. The whole-genome sequence of Cl415 was determined using a combination of the Illumina MiSeq and Oxford Nanopore (MinION) platforms. Complete genome was assembled using Unicycler and antibiotic resistance determinants and ISs were identified using ResFinder and ISFinder, respectively.

Results

Cl415 is a global clone 2 (GC2) strain and belongs to the most common STs of this clone, ST2_IP and ST218_OX. Cl415 is resistant to several antibiotics, including aminoglycosides and carbapenems to a high level. Genomic analysis of Cl415 revealed that it carries four chromosomal AbaR4 copies. One copy was found in the comM gene replacing the AbGRI1 island. Cl415 also contains a novel variant of AbGRI2, herein called AbGRI2-15, carrying only the bla_TEM and aphA1 resistance genes. Cl415 belongs to a subclade of GC2 strains that appear to have diverged recently with a wide geographical distribution.

Conclusions

The resistance gene complement of Cl415 was found in the chromosome with four oxa23 located in AbaR4 copies and the remaining genes in a novel variant of the AbGRI2 resistance island. Cl415 was isolated in Lebanon, but phylogenetic analysis suggests that Cl415 represents a new lineage with global distribution within GC2.

Two carbapenem-resistant ST1:ST231:KL1:OCL1 Acinetobacter baumannii strains recovered in Tehran, Iran, carry AbaR31 in the chromosome and AbaR4 and TnaphA6 in a RepAci6 plasmid

Objectives

To analyse the context of genes conferring antibiotic resistance in two carbapenem-resistant Acinetobacter baumannii isolates recovered in Tehran, Iran.

Methods

The antibiotic resistance phenotype for 28 antibiotics was determined using disc diffusion. The whole genome sequences of ABH008 and ABS200 were determined using the Illumina HiSeq X Ten platform. Resistance genes were identified using ResFinder and multilocus sequence types were determined using the Oxford and Institut Pasteur schemes.

Results

Isolates ABH008 and ABS200, recovered in 2012 and 2013, respectively, in two different Tehran hospitals, belong to the common global clone 1 lineage, ST1_IP and ST231_OX. They are resistant to sulfamethoxazole, tetracycline, gentamicin, amikacin, third-generation cephalosporins and carbapenems. Despite being isolated in different hospitals, phylogenetic analysis indicated they are closely related. Consistent with this, both isolates carry catA1, sul1, aacC1 and aadA1 in a novel variant of the AbaR3-type resistance island, named AbaR31. Both isolates are resistant to amikacin and carbapenems owing to aphA6 and oxa23, respectively. The oxa23 gene is located in the AbaR4 resistance island, and aphA6 in TnaphA6, and both mobile elements are in an ∼90 kbp plasmid encoding the putative RepAci6 replication initiation protein. Resistance to third-generation cephalosporins is due to the acquisition by homologous recombination of a 5 kb DNA segment that contains ISAba1-ampC from a ST623 strain.

Conclusions

The resistance gene complements of ABH008 and ABS200 were found in AbaR31 and a plasmid that encodes RepAci6. The close genetic relationship of ABH008 and ABS200, despite each being recovered from different hospitals, indicates transmission between the two hospitals.

Dissemination of novel Tn7 family transposons carrying genes for synthesis and uptake of fimsbactin siderophores among Acinetobacter baumannii isolates

Acinetobacter baumannii is a successful opportunistic pathogen that can compete for iron under iron-limiting conditions. Here, large novel transposons that carry genes for synthesis and transport of the fimsbactin siderophores present in some A. baumannii strains were examined. Tn6171, originally found in the A. baumannii global clone 1 (GC1) lineage 2 isolate D36, includes tns genes encoding proteins related to the TnsA, TnsB, TnsC transposition proteins (50–59 % identity), TnsD targeting protein (43 % identity) and TnsE (31 % identity) of Tn7, and is found in the chromosome downstream of the glmS gene, the preferred location for Tn7, flanked by a 5 bp target site duplication. Tn6171 is bounded by 29 bp inverted repeats and, like Tn7, includes additional TnsB binding sites at each end. Tn6171 or minor variants were detected in the equivalent location in complete or draft genomes of several further A. baumannii isolates belonging to GC1 [sequence type (ST) 1, ST81, ST94, ST328, ST623, ST717], GC2 (ST2) and ST10. However, in some of these isolates the surrounding glmS region was clearly derived from a different A. baumannii lineage, indicating that the transposon may have been acquired by replacement of a segment of the chromosome. A recombination-free phylogeny revealed that there were several transposon acquisition events in GC1. The GC1 isolates were mainly lineage 2, but a potential third lineage was also detected. A related transposon, designated Tn6552, was detected in ATCC 17978 (ST437) and other ST437 isolates. However, the Tn6552 tnsD targeting gene was interrupted by an ISAba12, and Tn6552 is not downstream of glmS.

Molecular Epidemiology and Clone Transmission of Carbapenem-Resistant Acinetobacter baumannii in ICU Rooms

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a major cause of nosocomial infections and hospital outbreaks worldwide, remaining a critical clinical concern. Here we characterized and investigated the phylogenetic relationships of 105 CRAB isolates from an intensive care unit from one hospital in China collected over six years. All strains carried bla_OXA-23, bla_OXA-66 genes for carbapenem resistance, also had high resistance gene, virulence factor, and insertion sequence burdens. Whole-genome sequencing revealed all strains belonged to ST2, the global clone CC2. The phylogenetic analysis based on the core genome showed all isolates were dominated by a single lineage of three clusters and eight different clones. Two clones were popular during the collection time. Using chi-square test to identify the epidemiologically meaningful groupings, we found the significant difference in community structure only existed in strains from separation time. The haplotype and median-joining network analysis revealed genetic differences appeared among clusters and changes occurred overtime in the dominating cluster. Our results highlighted substantial multidrug-resistant CRAB burden in the hospital ICU environment demonstrating potential clone outbreak in the hospital.

CRISPR-based subtyping to track the evolutionary history of a global clone of Acinetobacter baumannii

Acinetobacter baumannii global clone 1 (GC1) is the second most common clone in the global population of A. baumannii isolates and a key cause of hospital-acquired infections. In this study, comparative analysis of the clustered regularly interspaced short palindromic repeats (CRISPR)-based sequence types (CST) was performed to determine the genetic relatedness and track patterns of descent among 187 GC1 isolates, as a complement to the evolutionary inferences from their multilocus sequence types and genome-wide single nucleotide polymorphism (SNP)-based phylogeny. The CST2 cluster, CST2 and all the CSTs descending from CST2, corresponded to GC1 lineage 1. This cluster included 143 of the 187 isolates showing a prevalent geographical distribution worldwide. A well-demarcated group of 13 CSTs, accounting for 33 of the 187 isolates, corresponded to GC1 lineage 2. All the CSTs of this group were characterized by the absence of spacer Ab-18. Many of the GC1 lineage 2 isolates had an epidemiological link to the Middle East and/or were obtained in military healthcare facilities. GC1 lineage 3 was a novel lineage that has so far been limited to Afghanistan, Pakistan and India. Diversification of A. baumannii GC1 into lineages and clades has probably been related to a dynamic expansion after passing a migration bottleneck to enter the hospital environment. We conclude that CRISPR-based subtyping is a convenient method to trace the evolutionary history of particular bacterial clones, such as A. baumannii GC1.

Analysis of Complete Genome Sequence of Acinetobacter baumannii Strain ATCC 19606 Reveals Novel Mobile Genetic Elements and Novel Prophage

Acinetobacter baumannii isolate ATCC 19606 was recovered in the US prior to 1948. It has been used as a reference and model organism in many studies involving antibiotic resistance and pathogenesis of A. baumannii, while, until recently, a complete genome of this strain was not available. Here, we present an analysis of the complete 3.91-Mbp genome sequence, generated via a combination of short-read sequencing (Illumina) and long-read sequencing (MinION), and show it contains two small cryptic plasmids and a novel complete prophage of size 41.2 kb. We also characterised several regions of the ATCC 19606 genome, leading to the identification of a novel cadmium/mercury transposon, which was named Tn6551. ATCC 19606 is an antibiotic-sensitive strain, but a comparative analysis of all publicly available ST52 strains predicts a resistance to modern antibiotics by the accumulation of antibiotic-resistance genes via plasmids in recent isolates that belong to this sequence type.