Citrobacter telavivum sp. nov. with chromosomal mcr-9 from hospitalized patients

Emergence of colistin-resistant Enterobacter cloacae and Raoultella ornithinolytica carrying the phosphoethanolamine transferase gene, mcr-9, derived from vegetables in Japan

IMPORTANCE

Plasmid-mediated mobile colistin-resistance genes have been recognized as a global threat because they jeopardize the efficacy of colistin in therapeutic practice. Here, we described the genetic features of two mcr-9.1-carrying Gram-negative bacteria with a colistin-resistant phenotype derived from vegetables in Japan. The colistin-resistant mcr-9.1, which has never been detected in vegetables, was located on a large plasmid in Enterobacter cloacae CST17-2 and Raoultella ornithinolytica CST129-1, suggesting a high chance of horizontal gene transfer. To the best of our knowledge, this is the first report of mcr-9 in R. ornithinolytica. This study indicates that fresh vegetables might be a potential source for the transmission of mcr-9 genes encoding resistance to frontline (colistin) and clinically relevant antimicrobials. The study also provides additional consideration for colistin use and the relevance of routine surveillance in epidemiological perspective to curb the continuous spread of mcr alleles.

The phylogenomic landscape of extended-spectrum β-lactamase producing Citrobacter species isolated from surface water

BACKGROUND

Citrobacter species are Gram-negative opportunistic pathogens commonly reported in nosocomial-acquired infections. This study characterised four Citrobacter species that were isolated from surface water in the North West Province, South Africa.

RESULTS

Phenotypic antimicrobial susceptibility profiles of the isolates demonstrated their ability to produce the extended-spectrum β-lactamase (ESBL). Whole genomes were sequenced to profile antibiotic resistance and virulence genes, as well as mobile genetic elements. In silico taxonomic identification was conducted by using multi-locus sequence typing and average nucleotide identity. A pangenome was used to determine the phylogenomic landscape of the Citrobacter species by using 109 publicly available genomes. The strains S21 and S23 were identified as C. braakii, while strains S24 and S25 were C. murliniae and C. portucalensis, respectively. Comparative genomics and sequenced genomes of the ESBL-producing isolates consisted of n = 91; 83% Citrobacter species in which bla-CMY-101 (n = 19; 32,2%) and bla-CMY-59 (n = 12; 38,7%) were prevalent in C. braakii, and C. portucalensis strains, respectively. Macrolide (acrAB-TolC, and mdtG) and aminoglycoside (acrD) efflux pumps genes were identified in the four sequenced Citrobacter spp. isolates. The quinolone resistance gene, qnrB13, was exclusive to the C. portucalensis S25 strain. In silico analysis detected plasmid replicon types IncHI1A, IncP, and Col(VCM04) in C. murliniae S24 and C. portucalensis S25, respectively. These potentially facilitate the T4SS secretion system in Citrobacter species. In this study, the C. braakii genomes could be distinguished from C. murliniae and C. portucalensis on the basis of gene encoding for cell surface localisation of the CPS (vexC) and identification of genes involved in capsule polymer synthesis (tviB and tviE). A cluster for the salmochelin siderophore system (iro-BCDEN) was found in C. murliniae S24. This is important when it comes to the pathogenicity pathway that confers an advantage in colonisation.

CONCLUSIONS

The emerging and genomic landscapes of these ESBL-producing Citrobacter species are of significant concern due to their dissemination potential in freshwater systems. The presence of these ESBL and multidrug-resistant (MDR) pathogens in aquatic environments is of One Health importance, since they potentially impact the clinical domain, that is, in terms of human health and the agricultural domain, that is, in terms of animal health and food production as well as the environmental domain.

Comparative Genomic Analyses of Virulence and Antimicrobial Resistance in Citrobacter werkmanii, an Emerging Opportunistic Pathogen

Citrobacter werkmanii is an emerging and opportunistic human pathogen found in developing countries and is a causative agent of wound, urinary tract, and blood infections. The present study conducted comparative genomic analyses of a C. werkmanii strain collection from diverse geographical locations and sources to identify the relevant virulence and antimicrobial resistance genes. Pangenome analyses divided the examined C. werkmanii strains into five distinct clades; the subsequent classification identified genes with functional roles in carbohydrate and general metabolism for the core genome and genes with a role in secretion, adherence, and the mobilome for the shell and cloud genomes. A maximum-likelihood phylogenetic tree with a heatmap, showing the virulence and antimicrobial genes' presence or absence, demonstrated the presence of genes with functional roles in secretion systems, adherence, enterobactin, and siderophore among the strains belonging to the different clades. C. werkmanii strains in clade V, predominantly from clinical sources, harbored genes implicated in type II and type Vb secretion systems as well as multidrug resistance to aminoglycoside, beta-lactamase, fluoroquinolone, phenicol, trimethoprim, macrolides, sulfonamide, and tetracycline. In summary, these comparative genomic analyses have demonstrated highly pathogenic and multidrug-resistant genetic profiles in C. werkmanii strains, indicating a virulence potential for this commensal and opportunistic human pathogen.

First reported detection of the mobile colistin resistance genes, mcr-8 and mcr-9, in the Irish environment

The emergence and dissemination of mobile colistin resistance (mcr) genes across the globe poses a significant threat to public health, as colistin remains one of the last line treatment options for multi-drug resistant infections. Environmental samples (157 water and 157 wastewater) were collected in Ireland between 2018 and 2020. Samples collected were assessed for the presence of antimicrobial resistant bacteria using Brilliance ESBL, Brilliance CRE, mSuperCARBA and McConkey agar containing a ciprofloxacin disc. All water and integrated constructed wetland influent and effluent samples were filtered and enriched in buffered peptone water prior to culture, while wastewater samples were cultured directly. Isolates collected were identified via MALDI-TOF, were tested for susceptibility to 16 antimicrobials, including colistin, and subsequently underwent whole genome sequencing. Overall, eight mcr positive Enterobacterales (one mcr-8 and seven mcr-9) were recovered from six samples (freshwater (n = 2), healthcare facility wastewater (n = 2), wastewater treatment plant influent (n = 1) and integrated constructed wetland influent (piggery farm waste) (n = 1)). While the mcr-8 positive K. pneumoniae displayed resistance to colistin, all seven mcr-9 harbouring Enterobacterales remained susceptible. All isolates demonstrated multi-drug resistance and through whole genome sequencing analysis, were found to harbour a wide variety of antimicrobial resistance genes i.e., 30 ± 4.1 (10-61), including the carbapenemases, bla_OXA-48 (n = 2) and bla_NDM-1 (n = 1), which were harboured by three of the isolates. The mcr genes were located on IncHI2, IncFIIK and IncI1-like plasmids. The findings of this study highlight potential sources and reservoirs of mcr genes in the environment and illustrate the need for further research to gain a better understanding of the role the environment plays in the persistence and dissemination of antimicrobial resistance.

A new pathogenic isolate of Kocuria kristinae identified for the first time in the marine fish Larimichthys crocea

In recent years, new emerging pathogenic microorganisms have frequently appeared in animals, including marine fish, possibly due to climate change, anthropogenic activities, and even cross-species transmission of pathogenic microorganisms among animals or between animals and humans, which poses a serious issue for preventive medicine. In this study, a bacterium was clearly characterized among 64 isolates from the gills of diseased large yellow croaker Larimichthys crocea that were raised in marine aquaculture. This strain was identified as K. kristinae by biochemical tests with a VITEK 2.0 analysis system and 16S rRNA sequencing and named K. kristinae_LC. The potential genes that might encode virulence-factors were widely screened through sequence analysis of the whole genome of K. kristinae_LC. Many genes involved in the two-component system and drug-resistance were also annotated. In addition, 104 unique genes in K. kristinae_LC were identified by pan genome analysis with the genomes of this strain from five different origins (woodpecker, medical resource, environment, and marine sponge reef) and the analysis results demonstrated that their predicted functions might be associated with adaptation to living conditions such as higher salinity, complex marine biomes, and low temperature. A significant difference in genomic organization was found among the K. kristinae strains that might be related to their hosts living in different environments. The animal regression test for this new bacterial isolate was carried out using L. crocea, and the results showed that this bacterium could cause the death of L. crocea and that the fish mortality was dose-dependent within 5 days post infection, indicating the pathogenicity of K. kristinae_LC to marine fish. Since K. kristinae has been reported as a pathogen for humans and bovines, in our study, we revealed a new isolate of K. kristinae_LC from marine fish for the first time, suggesting the potentiality of cross-species transmission among animals or from marine animals to humans, from which we would gain insight to help in future public prevention strategies for new emerging pathogens.

Citrobacter meridianamericanus sp. nov., isolated from a soil sample

A Gram-stain-negative strain, designated BR102^T, isolated from a soil sample in Brazil was characterized by a polyphasic approach. Comparative 16S rRNA gene sequences indicated that strain BR102^T belonged to the genus Citrobacter. The recN- and whole-genome-based phylogeny, and multilocus sequence analysis based on concatenated partial fusA, leuS, pyrG and rpoB sequences strongly supported a clade encompassing strain BR102^T and a strain from public database that was distinct from currently recognized species of the genus Citrobacter. Average nucleotide identity and digital DNA-DNA hybridization values between strain BR102^T and the closest relative Citrobacter freundii ATCC 8090^T were 91.8 and 48.8 %, respectively. The ability to metabolize different compounds further discriminated strain BR102^T from other closely related species of the genus Citrobacter. The novel variants bla _CMY-179 and qnrB97, which encoded a CMY-2-like β-lactamase and a QnrB-type protein, respectively, were identified in strain BR102^T. BR102^T was resistant to ampicillin, amoxicillin/clavulanate and cefoxitin. The DNA G+C content of strain BR102^T is 51.3 mol%. Based on these results, strain BR102^T represents a novel species of the genus Citrobacter, for which the name Citrobacter meridianamericanus sp. nov. is proposed. The type strain is BR102^T (=MUM 22.55^T=IMI 507229^T).

Phylogenomic analysis of Citrobacter sp. strain AAK_AS5 and its metabolic capabilities to support nitrogen removal behavior

Despite the ubiquity of the genus Citrobacter in clinical, industrial, and environmental scenarios, a large number of Citrobacter strains have not been explored at the genome-scale level. In this study, accurate taxonomic assignment of strain AAK_AS5 isolated from activated sludge was achieved by in-silico genomic comparison using Overall Genome-based Relatedness Indices (ANI(OAT): 97.55%, ANIb:97.28%, and ANIm: 97.83%) that indicated its closest identity to the related strain Citrobacter portucalensis A60^T . Results were consistent with a digital DNA-DNA hybridization value of 80% with C. portucalensis A60^T which was greater than the species boundary value >70% for delineating closely related bacterial species. Gene mining through Kyoto Encyclopedia of Genes and Genomes (KEGG), and annotation using rapid annotation subsystem technology (RAST) revealed the notable gene contents for nitrogen metabolism and other pathways associated with nitrate/nitrite ammonification (28 genes), ammonia assimilation (22 genes), and denitrification pathways (14 genes). Furthermore, the strain AAK_AS5 also exhibited a high soluble chemical oxygen demand (sCOD), NH₄ ⁺ -N, and NO₃ ^- -N removal efficiency of 91.4%, 90%, and 93.6%, respectively thus validating its genetic capability for utilizing both (NH₄ )₂ SO₄ and KNO₃ as the nitrogen source. The study provided deeper insights into the phylogenomics and the genetic potential of Citrobacter, sp. strain AAK AS5 associated with nitrogen metabolism thus signifying the potential application of the isolate for treating nitrogen-rich wastewaters.

Update on Accepted Novel Bacterial Isolates Derived from Human Clinical Specimens and Taxonomic Revisions Published in 2020 and 2021

A number of factors, including microbiome analyses and the increased utilization of whole-genome sequencing in the clinical microbiology laboratory, has contributed to the explosion of novel prokaryotic species discovery, as well as bacterial taxonomy revision. This review attempts to summarize such changes relative to human clinical specimens that occurred in 2020 and 2021, per primary publication in the International Journal of Systematic and Evolutionary Microbiology or acceptance on Validation Lists published by the International Journal of Systematic and Evolutionary Microbiology. Of particular significance among valid and effectively published taxa within the past 2 years were novel Corynebacterium spp., coagulase-positive staphylococci, Pandoraea spp., and members of family Yersiniaceae. Noteworthy taxonomic revisions include those within the Bacillus and Lactobacillus genera, family Staphylococcaceae (including unifications of subspecies designations to species level taxa), Elizabethkingia spp., and former members of Clostridium spp. and Bacteroides spp. Revisions within the Brucella genus have the potential to cause deleterious effects unless the relevance of such changes is properly communicated by microbiologists to stakeholders in clinical practice, infection prevention, and public health.

Modified Drug-Susceptibility Testing and Screening Culture Agar for Colistin-Susceptible Enterobacteriaceae Isolates Harboring a Mobilized Colistin Resistance Gene mcr-9

Three isolates of the Enterobacter cloacae complex harboring mcr-9, a member of the colistin resistance mcr gene family encoded on plasmids, were susceptible to colistin, with MICs of 0.125 to 0.5 μg/mL in standard broth microdilution (BMD) tests using cation-adjusted Mueller-Hinton broth (CA-MHB) in accordance with European Committee on Antimicrobial Susceptibility Testing guidelines. In contrast, their MICs for colistin were significantly higher (4 to 128 μg/mL) when BMD tests were performed using brain-heart infusion (BHI) medium, Luria-Bertani (LB) broth, tryptic soy broth (TSB), or CA-MHB supplemented with casein, tryptonen or peptone. Colistin significantly induced mcr-9 expression in a dose-dependent manner when these mcr-9-positive isolates were cultured in BHI or CA-MHB supplemented with peptone/casein. Pretreatment of mcr-9-positive isolates and Escherichia coli DH5α harboring mcr-9 with colistin significantly increased their survival rates against LL-37, a human antimicrobial peptide. Electrospray ionization time-of-flight mass spectrometry analysis showed that a lipid A moiety of lipopolysaccharide was partially modified by phosphoethanolamine in E. coli DH5α harboring mcr-9 when treated with colistin. Of 93 clinical isolates of Enterobacteriaceae, only the mcr-9-positive isolates showed MICs to colistin that were at least 32 times higher in BHI than in CA-MHB. These mcr-9-positive isolates grew on a modified BHI agar, MCR9-JU, containing 3 μg/mL colistin. These results suggest that the BMD method using BHI is useful when performed together with the BMD method using CA-MHB to detect mcr-9-positive isolates and that MCR9-JU agar is useful in screening for Enterobacteriaceae isolates harboring mcr-9 and other colistin-resistant isolates.

Molecular antibiotic resistance mechanisms and co-transmission of the mcr-9 and metallo-β-lactamase genes in carbapenem-resistant Enterobacter cloacae complex

Carbapenem-resistant Enterobacter cloacae complex (CRECC) has increasingly emerged as a major cause of healthcare-associated infections, with colistin being one of the last-resort antibiotics of treatment. Mobile colistin resistance (mcr)-9 is a member of a growing family of mcr genes and has been reported to be an inducible gene encoding an acquired phosphoethanolamine transferase. Here, we collected 24 ECC strains from Chongqing, China from 2018 to 2021. Subsequently, antibiotic resistance genes and the transmission dynamics of the strains were determined by PCR, whole-genome sequencing, and bioinformatic analysis. The mcr-9 was identified in IncHI2/2A or IncHI2/2A + IncN plasmids from six CRECC strains and was co-located with bla NDM-1 or bla IMP-4 in 2/6 plasmids. The genetic environment of mcr-9.1 was composed of IS903B-mcr-9.1-wbuC-IS26 in the five mcr-9.1-harboring-plasmid, but IS1B was located downstream of mcr-9.2 in the pECL414-1 sequence. We also found that the pNDM-068001 plasmid carrying mcr-9.1 could be a hybrid plasmid, formed by a Tn6360-like bla NDM-1 region inserted into an mcr-9.1-positive IncHI2/2A plasmid. A conjugation assay showed that plasmids mediated the co-dissemination of mcr-9 and metallo-β-lactamase (MBL) genes. In addition, we performed induction assays with sub-inhibitory concentrations of colistin and found an increase in the relative expression levels of the mcr-9.2, qseC, and qseB genes, as well as an increase in the minimum inhibitory concentration values of colistin in the CRECC414 strain. These findings provide a basis for studying the regulatory mechanisms of mcr-9 expression and highlight the importance of effective monitoring to assess the prevalence of MBL and mcr-9 co-existing plasmids.

Chromosomal coharboring of blaIMP-60 and mcr-9 in Enterobacter asburiae isolated from a Japanese woman with empyema: a case report

BACKGROUND

Polymyxin E (colistin) is a last-resort antibiotic to treat infections caused by carbapenemase-producing Enterobacteriaceae (CPE). However, reports of CPEs resistant to colistin have been increasing, and the mcr genes are emerging as resistance mechanisms. Among them, plasmid-mediate mcr-9 is known to be associated with colistin resistance, whereas reports on chromosomal mcr-9 and its association with colistin resistance in humans are few.

CASE PRESENTATION

We identified Enterobacter asburiae harboring mcr-9 and bla_IMP-60 in the pleural fluid of a patient with empyema. The long-read sequencing technique revealed that these genes were located on its chromosome. Despite the lack of exposure to colistin, the organism showed microcolonies in the inhibition circle in the E-test and disk diffusion test. Antibiotic susceptibility testing by broth microdilution confirmed its resistance to colistin.

CONCLUSION

Our case report showed that mcr-9 can be present not only on plasmids but also on the chromosome in E. asburiae, and that the presence of mcr-9 on its chromosome may influence its susceptibility to colistin.

Global epidemiology, genetic environment, risk factors and therapeutic prospects of mcr genes: A current and emerging update

Background

Mobile colistin resistance (mcr) genes modify Lipid A molecules of the lipopolysaccharide, changing the overall charge of the outer membrane.

Results and discussion

Ten mcr genes have been described to date within eleven Enterobacteriaceae species, with Escherichia coli, Klebsiella pneumoniae, and Salmonella species being the most predominant. They are present worldwide in 72 countries, with animal specimens currently having the highest incidence, due to the use of colistin in poultry for promoting growth and treating intestinal infections. The wide dissemination of mcr from food animals to meat, manure, the environment, and wastewater samples has increased the risk of transmission to humans via foodborne and vector-borne routes. The stability and spread of mcr genes were mediated by mobile genetic elements such as the IncHI₂ conjugative plasmid, which is associated with multiple mcr genes and other antibiotic resistance genes. The cost of acquiring mcr is reduced by compensatory adaptation mechanisms. MCR proteins are well conserved structurally and via enzymatic action. Thus, therapeutics found effective against MCR-1 should be tested against the remaining MCR proteins.

Conclusion

The dissemination of mcr genes into the clinical setting, is threatening public health by limiting therapeutics options available. Combination therapies are a promising option for managing and treating colistin-resistant Enterobacteriaceae infections whilst reducing the toxic effects of colistin.

Complete Genome Sequence of Hafnia paralvei Isolate AVS0177, Harboring mcr-9 on a Plasmid

Here, we report the complete genome sequence of a Hafnia paralvei strain isolated from a lake in Switzerland in 2020. The genome consists of a 4.7-Mbp chromosome, a large plasmid (213 kb) harboring mcr-9, and a small plasmid (6 kb).

Emergence of IncHI2 Plasmids With Mobilized Colistin Resistance (mcr)-9 Gene in ESBL-Producing, Multidrug-Resistant Salmonella Typhimurium and Its Monophasic Variant ST34 From Food-Producing Animals in Italy

A collection of 177 genomes of Salmonella Typhimurium and its monophasic variant isolated in 2014-2019 from Italian poultry/livestock (n = 165) and foodstuff (n = 12), previously screened for antimicrobial susceptibility and assigned to ST34 and single-locus variants, were studied in-depth to check the presence of the novel mcr-9 gene and to investigate their genetic relatedness by whole genome sequencing (WGS). The study of accessory resistance genes revealed the presence of mcr-9.1 in 11 ST34 isolates, displaying elevated colistin minimum inhibitory concentration values up to 2 mg/L and also a multidrug-resistant (MDR) profile toward up to seven antimicrobial classes. Five of them were also extended-spectrum beta-lactamases producers (bla SHV - 12 type), mediated by the corresponding antimicrobial resistance (AMR) accessory genes. All mcr-9-positive isolates harbored IncHI2-ST1 plasmids. From the results of the Mash analysis performed on all 177 genomes, the 11 mcr-9-positive isolates fell together in the same subcluster and were all closely related. This subcluster included also two mcr-9-negative isolates, and other eight mcr-9-negative ST34 isolates were present within the same parental branch. All the 21 isolates within this branch presented an IncHI2/2A plasmid and a similar MDR gene pattern. In three representative mcr-9-positive isolates, mcr-9 was demonstrated to be located on different IncHI2/IncHI2A large-size (∼277-297 kb) plasmids, using a combined Illumina-Oxford Nanopore WGS approach. These plasmids were also compared by BLAST analysis with publicly available IncHI2 plasmid sequences harboring mcr-9. In our plasmids, mcr-9 was located in a ∼30-kb region lacking different genetic elements of the typical core structure of mcr-9 cassettes. In this region were also identified different genes involved in heavy metal metabolism. Our results underline how genomics and WGS-based surveillance are increasingly indispensable to achieve better insights into the genetic environment and features of plasmid-mediated AMR, as in the case of such IncHI2 plasmids harboring other MDR genes beside mcr-9, that can be transferred horizontally also to other major Salmonella serovars spreading along the food chain.

Silent spread of mobile colistin resistance gene mcr-9.1 on IncHI2 'superplasmids' in clinical carbapenem-resistant Enterobacterales

OBJECTIVES

mcr-9.1 is a newly described mobile colistin resistance gene. We have noted its presence in multiple species of carbapenem-resistant Enterobacterales (CRE) from our institution. We aimed to determine the clinical features, genomic context and phenotypic impact of mcr-9.1 carriage in a series of patients between 2010 and 2019.

METHODS

We identified 32 patients with mcr-9.1-carrying CRE isolates (mCRE) and collected demographic, antimicrobial exposure and infection data. Whole-genome sequencing (including short and long reads) was performed on 32 isolates. We assessed sequence similarity of mcr-9.1-harbouring plasmids, then compared our findings with plasmids for which sequence data were publicly available.

RESULTS

There was no colistin exposure in patients prior to isolation of mCRE. mcr-9.1 was identified on IncHI2 plasmids across four different bacterial species and was co-located with bla_IMP-4 in 23/30 plasmids studied. mCRE isolates did not demonstrate phenotypic colistin resistance, either at baseline or following sublethal colistin exposure, thus showing that mcr-9.1 alone is not sufficient for resistance. Publicly available sequence data indicated the presence of carbapenemase genes in 236/619 mcr-9.1-carrying genomes (38%). IncHI2 plasmids carrying mcr-9.1 and carbapenemase genes were detected in genomes from North America, Europe, North Africa, Asia and Oceania.

CONCLUSIONS

Spread of mcr-9.1 in CRE from our institution was driven by IncHI2 'superplasmids', so termed because of their large size and their prolific carriage of resistance determinants. These were also detected in global CRE genomes. Phenotypic colistin resistance was not detected in our isolates but remains to be determined from global mCRE.

Colistin-resistant Enterobacter kobei carrying mcr-9.1 and blaCTX-M-15 infecting a critically endangered franciscana dolphin (Pontoporia blainvillei), Brazil

The emergence of mobile mcr genes mediating resistance to colistin is a critical public health issue that has hindered the treatment of serious infections caused by multidrug-resistant pathogens in humans and other animals. We report the emergence of the mcr-9.1 gene in a polymyxin-resistant extended-spectrum β-lactamase (ESBL)-producing Enterobacter kobei infecting a free-living franciscana dolphin (Pontoporia blainvillei), threatened with extinction in South America. Genomic analysis confirmed the presence of genes conferring resistance to clinically relevant β-lactam [bla_CTX-M-15 , bla_ACT-9 , bla_OXA-1 and bla_TEM-1B ], aminoglycoside [aac(3)-IIa, aadA1, aph(3'')-Ib and aph(6)-Id], trimethoprim [dfrA14], tetracycline [tetA], quinolone [aac(6')-Ib-cr and qnrB1], fosfomycin [fosA], sulphonamide [sul2] and phenicol [catA1 and catB3] antibiotics. The identification of mcr-9.1 in a CTX-M-15-producing pathogen infecting a critically endangered animal is of serious concern, which should be interpreted as a sign of further spread of critical priority pathogens and their resistance genes in threatened ecosystems.