Complete Genome Sequencing of Acinetobacter baumannii AC1633 and Acinetobacter nosocomialis AC1530 Unveils a Large Multidrug-Resistant Plasmid Encoding the NDM-1 and OXA-58 Carbapenemases

An outbreak of severe or lethal infections by a multidrug-resistant Acinetobacter baumannii ST126 strain carrying a plasmid with blaNDM-1 and blaOXA-58 carbapenemases

Acinetobacter baumannii poses a significant health threat because of its frequent implications in hospital outbreaks and multidrug resistance (MDR). Here, we studied four A. baumannii isolates recovered during a hospital outbreak of severe or fatal cases to elucidate their diversity and factors contributing to their increased virulence and antibiotic resistance. The isolates were identified using MALDI-ToF and characterized using comparative genomics, PCR, and antimicrobial susceptibility tests. They were classified as ST126 and exhibited fewer than five chromosomal single-nucleotide variants and the same extrachromosomal content, indicating that they are a single strain (A. baumannii AB01). A. baumannii AB01 showed an MDR phenotype that could be linked to the carriage of parC and gyrA mutations, efflux transporters, aminoglycoside resistance genes, a class C beta-lactamase, and three carbapenemases, some of which are encoded on a 72 kb plasmid. ST126 is infrequent and has not been reported in Latin America, and our genomic data indicate a plausible origin for A. baumannii AB01 within the Pan Pacific region.

Genomic study of Acinetobacter baumannii strains co-harboring bla OXA-58 and bla NDM-1 reveals a large multidrug-resistant plasmid encoding these carbapenemases in Brazil

Introduction

Acinetobacter baumannii contributes significantly to the global issue of multidrug-resistant (MDR) nosocomial infections. Often, these strains demonstrate resistance to carbapenems (MDR-CRAB), the first-line treatment for infections instigated by MDR A. baumannii. Our study focused on the antimicrobial susceptibility and genomic sequences related to plasmids from 12 clinical isolates of A. baumannii that carry both the blaOXA-58 and bla NDM-1 carbapenemase genes.

Methods

Whole-genome sequencing with long-read technology was employed for the characterization of an A. baumannii plasmid that harbors the bla OXA-58 and blaNDM-1 genes. The location of the bla OXA-58 and bla NDM-1 genes was confirmed through Southern blot hybridization assays. Antimicrobial susceptibility tests were conducted, and molecular characterization was performed using PCR and PFGE.

Results

Multilocus Sequence Typing analysis revealed considerable genetic diversity among bla OXA-58 and bla NDM-1 positive strains in Brazil. It was confirmed that these genes were located on a plasmid larger than 300 kb in isolates from the same hospital, which also carry other antimicrobial resistance genes. Different genetic contexts were observed for the co-occurrence of these carbapenemase-encoding genes in Brazilian strains.

Discussion

The propagation of bla OXA-58 and bla NDM-1 genes on the same plasmid, which also carries other resistance determinants, could potentially lead to the emergence of bacterial strains resistant to multiple classes of antimicrobials. Therefore, the characterization of these strains is of paramount importance for monitoring resistance evolution, curbing their rapid global dissemination, averting outbreaks, and optimizing therapy.

IS26 and the IS26 family: versatile resistance gene movers and genome reorganizers

SUMMARYIn Gram-negative bacteria, the insertion sequence IS26 is highly active in disseminating antibiotic resistance genes. IS26 can recruit a gene or group of genes into the mobile gene pool and support their continued dissemination to new locations by creating pseudo-compound transposons (PCTs) that can be further mobilized by the insertion sequence (IS). IS26 can also enhance expression of adjacent potential resistance genes. IS26 encodes a DDE transposase but has unique properties. It forms cointegrates between two separate DNA molecules using two mechanisms. The well-known copy-in (replicative) route generates an additional IS copy and duplicates the target site. The recently discovered and more efficient and targeted conservative mechanism requires an IS in both participating molecules and does not generate any new sequence. The unit of movement for PCTs, known as a translocatable unit or TU, includes only one IS26. TU formed by homologous recombination between the bounding IS26s can be reincorporated via either cointegration route. However, the targeted conservative reaction is key to generation of arrays of overlapping PCTs seen in resistant pathogens. Using the copy-in route, IS26 can also act on a site in the same DNA molecule, either inverting adjacent DNA or generating an adjacent deletion plus a circular molecule carrying the DNA segment lost and an IS copy. If reincorporated, these circular molecules create a new PCT. IS26 is the best characterized IS in the IS26 family, which includes IS257/IS431, ISSau10, IS1216, IS1006, and IS1008 that are also implicated in spreading resistance genes in Gram-positive and Gram-negative pathogens.

Emergence of an Extensive Drug Resistant Citrobacter portucalensis Clinical Strain Harboring bla SFO-1, bla KPC-2, and bla NDM-1

Background

To explore the plasmid characteristics and transfer mechanisms of an extensive drug resistant (XDR) clinical isolate, Citrobacter portucalensis L2724hy, co-producing bla SFO-1, bla NDM-1, and bla KPC-2.

Methods

Species confirmation of L2724hy was achieved through 16S rRNA sequencing and Average Nucleotide Identity (ANI) analysis. Antimicrobial susceptibility testing (AST) employed the agar dilution and micro broth dilution methods. Identification of resistance genes was carried out by PCR and whole-genome sequencing (WGS). Essential resistance gene locations were verified by S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) and southern hybridization experiments. Subsequent WGS data analysis delved into drug resistance genes and plasmids.

Results

The confirmation of the strain L2724hy as an extensive drug-resistant Citrobacter portucalensis, resistant to almost all antibiotics tested except polymyxin B and tigecycline, was achieved through 16S rRNA sequencing, ANI analysis and AST results. WGS and subsequent analysis revealed L2724hy carrying bla SFO-1, bla NDM-1, and bla KPC-2 on plasmids of various sizes. The uncommon ESBL gene bla SFO-1 coexists with the fosA3 gene on an IncFII plasmid, featuring the genetic environment IS26-fosA3-IS26-ampR-bla SFO-1-IS26. The bla NDM-1 was found on an IncX3 plasmid, coexisting with bla SHV-12, displaying the sequence IS5-IS3000-IS3000-Tn2-bla NDM-1-ble-trpF-dsbD-cutA-gros-groL, lacking ISAa125. The bla KPC-2 is located on an unclassified plasmid, exhibiting the sequence Tn2-tnpR-ISKpn27-bla KPC-2-ISKpn6-korC. Conjugation assays confirmed the transferability of both bla NDM-1 and bla KPC-2.

Conclusion

We discovered the coexistence of bla SFO-1, bla NDM-1, and bla KPC-2 in C. portucalensis for the first time, delving into plasmid characteristics and transfer mechanisms. Our finding highlights the importance of vigilant monitoring of drug-resistance genes and insertion elements in uncommon strains.

Genomic insights into the adaptation of Acinetobacter johnsonii RB2-047 to the heavy metal-contaminated subsurface mine environment

The subsurface mine environments characterized by high levels of toxic metals and low nutrient availability represent an extreme threat to bacterial persistence. In recent study, the genomic analysis of the Acinetobacter johnsonii strain RB2-047 isolated from the Rozália Gold Mine in Slovakia was performed. As expected, the studied isolate showed a high level of heavy metal tolerance (minimum inhibitory concentrations were 500 mg/L for copper and nickel, 1,500 mg/L for lead, and 250 mg/L for zinc). The RB2-047 strain also showed noticeable resistance to several antibiotics (ampicillin, kanamycin, chloramphenicol, tetracycline and ciprofloxacin). The genomic composition analysis demonstrated a low number of antibiotic and metal resistance coding genes, but a high occurrence of efflux transporter genes located on the bacterial chromosome. The experimental inhibition of efflux pumps resulted in decreased tolerance to Zn and Ni (but not to Cu and Pb) and to all antibiotics tested. In addition, the H33342 dye-accumulation assay confirmed the high efflux activity in the RB2-047 isolate. These findings showed the important role of efflux pumps in the adaptation of Acinetobacter johsonii strain RB2-047 to metal polluted mine environment as well as in development of multi-antibiotic resistance.

Variation in the plasmid backbone and dif module content of R3-T33 Acinetobacter plasmids

The predominant type of plasmids found in Acinetobacter species encode a Rep_3 initiation protein and many of these carry their accessory genes in dif modules. Here, available sequences of the 14 members of the group of Rep_3 plasmids typed as R3-T33, using a threshold of 95% identity in the repA gene, were compiled and compared. These plasmids were from various Acinetobacter species. The pdif sites were identified allowing the backbone and dif modules to be defined. As for other Rep_3 plasmids carrying dif modules, orfX encoding a protein of unknown function was found downstream of repA followed by a pdif site in the orientation XerC binding site-spacer-XerD binding site. Most backbones (n = 12) also included mobA and mobC genes but the two plasmids with the most diverged repA and orfX genes had different backbone contents. Although the gene content of the plasmid backbone was largely conserved, extensive recombinational exchange was detected and only two small groups carried identical or nearly identical backbones. Individual plasmids were associated with 1 to 13 dif modules. Many different dif modules were identified, including ones containing antibiotic or chromate resistance genes and several toxin/antitoxin gene pairs. In some cases, modules carrying the same genes were significantly diverged. Generally, the orientation of the pdif sites alternated such that C modules (XerC binding sites internal) alternated with D modules (XerD binding sites internal). However, fusions of two dif modules via mutational inactivation or loss of a pdif site were also detected.

Phylogenomics of Acinetobacter species and analysis of antimicrobial resistance genes

Introduction

Non-baumannii Acinetobacter species are increasingly isolated in the clinical setting and the environment. The aim of the present study was to analyze a genome database of 837 Acinetobacter spp. isolates, which included 798 non-baumannii Acinetobacter genomes, in order to define the concordance of classification and discriminatory power of 7-gene MLST, 53-gene MLST, and single-nucleotide polymorphism (SNPs) phylogenies.

Methods

Phylogenies were performed on Pasteur Multilocus Sequence Typing (MLST) or ribosomal Multilocus Sequence Typing (rMLST) concatenated alleles, or SNPs extracted from core genome alignment.

Results

The Pasteur MLST scheme was able to identify and genotype 72 species in the Acinetobacter genus, with classification results concordant with the ribosomal MLST scheme. The discriminatory power and genotyping reliability of the Pasteur MLST scheme were assessed in comparison to genome-wide SNP phylogeny on 535 non-baumannii Acinetobacter genomes assigned to Acinetobacter pittii, Acinetobacter nosocomialis, Acinetobacter seifertii, and Acinetobacter lactucae (heterotypic synonym of Acinetobacter dijkshoorniae), which were the most clinically relevant non-baumannii species of the A. baumannii group. The Pasteur MLST and SNP phylogenies were congruent at Robinson-Fould and Matching cluster tests and grouped genomes into four and three clusters in A. pittii, respectively, and one each in A. seifertii. Furthermore, A. lactucae genomes were grouped into one cluster within A. pittii genomes. The SNP phylogeny of A. nosocomialis genomes showed a heterogeneous population and did not correspond to the Pasteur MLST phylogeny, which identified two recombinant clusters. The antimicrobial resistance genes belonging to at least three different antimicrobial classes were identified in 91 isolates assigned to 17 distinct species in the Acinetobacter genus. Moreover, the presence of a class D oxacillinase, which is a naturally occurring enzyme in several Acinetobacter species, was found in 503 isolates assigned to 35 Acinetobacter species.

Conclusion

In conclusion, Pasteur MLST phylogeny of non-baumannii Acinetobacter isolates coupled with in silico detection of antimicrobial resistance makes it important to study the population structure and epidemiology of Acinetobacter spp. isolates.

Acinetobacter Non-baumannii Species: Occurrence in Infections in Hospitalized Patients, Identification, and Antibiotic Resistance

BACKGROUND

Acinetobacter species other than A. baumannii are becoming increasingly more important as opportunistic pathogens for humans. The primary aim of this study was to assess the prevalence, species distribution, antimicrobial resistance patterns, and carbapenemase gene content of clinical Acinetobacter non-baumannii (Anb) isolates that were collected as part of a sentinel surveillance program of bacterial infections in hospitalized patients. The secondary aim was to evaluate the performance of MALDI-TOF MS systems for the species-level identification of Anb isolates.

METHODS

Clinical bacterial isolates were collected from multiple sites across Russia and Kazakhstan in 2016-2022. Species identification was performed by means of MALDI-TOF MS, with the Autobio and Bruker systems used in parallel. The PCR detection of the species-specific blaOXA-51-like gene was used as a means of differentiating A. baumannii from Anb species, and the partial sequencing of the rpoB gene was used as a reference method for Anb species identification. The susceptibility of isolates to antibiotics (amikacin, cefepime, ciprofloxacin, colistin, gentamicin, imipenem, meropenem, sulbactam, tigecycline, tobramycin, and trimethoprim-sulfamethoxazole) was determined using the broth microdilution method. The presence of the most common in Acinetobacter-acquired carbapenemase genes (blaOXA-23-like, blaOXA-24/40-like, blaOXA-58-like, blaNDM, blaIMP, and blaVIM) was assessed using real-time PCR.

RESULTS

In total, 234 isolates were identified as belonging to 14 Anb species. These comprised 6.2% of Acinetobacter spp. and 0.7% of all bacterial isolates from the observations. Among the Anb species, the most abundant were A. pittii (42.7%), A. nosocomialis (13.7%), the A. calcoaceticus/oleivorans group (9.0%), A. bereziniae (7.7%), and A. geminorum (6.0%). Notably, two environmental species, A. oleivorans and A. courvalinii, were found for the first time in the clinical samples of patients with urinary tract infections. The prevalence of resistance to different antibiotics in Anb species varied from <4% (meropenem and colistin) to 11.2% (gentamicin). Most isolates were susceptible to all antibiotics; however, sporadic isolates of A. bereziniae, A. johnsonii, A. nosocomialis, A. oleivorans, A. pittii, and A. ursingii were resistant to carbapenems. A. bereziniae was more frequently resistant to sulbactam, aminoglycosides, trimethoprim-sulfamethoxazole, and tigecycline than the other species. Four (1.7%) isolates of A. bereziniae, A. johnsonii, A. pittii were found to carry carbapenemase genes (blaOXA-58-like and blaNDM, either alone or in combination). The overall accuracy rates of the species-level identification of Anb isolates with the Autobio and Bruker systems were 80.8% and 88.5%, with misidentifications occurring in 5 and 3 species, respectively.

CONCLUSIONS

This study provides important new insights into the methods of identification, occurrence, species distribution, and antibiotic resistance traits of clinical Anb isolates.

Identification and genome-wide analysis provide insights into the genetic diversity and biotechnological potentials of novel cold-adapted Acinetobacter strain

Extreme cold environments, such as polar regions or high-altitude mountains, are known for their challenging conditions including low temperatures, high salinity, and limited nutrient availability. Microbes that thrive in these environments have evolved specialized strategies to survive and function under such harsh conditions. The study aims to identify, sequence the genome, perform genome assembly, and conduct a comparative genome-wide analysis of Acinetobacter sp. strain P1, which was isolated from the Batura glacier regions of Pakistan. A basic local alignment search tool of NCBI using 16 s RNA gene sequence confirmed the strain Acinetobacter following phylogenetic analysis revealed that strain P1 clustered with Acinetobacter sp. strain AcBz01. The high-throughput Genome sequencing was done by the NovaSeq 6000 sequencing system following de novo genome assembly reported 23 contigs, a genome size of 3,732,502 bp containing approximately 3489 genes and 63 RNAs (60 tRNA, 3 rRNA). The comparative genome analysis revealed that Acinetobacter sp. strain P1 exhibited the highest homology with the Acinetobacter baumannii ATCC 17978 genome and encompassed 1668 indispensable genes, 1280 conserved genes 1821 specific genes suggesting high genomic plasticity and evolutionary diversity. The genes with functional assignments include exopolysaccharide phosphotransferase enzyme, cold-shock proteins, T6SS, membrane modifications, antibiotic resistance, and set of genes related to a wide range of metabolic characteristics such as exopolysaccharides were also present. Moreover, the structural prediction analysis of EPS proteins reveals that structural flexibility allows for conformational modifications during catalysis, which boosts or increases the catalytic effectiveness at lower temperatures. Overall, the identification of Acinetobacter, a cold-adapted bacterium, offers promising applications in bioremediation, enzyme production, food preservation, pharmaceutical development, and astrobiology. Further research and exploration of these microorganisms can unlock their full biotechnological potential and contribute to various industries and scientific endeavors.

Global Epidemiology and Mechanisms of Resistance of Acinetobacter baumannii-calcoaceticus Complex

Acinetobacter baumannii-calcoaceticus complex is the most commonly identified species in the genus Acinetobacter and it accounts for a large percentage of nosocomial infections, including bacteremia, pneumonia, and infections of the skin and urinary tract. A few key clones of A. baumannii-calcoaceticus are currently responsible for the dissemination of these organisms worldwide. Unfortunately, multidrug resistance is a common trait among these clones due to their unrivalled adaptive nature. A. baumannii-calcoaceticus isolates can accumulate resistance traits by a plethora of mechanisms, including horizontal gene transfer, natural transformation, acquisition of mutations, and mobilization of genetic elements that modulate expression of intrinsic and acquired genes.

The Plasmidomic Landscape of Clinical Methicillin-Resistant Staphylococcus aureus Isolates from Malaysia

Methicillin-resistant Staphylococcus aureus (MRSA) is a priority nosocomial pathogen with plasmids playing a crucial role in its genetic adaptability, particularly in the acquisition and spread of antimicrobial resistance. In this study, the genome sequences of 79 MSRA clinical isolates from Terengganu, Malaysia, (obtained between 2016 and 2020) along with an additional 15 Malaysian MRSA genomes from GenBank were analyzed for their plasmid content. The majority (90%, 85/94) of the Malaysian MRSA isolates harbored 1-4 plasmids each. In total, 189 plasmid sequences were identified ranging in size from 2.3 kb to ca. 58 kb, spanning all seven distinctive plasmid replication initiator (replicase) types. Resistance genes (either to antimicrobials, heavy metals, and/or biocides) were found in 74% (140/189) of these plasmids. Small plasmids (<5 kb) were predominant (63.5%, 120/189) with a RepL replicase plasmid harboring the ermC gene that confers resistance to macrolides, lincosamides, and streptogramin B (MLS_B) identified in 63 MRSA isolates. A low carriage of conjugative plasmids was observed (n = 2), but the majority (64.5%, 122/189) of the non-conjugative plasmids have mobilizable potential. The results obtained enabled us to gain a rare view of the plasmidomic landscape of Malaysian MRSA isolates and reinforces their importance in the evolution of this pathogen.

Dynamic state of plasmid genomic architectures resulting from XerC/D-mediated site-specific recombination in Acinetobacter baumannii Rep_3 superfamily resistance plasmids carrying blaOXA-58 - and TnaphA6-resistance modules

The acquisition of bla _OXA genes encoding different carbapenem-hydrolyzing class-D β-lactamases (CHDL) represents a main determinant of carbapenem resistance in the nosocomial pathogen Acinetobacter baumannii. The bla_OXA-58 gene, in particular, is generally embedded in similar resistance modules (RM) carried by plasmids unique to the Acinetobacter genus lacking self-transferability. The ample variations in the immediate genomic contexts in which bla_OXA-58 -containing RMs are inserted among these plasmids, and the almost invariable presence at their borders of non-identical 28-bp sequences potentially recognized by the host XerC and XerD tyrosine recombinases (pXerC/D-like sites), suggested an involvement of these sites in the lateral mobilization of the gene structures they encircle. However, whether and how these pXerC/D sites participate in this process is only beginning to be understood. Here, we used a series of experimental approaches to analyze the contribution of pXerC/D-mediated site-specific recombination to the generation of structural diversity between resistance plasmids carrying pXerC/D-bounded bla _OXA-58- and TnaphA6-containing RM harbored by two phylogenetically- and epidemiologically-closely related A. baumannii strains of our collection, Ab242 and Ab825, during adaptation to the hospital environment. Our analysis disclosed the existence of different bona fide pairs of recombinationally-active pXerC/D sites in these plasmids, some mediating reversible intramolecular inversions and others reversible plasmid fusions/resolutions. All of the identified recombinationally-active pairs shared identical GGTGTA sequences at the cr spacer separating the XerC- and XerD-binding regions. The fusion of two Ab825 plasmids mediated by a pair of recombinationally-active pXerC/D sites displaying sequence differences at the cr spacer could be inferred on the basis of sequence comparison analysis, but no evidence of reversibility could be obtained in this case. The reversible plasmid genome rearrangements mediated by recombinationally-active pairs of pXerC/D sites reported here probably represents an ancient mechanism of generating structural diversity in the Acinetobacter plasmid pool. This recursive process could facilitate a rapid adaptation of an eventual bacterial host to changing environments, and has certainly contributed to the evolution of Acinetobacter plasmids and the capture and dissemination of bla _OXA-58 genes among Acinetobacter and non-Acinetobacter populations co-residing in the hospital niche.

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.

Evolution of RND efflux pumps in the development of a successful pathogen

AIMS

This study examined the origins and evolution of the AdeABC, AdeFGH and AdeIJK efflux pumps in the Acinetobacter genus, including human and animal pathogens and species from non-clinical environments.

METHODS

Comparative genome analyses were performed using the reference sequences for 70 Acinetobacter species to identify putative orthologs of AdeABC, AdeFGH and AdeIJK and their regulators. Sequence similarities and the genomic locations of coding sequences were correlated with phylogeny to infer modes of evolution. Intraspecies variation was assessed in species of interest using up to 236 complete genome sequences. Mutants overproducing adeIJK in A. baylyi were examined to identify regulators of this system in a non A. baumannii species.

RESULTS

The results indicate that adeIJK has been a stable part of Acinetobacter genomes since the genesis of this genus, whereas adeABC and adeFGH were carried by less than half of the species, but showed some lineage specificity. The organisation and local genetic contexts of adeABC loci were particularly variable to the sub-species level, suggesting frequent recombination. Cognate regulatory systems were almost always found in the genomes of species encoding pumps. Mutations in adeN, which encodes a repressor of adeIJK, were selected by antibiotic exposure in A. baylyi, similar to previous findings in pathogenic lineages.

CONCLUSIONS

The multidrug efflux capacity of clinical Acinetobacter strains stems from accessory and core genetic features. AdeIJK is likely to have ancient core function(s) that have promoted its maintenance, whereas recent antibiotic use may be driving the evolution of the AdeABC pump.

Comparative genomic analysis of clinical Acinetobacter nosocomialis isolates from Terengganu, Malaysia led to the discovery of a novel tetracycline-resistant plasmid

OBJECTIVES

To analyse the genome sequences of four archival Acinetobacter nosocomialis clinical isolates (designated AC13, AC15, AC21 and AC25) obtained from Terengganu, Malaysia in 2011 to determine their genetic relatedness and basis of antimicrobial resistance.

METHODS

Antimicrobial susceptibility profiles of the A. nosocomialis isolates were determined by disk diffusion. Genome sequencing was performed using the Illumina NextSeq platform.

RESULTS

The four A. nosocomialis isolates were cefotaxime resistant whereas three isolates (namely, AC13, AC15 and AC25) were tetracycline resistant. The carriage of the bla_ADC-255-encoded cephalosporinase gene is likely responsible for cefotaxime resistance in all four isolates. Phylogenetic analysis indicated that the three tetracycline-resistant isolates were closely related, with an average nucleotide identity of 99.9%, suggestive of nosocomial spread, whereas AC21 had an average nucleotide identity of 97.9% when compared to these three isolates. The tetracycline-resistant isolates harboured two plasmids: a 13476 bp Rep3-family plasmid of the GR17 group designated pAC13-1, which encodes the tetA(39) tetracycline-resistance gene, and pAC13-2, a 4872 bp cryptic PriCT-1-family plasmid of a new Acinetobacter plasmid group, GR60. The tetA(39) gene was in a 2 001 bp fragment flanked by XerC/XerD recombination sites characteristic of a mobile pdif module. Both plasmids also harboured mobilisation/transfer-related genes.

CONCLUSIONS

Genome sequencing of A. nosocomialis isolates led to the discovery of two novel plasmids, one of which encodes the tetA(39) tetracycline-resistant gene in a mobile pdif module. The high degree of genetic relatedness among the three tetracycline-resistant A. nosocomialis isolates is indicative of nosocomial transmission.

GR13-type plasmids in Acinetobacter potentiate the accumulation and horizontal transfer of diverse accessory genes

Carbapenem and other antibiotic resistance genes (ARGs) can be found in plasmids in Acinetobacter, but many plasmid types in this genus have not been well-characterized. Here we describe the distribution, diversity and evolutionary capacity of rep group 13 (GR13) plasmids that are found in Acinetobacter species from diverse environments. Our investigation was prompted by the discovery of two GR13 plasmids in A. baumannii isolated in an intensive care unit (ICU). The plasmids harbour distinct accessory genes: pDETAB5 contains bla_NDM-1 and genes that confer resistance to four further antibiotic classes, while pDETAB13 carries putative alcohol tolerance determinants. Both plasmids contain multiple dif modules, which are flanked by pdif sites recognized by XerC/XerD tyrosine recombinases. The ARG-containing dif modules in pDETAB5 are almost identical to those found in pDETAB2, a GR34 plasmid from an unrelated A. baumannii isolated in the same ICU a month prior. Examination of a further 41 complete, publicly available plasmid sequences revealed that the GR13 pangenome consists of just four core but 1186 accessory genes, 123 in the shell and 1063 in the cloud, reflecting substantial capacity for diversification. The GR13 core genome includes genes for replication and partitioning, and for a putative tyrosine recombinase. Accessory segments encode proteins with diverse putative functions, including for metabolism, antibiotic/heavy metal/alcohol tolerance, restriction-modification, an anti-phage system and multiple toxin–antitoxin systems. The movement of dif modules and actions of insertion sequences play an important role in generating diversity in GR13 plasmids. Discrete GR13 plasmid lineages are internationally disseminated and found in multiple Acinetobacter species, which suggests they are important platforms for the accumulation, horizontal transmission and persistence of accessory genes in this genus.

Dissemination and Genetic Relatedness of Multidrug-Resistant and Extensively Drug-Resistant Acinetobacter baumannii Isolates from a Burn Hospital in Iraq

Acinetobacter baumannii is an aggressive opportunistic bacterial pathogen that causes severe nosocomial infections, especially among burn patients. An increasing number of hospitals-acquired infections have been reported all over the world. However, little attention has been paid to the relatedness between A. baumannii isolates from different hospital environments and patients. In this study, 27 isolates were collected from the Burn and Plastic Surgery Hospital of Al Sulaymaniyah City, Iraq, from January through December 2019 (11 from patients and 16 from the wards environment), identified to species level as A. baumannii using Vitek 2 system and molecular detection of 16S rRNA gene, and then confirmed by targeting the bla_OXA-51 gene. Moreover, the isolates were characterized by means of automated antimicrobial susceptibility assay, antimicrobial-resistant patterns, a phenotypic method using a combined disk test, and molecular methods for the detection of class A and C β-lactamase genes, and finally, the genetic relatedness was classified. Antimicrobial susceptibility testing showed that 63% (17/27) of the retrieved A. baumannii isolates were extensively drug-resistant to 8/9 antimicrobial classes. Furthermore, 37% (10/27) of the isolates were classified as multidrug-resistant; 8 isolates exhibited similar resistant patterns and the other two isolates showed 2 different patterns, while resistance was greater in isolates from patients than from the ward environment. Combined disk test showed that two isolates contained extended-spectrum β-lactamase. All isolates carried bla_TEM-1, and two copies of the bla_CTX-1 gene were indicated in one isolate, while bla_SHV was absent in all isolates. Twenty-four isolates carried the bla_AmpC gene; among them, 3 isolates harbored the insertion sequence ISAba-1 upstream to the gene. Using Enterobacterial Repetitive Intergenic Consensus PCR, the isolates were clustered into 6 distinct types; among them, two clusters, each of four strains, were classified to contain isolates from both patients and environments. The clusters of similar genotypes were found in inpatients as well as the environments of different wards during time periods, suggesting transmission within the hospital. Identification of possible infection sources and controlling the transmission of these aggressive resistance strains should be strictly conducted.