Establishment and Evaluation of a Core Genome Multilocus Sequence Typing Scheme for Whole-Genome Sequence-Based Typing of Pseudomonas aeruginosa

Three prolonged outbreaks of metallo-β-lactamase-producing Pseudomonas aeruginosa in an Upper Austrian hospital, 2017-2023

In spring 2022, an increase in metallo-β-lactamase-producing Pseudomonas aeruginosa (MBL-Pa) infections was detected in a hospital in Upper Austria. To identify the source of infection and to stop further transmissions, an epidemiological outbreak investigation including whole-genome sequencing (WGS)-based typing was conducted. The final case definition included cases admitted to the hospital between 2020 and 2023 with an MBL-Pa in one of the three genomic clusters identified. In addition, the investigation was extended to include historical cases from 2017. Core genome multilocus sequence typing was performed to assess the genetic relatedness between the isolates. Fifty-four clinical P. aeruginosa isolates and eight P. aeruginosa isolates from the hospital environment were obtained. All but nine isolates grouped into one of three genomic clusters (ST235/blaVIM-1, ST111/blaVIM-2, or ST621/blaIMP-13), which were considered to be distinct, prolonged outbreaks involving 47 out of 52 cases. The most likely source of infection for cluster 1 (ST111/blaVIM-2) and cluster 2 (ST235/blaVIM-1) was sinks in the intensive care unit (ICU) washroom. Cluster 3 clone (ST621/blaIMP-13) could have originated in the urology ward in 2020 and then spread to the ICU years later. However, the nosocomial origin of this clone could not be proven. In March 2023, following the implementation of control measures (gowning, patient isolation, screening, and daily disinfection), no further MLB-Pa was detected, and the outbreaks were considered to be over. As ICUs play an important role in the transmission of P. aeruginosa, emphasis should be placed on genomic surveillance, infection prevention, and control in such wards.

IMPORTANCE

The significance of our work lies in the successful resolution of three prolonged outbreaks of MBL-Pa infections in a hospital in Upper Austria. Through a comprehensive epidemiological investigation coupled with WGS-based typing of P. aeruginosa isolates, the study identified three distinct genomic clusters responsible for prolonged outbreaks involving 47 cases. The investigation pinpointed sinks in the ICU washroom as the likely source of infection for two of the clusters. The study demonstrates the effectiveness of control measures such as hand hygiene, gowning, patient isolation, screening, and disinfection in stopping further transmission and bringing the outbreaks to a close. This underscores the critical role of genomic surveillance and control measures, particularly in high-risk settings like ICUs, in reducing nosocomial transmission of MBL-Pa infections.

Retrospective genome-oriented analysis reveals low transmission rate of multidrug-resistant Pseudomonas aeruginosa from contaminated toilets at a bone marrow transplant unit

BACKGROUND

Prevention of toilet-to-patient transmission of multidrug-resistant Pseudomonas aeruginosa (MDR PA) poses management-related challenges at many bone marrow transplant units (BMTUs).

AIM

To conduct a longitudinal retrospective analysis of the toilet-to-patient transmission rate for MDR PA under existing infection control (IC) measures at a BMTU with persistent MDR PA toilet colonization.

METHODS

The local IC bundle comprised: (1) patient education regarding IC; (2) routine patient screening; (3) toilet flushing volume of 9 L; (4) bromination of toilet water tanks, and (5) toilet decontamination using hydrogen peroxide. Toilet water was sampled periodically between 2016 and 2021 (minimum every three months: 26 intervals). Upon MDR PA detection, disinfection and re-sampling were repeated until ≤3 cfu/100 mL was reached. Whole-genome sequencing (WGS) was performed retrospectively on all available MDR PA isolates (90 out of 117 positive environmental samples, 10 out of 14 patients, including nine nosocomial).

FINDINGS

WGS of patient isolates identified six sequence types (STs), with ST235/CT1352/FIM-1 and ST309/CT3049/no-carbapenemase being predominant (three isolates each). Environmental sampling consistently identified MDR PA ST235 (65.5% ST235/CT1352/FIM-1), showing low genetic diversity (difference of ≤29 alleles by core-genome multi-locus sequence typing (cgMLST)). This indicates that direct toilet-to-patient transmission was infrequent although MDR PA was widespread (detection on 79 occasions, detection in every toilet). Only three MDR PA patient isolates can be attributed to the ST235/CT1352/FIM-1 toilet MRD PA population over six years.

CONCLUSION

Stringent targeted toilet disinfection can reduce the potential risk for MDR PA acquisition by patients.

Genomic and phenotypic inconsistencies in Pseudomonas aeruginosa resistome among intensive care patients

Objective

Pseudomonas aeruginosa, a difficult-to-manage nosocomial pathogen, poses a serious threat to clinical outcomes in intensive care (ICU) patients due to its high antimicrobial resistance (AMR). To promote effective management, it is essential to investigate the genomic and phenotypic differences in AMR expression of the isolates.

Methods

A prospective observational study was conducted from July 2022 to April 2023 at Liepaja Regional Hospital in Latvia. The study included all adult patients who were admitted to the ICU and had a documented infection with P. aeruginosa, as confirmed by standard laboratory microbiological testing and short-read sequencing. Since ResFinder is the only sequencing-based database offering antibacterial susceptibility testing (AST) data for each antibiotic, we conducted a comparison of the resistance profile with the results of phenotypic testing, evaluating if ResFinder met the US Food and Drug Administration (FDA) requirements for approval as a new AMR diagnostic test. Next, to improve precision, AST data from ResFinder was compared with two other databases - AMRFinderPlus and RGI. Additionally, data was gathered from environmental samples to inform the implementation of appropriate infection control measures in real time.

Results

Our cohort consisted of 33 samples from 29 ICU patients and 34 environmental samples. The presence of P. aeruginosa infection was found to be associated with unfavourable clinical outcomes. A third of the patient samples were identified as multi-drug resistant isolates. Apart from resistance against colistin, significant discrepancies were observed when phenotypic data were compared to genotypic data. For example, the aminoglycoside resistance prediction of ResFinder yielded a major errors value of 3.03% for amikacin, which was marginally above the FDA threshold. Among the three positive environmental samples, one sample exhibited multiple AMR genes similar to the patient samples in its cluster.

Conclusion

Our findings underscore the importance of utilizing a combination of diagnostic methods for the identification of resistance mechanisms, clusters, and environmental reservoirs in ICUs.

Core genome multilocus sequence typing (cgMLST) applicable to the monophyletic Klebsiella oxytoca species complex

The environmental bacterium Klebsiella oxytoca displays an alarming increase of antibiotic-resistant strains that frequently cause outbreaks in intensive care units. Due to its prevalence in the environment and opportunistic presence in humans, molecular surveillance (including resistance marker screening) and high-resolution cluster analysis are of high relevance. Furthermore, K. oxytoca previously described in studies is rather a species complex (KoSC) than a single species comprising at least six closely related species that are not easily differentiated by standard typing methods. To reach a discriminatory power high enough to identify and resolve clusters within these species, whole genome sequencing is necessary. The resolution is achievable with core genome multilocus sequence typing (cgMLST) extending typing of a few housekeeping genes to thousands of core genome genes. CgMLST is highly standardized and provides a nomenclature enabling cross laboratory reproducibility and data exchange for routine diagnostics. Here, we established a cgMLST scheme not only capable of resolving the KoSC species but also producing reliable and consistent results for published outbreaks. Our cgMLST scheme consists of 2,536 core genome and 2,693 accessory genome targets, with a percentage of good cgMLST targets of 98.31% in 880 KoSC genomes downloaded from the National Center for Biotechnology Information (NCBI). We also validated resistance markers against known resistance gene patterns and successfully linked genetic results to phenotypically confirmed toxic strains carrying the til gene cluster. In conclusion, our novel cgMLST enables highly reproducible typing of four different clinically relevant species of the KoSC and thus facilitates molecular surveillance and cluster investigations.

Automating the Illumina DNA library preparation kit for whole genome sequencing applications on the flowbot ONE liquid handler robot

Whole-genome sequencing (WGS) is currently making its transition from research tool into routine (clinical) diagnostic practice. The workflow for WGS includes the highly labor-intensive library preparations (LP), one of the most critical steps in the WGS procedure. Here, we describe the automation of the LP on the flowbot ONE robot to minimize the risk of human error and reduce hands-on time (HOT). For this, the robot was equipped, programmed, and optimized to perform the Illumina DNA Prep automatically. Results obtained from 16 LP that were performed both manually and automatically showed comparable library DNA yields (median of 1.5-fold difference), similar assembly quality values, and 100% concordance on the final core genome multilocus sequence typing results. In addition, reproducibility of results was confirmed by re-processing eight of the 16 LPs using the automated workflow. With the automated workflow, the HOT was reduced to 25 min compared to the 125 min needed when performing eight LPs using the manual workflow. The turn-around time was 170 and 200 min for the automated and manual workflow, respectively. In summary, the automated workflow on the flowbot ONE generates consistent results in terms of reliability and reproducibility, while significantly reducing HOT as compared to manual LP.

Whole-genome sequencing reveals two prolonged simultaneous outbreaks involving Pseudomonas aeruginosa high-risk strains ST111 and ST235 with resistance to quaternary ammonium compounds

OBJECTIVE

Water-bearing systems are known as frequent Pseudomonas aeruginosa (PA) outbreak sources. However, many older buildings continue to have sanitary facilities in high-risk departments such as the ICU. We present two simultaneous prolonged multi-drug-resistant (MDR) PA outbreaks detected at the ICU of a pulmonology hospital, which were resolved by whole-genome sequencing (WGS).

METHODS

Outbreak management and investigations were initiated in August 2019 after detecting two patients with nosocomial VIM-2-positive MDR PA. The investigations involved weekly patient screenings for four months and extensive environmental sampling for 15 months. All patient and environmental isolates were collected and analysed by WGS.

RESULTS

From April to September 2019, we identified 10 patients with nosocomial MDR PA, including five VIM-2-positive strains. VIM-2-positive strains were also detected in nine sink drains, two toilets, and a cleaning bucket. WGS revealed that of 16 VIM-2-positive isolates, 14 were ST111 that carried qacE, or qacEΔ1 genes, whereas 13 isolates clustered (difference of ≤11 alleles by cgMLST). OXA-2 (two toilets), and OXA-2, OXA-74, PER-1 (two patients, three toilets) qacEΔ1-positive ST235 isolates dominated among VIM-2-negative isolates. The remaining seven PA strains were ST17, ST233, ST273, ST309 and ST446. Outbreak containment was achieved by replacing U-bends, and cleaning buckets, and switching from quaternary ammonium compounds (QUATs) to oxygen-releasing disinfectant products.

CONCLUSION

Comprehension and management of two simultaneous MDR PA outbreaks involving the high-risk strains ST111 and ST235 were facilitated by precise control due to identification of different outbreak sources per strain, and by the in-silico detection of high-level QUATs resistance in all isolates.

Mutation Analysis in Regulator DNA-Binding Regions for Antimicrobial Efflux Pumps in 17,000 Pseudomonas aeruginosa Genomes

Mutations leading to upregulation of efflux pumps can produce multiple drug resistance in the pathogen Pseudomonas aeruginosa. Changes in their DNA binding regions, i.e., palindromic operators, can compromise pump depression and subsequently enhance resistance against several antibacterials and biocides. Here, we have identified (pseudo)palindromic repeats close to promoters of genes encoding 13 core drug-efflux pumps of P. aeruginosa. This framework was applied to detect mutations in these repeats in 17,292 genomes. Eighty-nine percent of isolates carried at least one mutation. Eight binary genetic properties potentially related to expression were calculated for mutations. These included palindromicity reduction, mutation type, positioning within the repeat and DNA-bending shift. High-risk ST298, ST308 and ST357 clones commonly carried four conserved mutations while ST175 and the cystic fibrosis-linked ST649 clones showed none. Remarkably, a T-to-C transition in the fourth position of the upstream repeat for mexEF-oprN was nearly exclusive of the high-risk ST111 clone. Other mutations were associated with high-risk sublineages using sample geotemporal metadata. Moreover, 1.5% of isolates carried five or more mutations suggesting they undergo an alternative program for regulation of their effluxome. Overall, P. aeruginosa shows a wide range of operator mutations with a potential effect on efflux pump expression and antibiotic resistance.

Sink Drains in a Neonatal Intensive Care Unit: A Retrospective Risk Assessment and Evaluation

Water systems in health care facilities can form reservoirs for Gram-negative bacteria. While planning a new neonatal intensive care unit (NICU), we performed a retrospective evaluation of potential risks from water-diverting systems on the existing NICU of our tertiary care University Hospital. During 2017 to 2023, we recorded nine nosocomial cluster events with bacterial pathogens in our NICU. Of these, three clusters of Gram-negative bacteria were potentially related to sink drains: A Klebsiella oxytoca, a Pseudomonas aeruginosa, and an Enterobacter hormaechei cluster were uncovered by clinical routine screening of patients and breastmilk samples. They were confirmed using whole-genome sequencing and a subsequent core genome multilocus sequence typing (cgMLST) algorithm. Our observations highlight that the implementation of sink drains in a NICU may have negative effects on patients' safety. Construction planning should concentrate on the avoidance of washbasins in patient rooms when redesigning sensitive areas such as NICUs.

Hospital sanitary facilities on wards with high antibiotic exposure play an important role in maintaining a reservoir of resistant pathogens, even over many years

BACKGROUND

Hospitals with their high antimicrobial selection pressure represent the presumably most important reservoir of multidrug-resistant human pathogens. Antibiotics administered in the course of treatment are excreted and discharged into the wastewater system. Not only in patients, but also in the sewers, antimicrobial substances exert selection pressure on existing bacteria and promote the emergence and dissemination of multidrug-resistant clones. In previous studies, two main clusters were identified in all sections of the hospital wastewater network that was investigated, one K. pneumoniae ST147 cluster encoding NDM- and OXA-48 carbapenemases and one VIM-encoding P. aeruginosa ST823 cluster. In the current study, we investigated if NDM- and OXA-48-encoding K. pneumoniae and VIM-encoding P. aeruginosa isolates recovered between 2014 and 2021 from oncological patients belonged to those same clusters.

METHODS

The 32 isolates were re-cultured, whole-genome sequenced, phenotypically tested for their antimicrobial susceptibility, and analyzed for clonality and resistance genes in silico.

RESULTS

Among these strains, 25 belonged to the two clusters that had been predominant in the wastewater, while two others belonged to a sequence-type less prominently detected in the drains of the patient rooms.

CONCLUSION

Patients constantly exposed to antibiotics can, in interaction with their persistently antibiotic-exposed sanitary facilities, form a niche that might be supportive for the emergence, the development, the dissemination, and the maintenance of certain nosocomial pathogen populations in the hospital, due to antibiotic-induced selection pressure. Technical and infection control solutions might help preventing transmission of microorganisms from the wastewater system to the patient and vice versa, particularly concerning the shower and toilet drainage. However, a major driving force might also be antibiotic induced selection pressure and parallel antimicrobial stewardship efforts could be essential.

A 10-year microbiological study of Pseudomonas aeruginosa strains revealed the circulation of populations resistant to both carbapenems and quaternary ammonium compounds

Pseudomonas aeruginosa is one of the leading causes of healthcare-associated infections. For this study, the susceptibility profiles to antipseudomonal antibiotics and a quaternary ammonium compound, didecyldimethylammonium chloride (DDAC), widely used as a disinfectant, were established for 180 selected human and environmental hospital strains isolated between 2011 and 2020. Furthermore, a genomic study determined resistome and clonal putative relatedness for 77 of them. During the ten-year study period, it was estimated that 9.5% of patients' strains were resistant to carbapenems, 11.9% were multidrug-resistant (MDR), and 0.7% were extensively drug-resistant (XDR). Decreased susceptibility (DS) to DDAC was observed for 28.0% of strains, a phenotype significantly associated with MDR/XDR profiles and from hospital environmental samples (p < 0.0001). According to genomic analyses, the P. aeruginosa population unsusceptible to carbapenems and/or to DDAC was diverse but mainly belonged to top ten high-risk clones described worldwide by del Barrio-Tofiño et al. The carbapenem resistance appeared mainly due to the production of the VIM-2 carbapenemase (39.3%) and DS to DDAC mediated by MexAB-OprM pump efflux overexpression. This study highlights the diversity of MDR/XDR populations of P. aeruginosa which are unsusceptible to compounds that are widely used in medicine and hospital disinfection and are probably distributed in hospitals worldwide.

Rapid Identification of Pseudomonas aeruginosa International High-Risk Clones Based on High-Resolution Melting Analysis

The Pseudomonas aeruginosa population has a nonclonal epidemic structure. It is generally composed of a limited number of widespread clones selected from a background of many rare and unrelated genotypes recombining at high frequency. Due to the increasing prevalence of nosocomial infections caused by multidrug-resistant/extensively drug-resistant (MDR/XDR) strains, it is advisable to implement infection control measures. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) are considered the gold standard methods in bacterial typing, despite being limited by cost, staff, and instrumental demands. Here, we present a novel mini-MLST scheme for P. aeruginosa rapid genotyping based on high-resolution melting analysis. Using the proposed mini-MLST scheme, 3,955 existing sequence types (STs) were converted into 701 melting types (MelTs), resulting in a discriminatory power of D = 0.993 (95% confidence interval [CI], 0.992 to 0.994). Whole-genome sequencing of 18 clinical isolates was performed to support the newly designed mini-MLST scheme. The clonal analysis of STs belonging to MelTs associated with international high-risk clones (HRCs) performed by goeBURST software revealed that a high proportion of the included STs are highly related to HRCs and have also been witnessed as responsible for serious infections. Therefore, mini-MLST provides a clear warning for the potential spread of P. aeruginosa clones recognized as MDR/XDR strains with possible serious outcomes. IMPORTANCE In this study, we designed a novel mini-MLST typing scheme for Pseudomonas aeruginosa. Its great discriminatory power, together with ease of performance and short processing time, makes this approach attractive for prospective typing of large isolate sets. Integrating the novel P. aeruginosa molecular typing scheme enables the development and spread of MDR/XDR high-risk clones to be investigated.

Genome-based typing reveals rare events of patient contamination with Pseudomonas aeruginosa from other patients and sink traps in a medical intensive care unit

AIM

We used genome-based typing data with the aim of identifying the routes of acquisition of Pseudomonas aeruginosa by patients hospitalized in a medical intensive care unit (MICU) over a long period in a non-epidemic context.

METHODS

This monocentric prospective study took place over 10 months in 2019 in a 15-bed MICU that applies standard precautions of hygiene. Lockable sink traps installed at all water points of use were bleach disinfected twice a week. We sampled all sink traps weekly to collect 404 P. aeruginosa environmental isolates and collected all P. aeruginosa isolates (N = 115) colonizing or infecting patients (N = 65). All isolates had their phenotypic resistance profile determined and their genome sequenced, from which we identified resistance determinants and assessed the population structure of the collection at the nucleotide level to identify events of P. aeruginosa transmission.

FINDINGS

All sink traps were positive for P. aeruginosa, each sink trap being colonized for several months by one or more clones. The combination of genomic and spatiotemporal data identified one potential event of P. aeruginosa transmission from a sink trap to a patient (1/65, 1.5%) and six events of patient cross-transmission, leading to the contamination of five patients (5/65, 7.7%). All transmitted isolates were fully susceptible to β-lactams and aminoglycosides.

CONCLUSIONS

Genome-based typing revealed the contamination of patients by P. aeruginosa originating from sink traps to be infrequent (1.5%) in an MICU with sink trap-bleaching measures, and that only 7.7% of the patients acquired P. aeruginosa originating from another patient.

Antimicrobial Resistance and Genetic Diversity of Pseudomonas aeruginosa Strains Isolated from Equine and Other Veterinary Samples

Pseudomonas aeruginosa is one of the leading causes of healthcare-associated infections in humans. This bacterium is less represented in veterinary medicine, despite causing difficult-to-treat infections due to its capacity to acquire antimicrobial resistance, produce biofilms, and persist in the environment, along with its limited number of veterinary antibiotic therapies. Here, we explored susceptibility profiles to antibiotics and to didecyldimethylammonium chloride (DDAC), a quaternary ammonium widely used as a disinfectant, in 168 P. aeruginosa strains isolated from animals, mainly Equidae. A genomic study was performed on 41 of these strains to determine their serotype, sequence type (ST), relatedness, and resistome. Overall, 7.7% of animal strains were resistant to carbapenems, 10.1% presented a multidrug-resistant (MDR) profile, and 11.3% showed decreased susceptibility (DS) to DDAC. Genomic analyses revealed that the study population was diverse, and 4.9% were ST235, which is considered the most relevant human high-risk clone worldwide. This study found P. aeruginosa populations with carbapenem resistance, multidrug resistance, and DS to DDAC in equine and canine isolates. These strains, which are not susceptible to antibiotics used in veterinary and human medicine, warrant close the setting up of a clone monitoring, based on that already in place in human medicine, in a one-health approach.

Core Genome Multilocus Sequence Typing and Antibiotic Susceptibility Prediction from Whole-Genome Sequence Data of Multidrug-Resistant Pseudomonas aeruginosa Isolates

Over the past decade, whole-genome sequencing (WGS) has overtaken traditional bacterial typing methods for studies of genetic relatedness. Further, WGS data generated during epidemiologic studies can be used in other clinically relevant bioinformatic applications, such as antibiotic resistance prediction. Using commercially available software tools, the relatedness of 38 clinical isolates of multidrug-resistant Pseudomonas aeruginosa was defined by two core genome multilocus sequence typing (cgMLST) methods, and the WGS data of each isolate was analyzed to predict antibiotic susceptibility to nine antibacterial agents. The WGS typing and resistance prediction data were compared with pulsed-field gel electrophoresis (PFGE) and phenotypic antibiotic susceptibility results, respectively. Simpson's Diversity Index and adjusted Wallace pairwise assessments of the three typing methods showed nearly identical discriminatory power. Antibiotic resistance prediction using a trained analytical pipeline examined 342 bacterial-drug combinations with an overall categorical agreement of 92.4% and very major, major, and minor error rates of 3.6, 4.1, and 4.1%, respectively. IMPORTANCE Multidrug-resistant Pseudomonas aeruginosa isolates are a serious public health concern due to their resistance to nearly all or all of the available antibiotics, including carbapenems. Utilizing molecular approaches in conjunction with antibiotic susceptibility prediction software warrants investigation for use in the clinical laboratory workflow. These molecular tools coupled with antibiotic resistance prediction tools offer the opportunity to overcome the extended turnaround time and technical challenges of phenotypic susceptibility testing.

Development and Evaluation of a Core Genome Multilocus Sequencing Typing (cgMLST) Scheme for Serratia marcescens Molecular Surveillance and Outbreak Investigations

Serratia marcescens can cause a range of severe infections and contributes to nosocomial outbreaks. Although whole-genome sequencing (WGS)-based typing is the standard method for molecular surveillance and outbreak investigation, there is no standardized analytic scheme for S. marcescens core genome multilocus sequence typing (cgMLST). Here, the development and evaluation of a S. marcescens cgMLST scheme is reported with the goal of enabling a standardized methodology and typing nomenclature. Four hundred ninety-one high-quality S. marcescens WGS data sets were extracted from public databases and-using the genomic sequence of NCBI reference strain S. marcescens Db11 (NZ_HG326223.1) as a starting point-all Db11 genes present in ≥97% data sets used to create a cgMLST scheme. The novel scheme was evaluated using WGS data from 24 outbreak investigations (n = 175 isolates) distributed over three continents. Analysis of Db11 genes within the 491 data sets identified 2,692 target genes present in ≥97% of genomes (mean, 99.1%; median, 99.9%). These genes formed the novel cgMLST scheme, covering 47.8% of nucleotides in the Db11 genome. Analyzing 175 isolates from 24 outbreaks using the novel scheme gave comparable results to previous typing efforts for both general groupings and allelic distances within clusters. In summary, a novel cgMLST scheme for S. marcescens was developed and evaluated. The scheme and its associated nomenclature will improve standardization of typing efforts for molecular surveillance and outbreak investigation, allowing better understanding of S. marcescens genomic epidemiology and facilitating interlaboratory comparisons.

Delineating Mycobacterium abscessus population structure and transmission employing high-resolution core genome multilocus sequence typing

Mycobacterium abscessus is an emerging multidrug-resistant non-tuberculous mycobacterium that causes a wide spectrum of infections and has caused several local outbreaks worldwide. To facilitate standardized prospective molecular surveillance, we established a novel core genome multilocus sequence typing (cgMLST) scheme. Whole genome sequencing data of 1991 isolates were employed to validate the scheme, re-analyze global population structure and set genetic distance thresholds for cluster detection and taxonomic identification. We confirmed and amended the nomenclature of the main dominant circulating clones and found that these also correlate well with traditional 7-loci MLST. Dominant circulating clones could be linked to a corresponding reference genome with less than 250 alleles while 99% of pairwise comparisons between epidemiologically linked isolates were below 25 alleles and 90% below 10 alleles. These thresholds can be used to guide further epidemiological investigations. Overall, the scheme will help to unravel the apparent global spread of certain clonal complexes and as yet undiscovered transmission routes.

Detection of Pseudomonas aeruginosa Serogroup G Using Real-Time PCR for Novel Target Genes Identified Through Comparative Genomics

Accurate serotyping is essential for effective infection control. Pseudomonas aeruginosa serogroup G is one of the most common serogroups found in water. Conventional serotyping methods are not standardized and have several shortcomings. Therefore, a robust method for rapidly identifying P. aeruginosa serotypes is required. This study established a real-time PCR method for identifying P. aeruginosa serogroup G strains using novel target gene primers based on comparative genomic analysis. A total of 343 genome sequences, including 16 P. aeruginosa serogroups and 67 other species, were analyzed. Target genes identified were amplified using real-time PCR for detecting P. aeruginosa serogroup G strains. Eight serogroup G genes, PA59_01276, PA59_01887, PA59_01888, PA59_01891, PA59_01894, PA59_04268, PA59_01892, and PA59_01896, were analyzed to determine specific targets. A real-time fluorescence quantitative PCR method, based on the novel target PA59_01276, was established to detect and identify serogroup G strains. The specificity of this method was confirmed using P. aeruginosa serogroups and non-P. aeruginosa species. The sensitivity of this real-time PCR method was 4 × 10² CFU/mL, and it could differentiate and detect P. aeruginosa serogroup G in the range of 4.0 × 10³–4.0 × 10⁸ CFU/mL in artificially contaminated drinking water samples without enrichment. The sensitivity of these detection limits was higher by 1–3 folds compared to that of the previously reported PCR methods. In addition, the G serum group was accurately detected using this real-time PCR method without interference by high concentrations of artificially contaminated serum groups F and D. These results indicate that this method has high sensitivity and accuracy and is promising for identifying and rapidly detecting P. aeruginosa serogroup G in water samples. Moreover, this research will contribute to the development of effective vaccines and therapies for infections caused by multidrug-resistant P. aeruginosa.

Whole Genome Sequencing, Antibiotic Resistance, and Epidemiology Features of Nontyphoidal Salmonella Isolated From Diarrheic Children: Evidence From North China

Nontyphoidal Salmonella (NTS) in children remains a growing burden on public health and often causes children to be hospitalized with diarrheic symptoms. In this work, 260 strains of human Salmonella isolated from Jilin, China were characterized by serotypes and antimicrobial resistance using whole genome sequencing (WGS). The most prevalent serotype was Salmonella enteritidis (47.3%), followed by S. I 4,[5],12:i:- (33.1%), and Salmonella Typhimurium (7.3%). Furthermore, the consistency between resistance phenotype and genotype was confirmed. Similarly, strains harbored bla_TEM−1B and tetA genes were detected, which verified the level of resistant phenotype in β-lactams and tetracyclines. The presence of a single mutation in parC, gyrA, and qnrS1 genes corresponding to quinolones was also observed. In our work, multilocus sequence typing (MLST) and core genome multilocus sequence typing (cgMLST) were found to have a high resolution to molecular traceability, and the combination of both was conducive to practical application in an actual situation. Taking all of this into account, we suggested that the comprehensive surveillance of Salmonella infection in children should be carried out to monitor antimicrobial-resistant trends from various sources and to alert on outbreaks of foodborne diseases to protect public health.

OUP accepted manuscript

Objectives

To describe the propensity of carbapenem-resistant Pseudomonas aeruginosa to spread within a hospital critical care setting.

Methods

The study was conducted in a 700-bed tertiary centre in Cologne, Germany. P. aeruginosa resistant to piperacillin, ceftazidime, cefepime, imipenem, meropenem and ciprofloxacin, isolated from clinical and screening specimens from four critical care units from 2015 to 2020 were analysed. Genotyping was carried out by WGS (Illumina and MinION). MLST, core genome MLST (cgMLST) and resistome analysis was performed and merged with epidemiological data.

Results

Fifty-five out of 79 non-duplicate P. aeruginosa isolates were available, of which 20 were carbapenemase producers as follows: bla_VIM-1 (n = 1), bla_VIM-2 (n = 17), bla_VIM-4 (n = 1), and bla_NDM-1/bla_GES-5 (n = 1). Forty-two of 55 isolates were hospital-acquired. cgMLST revealed three clusters: Cluster 1 (n = 15, ST111, bla_VIM-2, recovered between 2015 and 2020); Cluster 2 (n = 4, ST970, carbapenemase negative); and Cluster 3 (n = 2, ST357, carbapenemase negative). The bla_VIM-2 gene of Cluster 1 was integrated on the chromosome in a class 1 integron (type In59). Using conventional epidemiology, we were only able to confirm two patient-to-patient transmissions and one room-to-patient transmission on three different ICUs within Cluster 1. Isolates from Cluster 2 represented an outbreak occurring in 2019.

Conclusions

These data give insight into the epidemiology of carbapenem-resistant P. aeruginosa. Transmission dynamics differed between carbapenemase- and non-carbapenemase-producing isolates. A continuous acquisition of clonally related ST111 VIM-2 P. aeruginosa, being the main carbapenemase-producing strain, was observed over the whole study period, as well as an overall higher genomic diversity among non-carbapenemase-producing P. aeruginosa.

National surveillance pilot study unveils a multicenter, clonal outbreak of VIM-2-producing Pseudomonas aeruginosa ST111 in the Netherlands between 2015 and 2017

Verona Integron-encoded Metallo-beta-lactamase (VIM) is the most frequently-encountered carbapenemase in the healthcare-related pathogen Pseudomonas aeruginosa. In the Netherlands, a low-endemic country for antibiotic-resistant bacteria, no national surveillance data on the prevalence of carbapenemase-producing P. aeruginosa (CPPA) was available. Therefore, in 2016, a national surveillance pilot study was initiated to investigate the occurrence, molecular epidemiology, genetic characterization, and resistomes of CPPA among P. aeruginosa isolates submitted by medical microbiology laboratories (MMLs) throughout the country. From 1221 isolates included in the study, 124 (10%) produced carbapenemase (CIM-positive); of these, the majority (95, 77%) were positive for the bla_VIM gene using PCR. Sequencing was performed on 112 CIM-positive and 56 CIM-negative isolates (n = 168), and genetic clustering revealed that 75/168 (45%) isolates were highly similar. This genetic cluster, designated Group 1, comprised isolates that belonged to high-risk sequence type ST111/serotype O12, had similar resistomes, and all but two carried the bla_VIM-2 allele on an identical class 1 integron. Additionally, Group 1 isolates originated from around the country (i.e. seven provinces) and from multiple MMLs. In conclusion, the Netherlands had experienced a nationwide, inter-institutional, clonal outbreak of VIM-2-producing P. aeruginosa for at least three years, which this pilot study was crucial in identifying. A structured, national surveillance program is strongly advised to monitor the spread of Group 1 CPPA, to identify emerging clones/carbapenemase genes, and to detect transmission in and especially between hospitals in order to control current and future outbreaks.

Techniques in bacterial strain typing: past, present, and future

PURPOSE OF REVIEW

The advancement of molecular techniques such as whole-genome sequencing (WGS) has revolutionized the field of bacterial strain typing, with important implications for epidemiological surveillance and outbreak investigations. This review summarizes state-of-the-art techniques in strain typing and examines barriers faced by clinical and public health laboratories in implementing these new methodologies.

RECENT FINDINGS

WGS-based methodologies are on track to become the new 'gold standards' in bacterial strain typing, replacing traditional methods like pulsed-field gel electrophoresis and multilocus sequence typing. These new techniques have an improved ability to identify genetic relationships among organisms of interest. Further, advances in long-read sequencing approaches will likely provide a highly discriminatory tool to perform pangenome analyses and characterize relevant accessory genome elements, including mobile genetic elements carrying antibiotic resistance determinants in real time. Barriers to widespread integration of these approaches include a lack of standardized workflows and technical training.

SUMMARY

Genomic bacterial strain typing has facilitated a paradigm shift in clinical and molecular epidemiology. The increased resolution that these new techniques provide, along with epidemiological data, will facilitate the rapid identification of transmission routes with high confidence, leading to timely and effective deployment of infection control and public health interventions in outbreak settings.