Novel ISCR1-linked resistance genes found in multidrug-resistant Gram-negative bacteria in southern China

A Decade-Long Evaluation of Neonatal Septicaemic Escherichia coli: Clonal Lineages, Genomes, and New Delhi Metallo-Beta-Lactamase Variants

Longitudinal studies of extraintestinal pathogenic Escherichia coli (ExPEC) and epidemic clones of E. coli in association with New Delhi metallo-β-lactamase (blaNDM) in septicaemic neonates are rare. This study captured the diversity of 80 E. coli isolates collected from septicaemic neonates in terms of antibiotic susceptibility, resistome, phylogroups, sequence types (ST), virulome, plasmids, and integron types over a decade (2009 to 2019). Most of the isolates were multidrug-resistant and, 44% of them were carbapenem-resistant, primarily due to blaNDM. NDM-1 was the sole NDM-variant present in conjugative IncFIA/FIB/FII replicons until 2013, and it was subsequently replaced by other variants, such as NDM-5/-7 found in IncX3/FII. A core genome analysis for blaNDM+ve isolates showed the heterogeneity of the isolates. Fifty percent of the infections were caused by isolates of phylogroups B2 (34%), D (11.25%), and F (4%), whereas the other half were caused by phylogroups A (25%), B1 (11.25%), and C (14%). The isolates were further distributed in approximately 20 clonal complexes (STC), including five epidemic clones (ST131, ST167, ST410, ST648, and ST405). ST167 and ST131 (subclade H30Rx) were dominant, with most of the ST167 being blaNDM+ve and blaCTX-M-15+ve. In contrast, the majority of ST131 isolates were blaNDM-ve but blaCTX-M-15+ve, and they possessed more virulence determinants than did ST167. A single nucleotide polymorphism (SNP)-based comparative genome analysis of epidemic clones ST167 and ST131 in a global context revealed that the study isolates were present in close proximity but were distant from global isolates. The presence of antibiotic-resistant epidemic clones causing sepsis calls for a modification of the recommended antibiotics with which to treat neonatal sepsis. IMPORTANCE Multidrug-resistant and virulent ExPEC causing sepsis in neonates is a challenge to neonatal health. The presence of enzymes, such as carbapenemases (blaNDM) that hydrolyze most β-lactam antibiotic compounds, result in difficulties when treating neonates. The characterization of ExPECs collected over 10 years showed that 44% of ExPECs were carbapenem-resistant, possessing transmissible blaNDM genes. The isolates belonged to different phylogroups that are considered to be either commensals or virulent. The isolates were distributed in around 20 clonal complexes (STC), including two predominant epidemic clones (ST131 and ST167). ST167 possessed few virulence determinants but was blaNDM+ve. In contrast, ST131 harbored several virulence determinants but was blaNDM-ve. A comparison of the genomes of these epidemic clones in a global context revealed that the study isolates were present in close proximity but were distant from global isolates. The presence of epidemic clones in a vulnerable population with contrasting characteristics and the presence of resistance genes call for strict vigilance.

Detection of Two Copies of a blaNDM-1-Encoding Plasmid in Escherichia coli Isolates from a Pediatric Patient with Diarrhea

Purpose

To elucidate the contribution of a transferable plasmid harboring the bla_NDM-1 gene in an Escherichia coli clinical isolate to the spread of resistance determinants.

Methods

Nine extended-spectrum β-lactamase-producing E. coli were collected from diarrhea samples from a pediatric patient and genetic linkage was investigated through enterobacteriaceae repetitive intragenic consensus polymerase chain reaction (PCR). Bacterial species were identified by 16s rRNA sequencing, susceptibility testing with the use of a BD Phoenix^TM-100 Automated Microbiology System, and assessment of virulence genes by PCR. The transferability of bla_NDM-1 in E. coli strain TCM3e1 was confirmed by conjugation experiments. Complete sequencing of E. coli strain TCM3e1 was determined with the PacBio and Illumina NovaSeq platforms and the characteristics were analyzed with bioinformatics software.

Results

The results showed that all nine E. coli strains were the same clone. E. coli strain TCM3e1 was resistant to 12 antimicrobial agents and carried the virulence gene EAST-1. Conjugation transfer analysis showed that bla_NDM-1 was carried on a self-transmissible plasmid. Two copies of the bla_NDM-1 gene were present on an IncC plasmid and some resistance genes with two or three copies were located downstream of the bla_NDM-1 gene and formed a tandem repeat fragment (bla_DNM-1-bleo-sul1- aadA17- dfrA12).

Conclusion

A transmissible plasmid harboring two copies of the bla_NDM-1 gene, including clonal dispersions of the bla_NDM-1 gene, was identified in clinical isolates. These findings emphasized the necessity of surveillance of the plasmid-borne bla_NDM-1 to prevent dissemination.

Rapid detection of a novel B1-β-lactamase gene, blaAFM-1 using a loop-mediated isothermal amplification (LAMP) assay

Background

BlaAFM-1 (GenBank Accession No. 143105.1) is a new B1 subclass metallo-β-lactamase gene discovered by our group, and isolated from an Alcaligenes faecalis plasmid that renders carbapenem antibiotics ineffective. In this study, we generated a fast and reliable assay for blaAFM-1 detection.

Methods

We designed optimum loop-mediated isothermal amplification (LAMP) primers and constructed a recombinant plasmid AFM-1 to specifically detect blaAFM-1. Optimal LAMP primers were used to assess sensitivity of the recombinant plasmid AFM-1 and blaAFM-1-supplemented samples (simulated sputum and simulated feces). Fifty two samples, without blaAFM-1, were used to assess LAMP real-time assay specificity; these samples were verified by conventional PCR and sequencing for the absence of blaAFM-1. Three hundred clinical Gram-negative carbapenem-resistant strains were tested by LAMP assay for strains carrying blaAFM-1, which were confirmed by conventional PCR and Sanger sequencing. We calculated the sensitivity and its 95% confidence interval (95% CI), specificity and its 95% CI, and predictive values of the LAMP assay and conventional PCR/sequencing by investigating positive and negative clinical strains.

Results

The lowest limit of detection for the recombinant plasmid AFM-1 and blaAFM-1-supplemented samples (in both simulated sputum and simulated feces) was 10¹ copies/reaction. All amplification curves of the 52 blaAFM-1-free bacteria strains were negative, suggesting the LAMP assay had excellent specificity for detecting blaAFM-1. Among the 300 clinical strains, eight were positive for blaAFM-1 using LAMP. These LAMP results were consistent with conventional PCR and Sanger sequencing data. As with conventional PCR/sequencing, the LAMP method exhibits 100% sensitivity (95% CI 59.8–100%) and 100% specificity (95% CI 98.4–100%) for blaAFM-1 detection. The LAMP assay is also time-efficient (1 h) for blaAFM-1 detection.

Conclusions

We established a new LAMP assay with high sensitivity and specificity to detect the novel B1-β-lactamase gene, blaAFM-1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-021-00486-z.

Fluoroquinolone resistance contributing mechanisms and genotypes of ciprofloxacin- unsusceptible Pseudomonas aeruginosa strains in Iran: emergence of isolates carrying qnr/aac(6)-Ib genes

BACKGROUND

Fluoroquinolones (FQs) including ciprofloxacin (CIP) are key antibiotics for the treatment of Pseudomonas aeruginosa infections, but resistance to FQs is developing as a result of chromosomal mutations or efflux pump effects. Plasmid-mediated quinolone resistance (PMQR) has been recently reported in the Enterobacteriaceae family. This study aimed to investigate the mechanisms of CIP insusceptibility in P. aeruginosa isolates from ICU patients and to characterize their genotypes.

METHODS

A total of 40 ciprofloxacin unsusceptible (CIP-US) P. aeruginosa isolates from Tehran hospitals were recruited in this study. A broth microdilution assay was performed to find acquired resistance profiles of the isolates. All isolates were screened for target-site mutations (gyrA and parC), PMQR genes, and efflux pumps (mexB, D, Y, and E) expression. Clonality was determined by random amplified polymorphic DNA (RAPD)-PCR, and genotyping was performed on 5 selected isolates by analyzing 7 loci in the existing multilocus sequence typing scheme.

RESULTS

Thirty-eight out of 40 CIP-US isolates (95%) were categorized as MDR. Seven (17.5%) had gyrA mutation in codons 83, and no mutation was detected in parC; 77.5% of the isolates were positive for PMQR genes. Among PMQR genes, qnrB (30%), qnrC (35%), and qnrD (30%) predominated, while qnrA, qnrS, and aac(6)-Ib genes were harbored by 20.5%, 12.5%, and 15% of the isolates respectively. Efflux pump protein expression was observed in 35% of the isolates. After RAPD-PCR, 19 different genotypes were yielded, and 5 of them were classified into sequence types (STs): 773, 1160, 2011, 2386, and 359.

CONCLUSION

In this first-time study on P. aeruginosa CIP-US strains from Iranian ICU patients, three main CIP unsusceptibility mechanisms were investigated. A single mutation in one CIP target enzyme could explain high CIP resistance. qnr genes in the isolates can be considered as a CIP-unsusceptibility mechanism among studied isolates. Efflux pumps have more contribution in multidrug resistance than CIP susceptibility. CIP-US isolates of this study have not spread from distinct clonal strains and probably emerged from different sources. STs identified for the first time in this study in Iran should be considered as emerging MDR strains.

Identification of a Novel Metallo-β-Lactamase, VAM-1, in a Foodborne Vibrio alginolyticus Isolate from China

A multidrug-resistant Vibrio alginolyticus isolate recovered from a shrimp sample with reduced carbapenem susceptibility produced a novel metallo-β-lactamase (MBL), VAM-1. That carbapenemase shared 67% to 70% amino acid identity with several VMB family subclass B1 MBLs, which were recently reported among some marine bacteria including Vibrio, Glaciecola, and Thalassomonas. The blaVAM-1 gene was located in a novel conjugative plasmid, namely, pC1579, and multiple copies of blaVAM-1 via an unusual mechanism of gene amplification were detected in pC1579. These findings underline the emergence of marine organisms acting as natural reservoirs for MBL genes and the importance of continuous bacterial antibiotic resistance surveillance.

Gene-Gene Interactions Dictate Ciprofloxacin Resistance in Pseudomonas aeruginosa and Facilitate Prediction of Resistance Phenotype from Genome Sequence Data

Ciprofloxacin is one of the most widely used antibiotics for treating Pseudomonas aeruginosa infections. However, P. aeruginosa acquires mutations that confer ciprofloxacin resistance, making treatment more difficult. Resistance is multifactorial, with mutations in multiple genes influencing the resistance phenotype. However, the contributions of individual mutations and mutation combinations to the amounts of ciprofloxacin that P. aeruginosa can tolerate are not well understood. Engineering P. aeruginosa strain PAO1 to contain mutations in any one of the resistance-associated genes gyrA, nfxB, rnfC, parC, and parE showed that only gyrA mutations increased the MIC for ciprofloxacin. Mutations in parC and parE increased the MIC of a gyrA mutant, making the bacteria ciprofloxacin resistant. Mutations in nfxB and rnfC increased the MIC, conferring resistance, only if both were mutated in a gyrA background. Mutations in all of gyrA, nfxB, rnfC, and parC/E further increased the MIC. These findings reveal an epistatic network of gene-gene interactions in ciprofloxacin resistance. We used this information to predict ciprofloxacin resistance/susceptibility for 274 isolates of P. aeruginosa from their genome sequences. Antibiotic susceptibility profiles were predicted correctly for 84% of the isolates. The majority of isolates for which prediction was unsuccessful were ciprofloxacin resistant, demonstrating the involvement of additional as yet unidentified genes and mutations in resistance. Our data show that gene-gene interactions can play an important role in antibiotic resistance and can be successfully incorporated into models predicting resistance phenotype.

Molecular mechanisms associated with quinolone resistance in Enterobacteriaceae: review and update

BACKGROUND

Quinolones are broad-spectrum antibiotics, which are used for the treatment of different infectious diseases associated with Enterobacteriaceae. During recent decades, the wide use as well as overuse of quinolones against diverse infections has led to the emergence of quinolone-resistant bacterial strains. Herein, we present the development of quinolone antibiotics, their function and also the different quinolone resistance mechanisms in Enterobacteriaceae by reviewing recent literature.

METHODS

All data were extracted from Google Scholar search engine and PubMed site, using keywords; quinolone resistance, Enterobacteriaceae, plasmid-mediated quinolone resistance, etc.

RESULTS AND CONCLUSION

The acquisition of resistance to quinolones is a complex and multifactorial process. The main resistance mechanisms consist of one or a combination of target-site gene mutations altering the drug-binding affinity of target enzymes. Other mechanisms of quinolone resistance are overexpression of AcrAB-tolC multidrug-resistant efflux pumps and downexpression of porins as well as plasmid-encoded resistance proteins including Qnr protection proteins, aminoglycoside acetyltransferase (AAC(6')-Ib-cr) and plasmid-encoded active efflux pumps such as OqxAB and QepA. The elucidation of resistance mechanisms will help researchers to explore new drugs against the resistant strains.

Insight into effect of high-level cephalexin on fate and driver mechanism of antibiotics resistance genes in antibiotic wastewater treatment system

In the study, antibiotic resistance genes (ARGs) were examined in wastewater and sludge samples to explore the effect of cephalexin (CFX) on the spreading and removal of ARGs in the Expanded Granular Sludge Bed (EGSB) reactor treating antibiotics wastewater. The result showed that the addition of CFX in the wastewater affected the removal amount of β-lactam ARGs and other types ARGs. Besides, the addition of CFX in the wastewater had no obviously effect on total concentration of targeted ARGs in the sludge, but it was related to the accumulation of some typical ARGs. Based on gene cassette array libraries analysis, the diversity of gene cassettes carried by intI1 gene was increased by the addition of CFX in the wastewater. Furthermore, the co-occurrence patterns between ARGs and bacterial genus were also investigated. The results showed the CFX in the wastewater not only affected the number of potential host bacteria of ARGs, but also changed the types of potential host bacteria of ARGs. The correlation analysis of ARG in influent, effluent and sludge showed that, for blaCTX-M, sul2, qnrS and AmpC genes, their removal amount in EGSB reactor treating antibiotic wastewater system might be enhanced by reducing their concentration in the sludge.

Multiple mechanisms contributing to ciprofloxacin resistance among Gram negative bacteria causing infections to cancer patients

Fluoroquinolones have been used for prophylaxis against infections in cancer patients but their impact on the resistance mechanisms still require further investigation. To elucidate mechanisms underlying ciprofloxacin (CIP) resistance in Gram-negative pathogens causing infections to cancer patients, 169 isolates were investigated. Broth microdilution assays showed high-level CIP resistance in 89.3% of the isolates. Target site mutations were analyzed using PCR and DNA sequencing in 15 selected isolates. Of them, all had gyrA mutations (codons 83 and 87) with parC mutations (codons 80 and 84) in 93.3%. All isolates were screened for plasmid-mediated quinolone resistance (PMQR) genes and 56.8% of them were positive in this respect. Among PMQR genes, aac(6′)-Ib-cr predominated (42.6%) while qnr genes were harbored by 32.5%. This comprised qnrS in 26.6% and qnrB in 6.5%. Clonality of the qnr-positive isolates using ERIC-PCR revealed that most of them were not clonal. CIP MIC reduction by CCCP, an efflux pump inhibitor, was studied and the results revealed that contribution of efflux activity was observed in 18.3% of the isolates. Furthermore, most fluoroquinolone resistance mechanisms were detected among Gram-negative isolates recovered from cancer patients. Target site mutations had the highest impact on CIP resistance as compared to PMQRs and efflux activity.

Occurrence of antibiotic resistance genes and mobile genetic elements in enterococci and genomic DNA during anaerobic digestion of pharmaceutical waste sludge with different pretreatments

Pharmaceutical waste sludge harbors large amounts of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), and it is necessary to study the reduction of ARGs and MGEs during sludge treatment. Therefore, the antibiotic resistance phenotypes and genotypes of enterococci, and the ARGs and MGEs in genomic DNA were investigated during anaerobic digestion (AD) with microwave (MW), thermal hydrolysis (TH) and ozone pretreatment. Results showed that sludge pretreatment increased the occurrence of the resistance phenotypes and genotypes of enterococci. During AD, the resistance of enterococci to macrolides decreased, except for in the MW-pretreated sludge. Horizontal gene transfer and co-occurrence of ermB and tetM in enterococci resulted in increased tetracycline resistance of enterococci throughout the sludge treatment. MGEs such as intI1, ISCR1 and Tn916/1545 had a significant effect on the distribution of ARGs. AD with pretreatment, especially TH pretreatment, resulted in greater ARGs and MGEs reduction and improved methane production.

Detection of an Escherichia coli Sequence Type 167 Strain with Two Tandem Copies of blaNDM-1 in the Chromosome

New Delhi metallo-β-lactamase-1 (NDM-1)-producing Enterobacteriaceae has disseminated rapidly throughout the world and poses an urgent threat to public health. Previous studies confirmed that the bla_NDM-1 gene is typically carried in plasmids but rarely in chromosome. We discovered a multidrug-resistant Escherichia coli strain Y5, originating from a urine sample and containing the bla_NDM-1 gene, which did not transfer by either conjugation or electrotransformation. We confirmed the possibility of its chromosome location by S1-pulsed-field gel electrophoresis (PFGE) and XbaI-PFGE, followed by Southern blotting. To determine the genomic background of bla_NDM-1, the genome of Y5 was completely sequenced and compared to other reference genomes. The results of our study revealed that this isolate consists of a 4.8-Mbp chromosome and three plasmids, it is an epidemic clone of sequence type (ST) 167, and it shows 99% identity with Escherichia coli 6409 (GenBank accession no. CP010371), which lacks the same bla_NDM-1 gene-surrounding structure as Y5. The bla_NDM-1 gene is embedded in the chromosome along with two tandem copies of an insertion sequence common region 1 (ISCR1) element (sul1-ARR-3-cat-bla_NDM-1-bleo-ISCR1), which appears intact in the plasmid from Proteus mirabilis (GenBank accession no. KP662515). The genomic context indicates that the ISCR1 element mediated the bla_NDM-1 transposition from a single source plasmid to the chromosome. Our study is the first report of an Enterobacteriaceae strain harboring a chromosomally integrated bla_NDM-1, which directly reveals the vertical spreading pattern of the gene. Close surveillance is urgently needed to monitor the emergence and potential spread of ST167 strains that harbor bla_NDM-1.

New structures simultaneously harboring class 1 integron and ISCR1-linked resistance genes in multidrug-resistant Gram-negative bacteria

BACKGROUND

The connection structure of class 1 integron and insertion sequence common region 1 (ISCR1) is called "complex class 1 integrons" or "complex sul1-type integrons", which is also known to be associated with many resistance genes. This structure is a powerful gene-capturing tool kit that can mobilize antibiotic resistance genes. In order to look for and study the structure among clinical multidrug-resistant (MDR) Gram-negative isolates, 63 isolates simultaneously harbored class 1 integron and ISCR1-linked resistance genes were isolated from 2309 clinical non-redundant MDR Gram-negative isolates in Nanfang Hospital in 2008-2013. The connecting regions between the class 1 integrons and ISCR1 were examined using PCR and DNA sequencing to determine the structures in these isolates.

RESULT

The two elements (the variable regions of the class 1 integron structures and the ISCR1-linked resistance genes) are connected in series among 63 isolates according to long-extension PCR and DNA sequencing. According to the kinds and permutations of resistance genes in the structure, 12 distinct types were identified, including 8 types that have never been described in any species. Several types of these structures are similar with the structures of other reports, but not entirely same.

CONCLUSION

This study is the first to determine the structure simultaneously harboring class 1 integron and ISCR1-linked resistance genes by detecting the region connecting class 1 integrons and ISCR1 in a large number of MDR bacteria. These structures carrying various resistance genes were closely associated with multidrug resistance bacteria in Southern China.

Plasmid-mediated quinolone resistance

Three mechanisms for plasmid-mediated quinolone resistance (PMQR) have been discovered since 1998. Plasmid genes qnrA, qnrB, qnrC, qnrD, qnrS, and qnrVC code for proteins of the pentapeptide repeat family that protects DNA gyrase and topoisomerase IV from quinolone inhibition. The qnr genes appear to have been acquired from chromosomal genes in aquatic bacteria, are usually associated with mobilizing or transposable elements on plasmids, and are often incorporated into sul1-type integrons. The second plasmid-mediated mechanism involves acetylation of quinolones with an appropriate amino nitrogen target by a variant of the common aminoglycoside acetyltransferase AAC(6')-Ib. The third mechanism is enhanced efflux produced by plasmid genes for pumps QepAB and OqxAB. PMQR has been found in clinical and environmental isolates around the world and appears to be spreading. The plasmid-mediated mechanisms provide only low-level resistance that by itself does not exceed the clinical breakpoint for susceptibility but nonetheless facilitates selection of higher-level resistance and makes infection by pathogens containing PMQR harder to treat.

Genomic resistance island AGI1 carrying a complex class 1 integron in a multiply antibiotic-resistant ST25 Acinetobacter baumannii isolate

OBJECTIVES

The objective of this study was to locate the antibiotic resistance determinants in the multiply antibiotic-resistant Acinetobacter baumannii isolate D4.

METHODS

The genome was sequenced using Illumina HiSeq and assembled de novo using Velvet. PCR was used to link the relevant contigs and fill the gaps. Sequences were compared with ones in GenBank and annotated.

RESULTS

A sporadic A. baumannii isolate D4, recovered in Sydney in 2006 from a wound, was multiply antibiotic resistant. D4 is ST25 (Institut Pasteur scheme) and exhibited resistance to third-generation cephalosporins and reduced susceptibility to ciprofloxacin, as well as resistance to aminoglycosides (gentamicin, kanamycin, neomycin and tobramycin) and further older antibiotics, nalidixic acid, sulfamethoxazole, streptomycin, spectinomycin and trimethoprim. The gyrA gene has a mutation consistent with nalidixic acid resistance. The bla PER conferring cephalosporin resistance, together with the aadB, aadA13/2, aadA2, strAB and sul1 resistance genes, are located within a 29 173 bp complex class 1 integron that includes three copies of intI1, three cassette arrays and two copies of the 3'-conserved segment. This integron is adjacent to the resG gene of an integrative genomic resistance island, AGI1 (Acinetobacter genomic island 1), with a backbone related to that of islands in the SGI1, SGI2 and PGI1 families. AGI1 is located at the 3'-end of the chromosomal trmE (formerly thdF) gene.

CONCLUSIONS

AGI1 represents a new lineage of genomic resistance islands that belongs in the same broad group as members of the SGI1, SGI2 and PGI1 families. Genes conferring resistance to cephalosporins, aminoglycosides and sulphonamides are located in a complex class 1 integron within AGI1.

Molecular characterization of ISCR1-mediated blaPER-1 in a non-O1, non-O139 Vibrio cholerae strain from China

We report the detection of PER-1 extended-spectrum β-lactamase (ESBL) in a clinical non-O1, non-O139 Vibrio cholerae strain from China. ISCR1-mediated bla(PER-1) was embedded in a complex In4 family class 1 integron belonging to the lineage of Tn1696 on a conjugative IncA/C plasmid. A free 8.98-kb circular molecule present with the ISCR1-bla(PER-1)-truncated 3'-conserved sequence (CS) structure was detected in this isolate. These findings may provide insight into the mobilization of bla(PER-1).

Complete nucleotide sequence of a conjugative plasmid carrying bla(PER-1)

The nucleotide sequence of a self-transmissible plasmid pVPH1 harboring bla(PER-1) from Vibrio parahaemolyticus was determined. pVPH1 was 183,730 bp in size and shared a backbone similar to pAQU1 and pAQU2, differing mainly in an ∼40-kb multidrug resistance (MDR) region. A complex class 1 integron was identified together with ISCR1 and bla(PER-1) (ISCR1-bla(PER-1)-gst-abct-qacEΔ1-sul1), which was shown to form a circular intermediate playing an important role in the dissemination of bla(PER-1).

Molecular characteristics of carbapenem-resistant gram-negative bacteria in southern China

A total of 368 nonreplicate gram-negative bacteria with resistance to imipenem or meropenem were collected to search for carbapenemase genes, class 1 integrons, and insertion sequence with common region 1 (ISCR1). The carbapenemase genes blaIMP-4, blaKPC-2, and blaNDM-1 were found in two Enterobacteriaceae and seven Pseudomonas aeruginosa isolates, nine Klebsiella pneumoniae isolates, and seven Enterobacteriaceae and two Acinetobacter spp. isolates. The class D OXA-type carbapenemase genes blaOXA-23-like, blaOXA-24-like, blaOXA-58, and blaOXA-51-like were detected in 59 (34.9%), 2 (1.2%), 16 (9.5%), and 126 (74.6%) Acinetobacter strains. This is the first description of blaNDM-1 in Enterobacter hormaechei and Acinetobacter genomic species 13TU. Of the integrase-positive strains, 135 (90.0%) Acinetobacter spp., 22 (61.1%) P. aeruginosa, and 14 (100%) Enterobacteriaceae isolates were identified by five, ten, and four different gene cassette arrays, respectively. Three novel gene cassette arrays aadB-aadA1, dfrA25, and dfrA16-aadA2 were reported for the first time in some species. Of the ISCR1-positive strains, the nonfermentative strains (102 Acinetobacter spp. and 13 P. aeruginosa. isolates) contained the same arrangement blaPER-1-putative glutathione-S-transferase-novel type ABC transporter, and three Enterobacteriaceae isolates harbored three different arrangements. Four distinct complex class 1 integron structures were observed. The complex class 1 integron detected in New Delhi, metallo-β-lactamase (NDM-1)-producing E. hormaechei, was found to coexist in the NDM-1-carrying plasmid. Our results suggested that we should pay more attention to the strict implementation of infection control measures and active antibiotic resistance surveillance to avoid the rapid spread or outbreak of carbapenemase-producing gram-negative bacteria.

The complex genetic context of blaPER-1 flanked by miniature inverted-repeat transposable elements in Acinetobacter johnsonii

On a large plasmid of Acinetobacter johnsonii strain XBB1 from hospital sewage, bla_PER-1 and ISCR1 were found in a complex Tn402-like integron carrying an arr3-aacA4 cassette array. The integron was truncated by the same 439-bp miniature inverted-repeat transposable element (MITE) at both ends. bla_PER-1 and its complex surroundings might have been mobilized by the MITEst into an orf of unknown function, evidenced by the presence of the characteristic 5-bp direct target repeats. The same 439-bp MITEs have also been found flanking class 1 integrons carrying metallo-β-lactamases genes bla_IMP-1, bla_IMP-5 and bla_VIM-2 before but without ISCR1. Although the cassette arrays are different, integrons have always been truncated by the 439-bp MITEs at the exact same locations. The results suggested that MITEs might be able to mobilize class 1 integrons via transposition or homologous recombination and therefore represent a possible common mechanism for mobilizing antimicrobial resistance determinants.