Biology subjects

Passet, V.

Publications and source records attributed to Passet, V..

18 recordsLinked to original sources

bioRxiv2026

Modified Elek test improves in-vitro detection of diphtheria toxin

PurposeDiphtheria is caused by toxigenic strains of the Corynebacterium diphtheriae complex, mainly Corynebacterium diphtheriae and C. ulcerans. The diagnosis of diphtheria relies on detecting the diphtheria toxin (DT), for which Englers method of Eleks immunoprecipitation test is the gold standard. A recent optimization of Englers method was proposed by Melnikov and colleagues, showing higher sensitivity for C. ulcerans. The goal of our study was to test and adapt this optimized method, and to re-analyze apparent non-toxigenic tox gene bearing (NTTB) isolates from our collection. MethodsWe included 48 C. ulcerans, C. ramonii and C. diphtheriae isolates previously categorized as NTTB but for which no genetic explanation was found for the lack of DT expression. DT production was tested using Melnikovs method with further modifications made by us: i) increasing the antitoxin concentration; ii) using 5{degrees}C as the incubation temperature after 24h; and iii) modifying the layout of control and test strains on agar plates. Results35 of 38 C. ulcerans, 3 C. ramonii and 8 of 10 C. diphtheriae were found to be toxigenic. No genetic explanation was found regarding two non-toxigenic isolates (1 C. diphtheriae and 1 C. ulcerans), whereas for one C. diphtheriae, IS1132 was detected upstream of the tox gene. ConclusionOur modified implementation of Melnikovs Elek test improved our ability to detect diphtheria toxin production. Most isolates previously considered as NTTB but with no genetic explanation, were shown to be toxigenic using the novel method.

microbiology↗

bioRxiv2025

Pangenome structure and ecological adaptation in the Klebsiella pneumoniae species complex: insights from a geographically and time limited multi-habitat study

Klebsiella pneumoniae species complex (KpSC) members inhabit distinct ecological habitats, yet the diversity and adaptation of environmental KpSC populations remain underexplored. We investigated KpSC transmission, pangenome structure and diversity, and functional gene enrichment across four distinct habitats in Burgundy, France over one year. In total, 664 environmental samples were collected from an organic vegetable farm (n=329), an organic cattle farm (n=304) and wastewater treatment plants (WWTP; n=31), alongside 47 clinical isolates. KpSC was detected in 22.4% of environmental samples, most commonly in WWTP (83.9%), followed by vegetable farm (27.1%) and cattle farm (11.2%). A total of 336 isolates were collected and whole-genome sequenced. K. pneumoniae sensu stricto (phylogroup Kp1) was predominant (76%), followed by K. variicola subsp. variicola (phylogroup Kp3) (21%). Genomic analyses revealed substantial novel diversity, especially in environmental habitats (67 novel STs), with limited cross transmission but clear local persistence. Over 90% of environmental isolates lacked acquired antimicrobial resistance genes, whereas half of the clinical isolates exhibited a multi-drug resistance profile. Comparative pangenome analyses showed Kp1 possessed a larger and more diverse pangenome than Kp3. Human-associated populations (clinical and WWTP) shared similar pangenome structures, although clinical isolates exhibited an expanded accessory genome. Cattle farm isolates had the most restricted and distinct pangenome while vegetable farm isolates displayed the largest total genomic repertoire. Functional enrichment analysis highlighted Kp3s environmental adaptation via conserved functions linked to the phylogroup genetic background, such as metabolic and regulatory pathways, including nitrogen fixation genes. Contrarily, human-associated populations, especially Kp1 members, were enriched in acquired functions linked to the ecological context, including antimicrobial and metal resistance determinants and mobile genetic elements. These findings emphasize phylogroup- and ecological niche-driven pangenome contrasts in KpSC, contributing to explain the successful adaptation of Kp1 to multiple habitats, including human-related settings.

genomics↗

bioRxiv2024

Accurate genotyping of three major respiratory bacterial pathogens with ONT R10.4.1 long-read sequencing

High-throughput massive parallel sequencing has significantly improved bacterial pathogen genomics, diagnostics, and epidemiology. Despite its high accuracy, short-read sequencing struggles with complete genome reconstruction and assembly of extrachromosomal elements such as plasmids. Long-read sequencing with Oxford Nanopore Technologies (ONT) presents an alternative that offers benefits like real-time sequencing and cost-efficiency, particularly useful in resource-limited settings. However, the higher error rates of ONT have so far limited its application in high-precision genomic typing. The recent release of ONTs R10.4.1 chemistry, with significantly improved raw read accuracy (Q20+), offers a potential solution to this problem. The aim of this study was to evaluate the performance of ONTs latest chemistry for bacterial genomic typing against the gold standard Illumina technology, focusing on three respiratory pathogens of public health importance, Klebsiella pneumoniae, Bordetella pertussis, and Corynebacterium diphtheriae, and their related species. Using the Rapid Barcoding Kit V14, we generated and analyzed genome assemblies with different basecalling tools and models, at different simulated depths of coverage. ONT assemblies were compared to the Illumina reference for completeness and core genome multilocus sequence typing (cgMLST) accuracy (number of allelic mismatches). Our results show that genomes obtained from raw data basecalled with Dorado (with both simplex and duplex reads) SUP v0.7.1, assembled with Flye, and with a minimum coverage depth of 30x, optimized the accuracy for all bacterial species tested. The error rates were consistently below 1% of each cgMLST scheme, indicating that ONT R10.4.1 data is suitable for high-resolution genomic typing applied to outbreak investigations and public health surveillance.

genomics↗

bioRxiv2024

Genomic Epidemiology and Microevolution of the Zoonotic Pathogen Corynebacterium ulcerans

Corynebacterium ulcerans is an emerging zoonotic pathogen that belongs to the Corynebacterium diphtheriae (Cd) species complex (CdSC), and that causes diphtheria-like infections in humans. Our understanding of the transmission, phylogeography and evolution of C. ulcerans remains limited, in part due to the lack of a standardized genomic epidemiology toolkit. The aim of this work was to develop a core genome multi-locus sequence typing (cgMLST) scheme for high-resolution genotyping and classification of C. ulcerans strains, and to explore transmission, spatial spread and genomic evolution among 582 C. ulcerans isolates from sporadic clinical cases and reported case clusters. The cgMLST scheme combines 1,628 loci with highly reproducible allele calls and shows high strain subtyping resolution. We demonstrate its utility for capturing population structure by defining sublineages (SL, maximum 940 allele differences) and clonal groups (CG, 194 allele differences, AD) and for epidemiological surveillance by defining genetic clusters, i.e., previously undetected chains of transmission (25 AD). Genetic clusters correspond to cryptic and case clusters that were associated with specific geographical regions within France. Major C. ulcerans sublineages (SL325, SL331, SL339) and clonal groups (CG325, CG331, CG583) showed strong associations with diphtheria toxin variants and tox-carrying prophages or other genetic elements. The evolutionary dynamics of tox gene presence or absence varied sharply among clonal groups. The cgMLST scheme is publicly available (https://bigsdb.pasteur.fr/diphtheria) and provides a common framework for investigating the ecology, evolution and variations in virulence among C. ulcerans strains. The implementation of a standardized high-resolution genotyping method will also facilitate the tracing of C. ulcerans transmission and spread across hosts and from local to global spatial scales.

microbiology↗

bioRxiv2024

Bacterial strain nomenclature in the genomic era: Life Identification Numbers using a gene-by-gene approach

Unified strain taxonomies are needed for the epidemiological surveillance of bacterial pathogens and international communication in microbiological research. Core genome multilocus sequence typing (cgMLST) holds great promise for standardized high-resolution strain genotyping. However, this approach faces challenges including classification instability and disconnection of new nomenclature from widely adopted classical MLST identifiers. This essay discusses the cgMLST-based Life Identification Number (LIN) method, recently proposed as a stable multilevel strain taxonomy system applicable to most bacterial pathogens. We describe how LIN codes are implemented and used in practice for precise strain definitions and epidemiological tracking. Glossary Multilocus sequence typing (MLST)A genotyping method applied mostly to microbial strains to study population structure and epidemiology, based on comparing the nucleotide sequences of a small number (typically seven) of housekeeping protein-coding genes. In MLST, allele numbers are assigned to each sequence variant (allele) of a given gene. The MLST genotype of a bacterial strain is defined by the combination of the allele numbers observed at the genes that are included in the genotyping scheme. A sequence type (ST) is assigned to each unique combination of alleles, called an MLST profile. MLST was invented in 1998 and became a de-facto standard taxonomy of bacterial strains, albeit at low resolution. Core genome MLSTAn extension of MLST that analyzes sequence variation across hundreds to thousands of conserved (core) genes, shared by all strains of a species, providing higher resolution typing for genomic epidemiology and evolutionary studies. cgMLST schemes typically comprise 2000 to 4000 genes, depending on the genome size and genetic variation (in terms of presence/absence of genes) within bacterial species. A core genome sequence type (cgST) can be assigned to unique cgMLST profiles, i.e., a unique combination of cgMLST allelic numbers. Whole Genome Sequencing (WGS)A method that determines the complete DNA sequence of an organisms genome in a single process, providing comprehensive information for comparative genetic analyses based on cgMLST or other analytic methods. Single Nucleotide Polymorphisms (SNPs)Variations at a single base position in the DNA sequence among individuals isolates, strains or species, used as genetic markers for studying for example, evolutionary relationships or strain identity. Average nucleotide identity (ANI)A measure of genomic similarity between two organisms, calculated as the average percentage of identical nucleotides in orthologous genomic regions; commonly used to assess species-level relatedness in prokaryotes. TaxonomyHere, we apply the word taxonomy to bacterial strains as a system of classifying, naming and identifying strains based on shared genetic characteristics as defined by e.g., cgMLST.

microbiology↗

bioRxiv2023

A validated pangenome-scale metabolic model for the Klebsiella pneumoniae species complex

The Klebsiella pneumoniae Species Complex (KpSC) is a major source of nosocomial infections globally with high rates of resistance to antimicrobials. Consequently, there is growing interest in understanding virulence factors and their association with cellular metabolic processes for developing novel anti-KpSC therapeutics. Phenotypic assays have revealed metabolic diversity within the KpSC, but metabolism research has been neglected due to experiments being difficult and cost-intensive. Genome-scale metabolic models (GSMMs) represent a rapid and scalable in silico approach for exploring metabolic diversity, which compiles genomic and biochemical data to reconstruct the metabolic network of an organism. Here we use a diverse collection of 507 KpSC isolates, including representatives of globally distributed clinically-relevant lineages, to construct the most comprehensive KpSC pan-metabolic model to-date, KpSC pan v2. Candidate metabolic reactions were identified using gene orthology to known metabolic genes, prior to manual curation via extensive literature and database searches. The final model comprised a total of 3,550 reactions, 2,403 genes and can simulate growth on 360 unique substrates. We used KpSC pan v2 as a reference to derive strain-specific GSMMs for all 507 KpSC isolates, and compared these to GSMMs generated using a prior KpSC pan-reference (KpSC pan v1) and two single-strain references. We show that KpSC pan v2 includes a greater proportion of accessory reactions (8.8%) than KpSC pan v1 (2.5%). GSMMs derived from KpSC pan v2 also result in more accuracy growth predictions than those derived from other references in both aerobic (median accuracy = 95.4%) and anaerobic (median accuracy = 78.8%). KpSC pan v2 also generates more accurate growth predictions, with high median accuracies of 95.4% (aerobic, n=37 isolates) and 78.8% (anaerobic, n=36 isolates) for 124 matched carbon substrates. KpSC pan v2 is freely available at https://github.com/kelwyres/KpSC-pan-metabolic-model, representing a valuable resource for the scientific community, both as a source of curated metabolic information and as a reference to derive accurate strain-specific GSMMs. The latter can be used to investigate the relationship between KpSC metabolism and traits of interest, such as reservoirs, epidemiology, drug resistance or virulence, and ultimately to inform novel KpSC control strategies. Significance as a BioResource to the communityKlebsiella pneumoniae and its close relatives in the K. pneumoniae Species Complex (KpSC) are priority antimicrobial resistant pathogens that exhibit extensive genomic diversity. There is growing interest in understanding KpSC metabolism, and genome scale metabolic models (GSMMs) provide a rapid, scalable option for exploration of whole cell metabolism plus phenotype prediction. Here we present a KpSC pan-metabolic model representing the cellular metabolism of 507 diverse KpSC isolates. Our model is the largest and most comprehensive of its kind, comprising >2,400 genes associated with >3,500 metabolic reactions, plus manually curated evidence annotations. These data alone represent a key knowledge resource for the Klebsiella research community; however, our models greatest impact lies in its potential for use as a reference from which highly accurate strain-specific GSMMs can be derived to inform in depth strain-specific and/or large-scale comparative analyses. Data summaryO_LIKlebsiella pneumoniae species complex (KpSC) pan v2 metabolic model available at https://github.com/kelwyres/KpSC-pan-metabolic-model. C_LIO_LIAll KpSC isolate whole genome sequences used in this work were reported previously and are available under Bioprojects PRJEB6891, PRJNA351909, PRJNA493667, PRJNA768294, PRJNA253462, PRJNA292902 and PRJNA391323. Individual accessions listed in Table S1. C_LIO_LIStrain-specific GSMMs used for comparative analyses (deposited in Figshare - 10.6084/m9.figshare.24871914), plus their associated MEMOTE reports (indicates completeness and annotation quality), reaction and gene presence-absence matrices across all isolates. C_LIO_LIGrowth phenotype predictions derived from strain-specific GSMMs are available in Table S4. C_LIO_LIBinarised Biolog growth phenotype data for n=37 isolates (plates PM1 and PM2, aerobic and anaerobic conditions) are available in Tables S6 & S7. C_LIO_LIAdditional growth assay data for six substrates not included on Biolog plates PM1 and PM2 (deposited in Figshare - 10.6084/m9.figshare.24871914). C_LI

genomics↗

bioRxiv2023

A global Corynebacterium diphtheriae genomic framework sheds light on current diphtheria reemergence

BackgroundDiphtheria, caused by Corynebacterium diphtheriae, reemerges in Europe since 2022. Genomic sequencing can inform on transmission routes and genotypes of concern, but currently, no standard approach exists to detect clinically important genomic features and to interpret emergence in the global C. diphtheriae population framework. MethodsWe developed the bioinformatics pipeline DIPHTOSCAN (available at https://gitlab.pasteur.fr/BEBP/diphtoscan) to extract from genomes of Corynebacteria of the diphtheriae species complex, medically relevant features including tox gene presence and disruption. We analyzed 101 human C. diphtheriae isolates collected in 2022 in metropolitan and overseas France (France-2022). To define the population background of this emergence, we sequenced 379 additional isolates (mainly from France, 2018-2021) and collated 870 publicly-available genomes. ResultsThe France-2022 isolates comprised 45 tox-positive (44 toxigenic) isolates, mostly imported, belonging to 10 sublineages (<500 distinct core genes). The global dataset comprised 245 sublineages and 33.9% tox- positive genomes, with DIPHTOSCAN predicting non-toxigenicity in 16.0% of these. 12% of the global isolates, and 43.6% of France-2022 ones, were multidrug resistant. Convergence of toxigenicity with penicillin and erythromycin resistance was observed in 2 isolates from France-2022. Phylogenetic lineages Gravis and Mitis contrasted strikingly in their pathogenicity-associated genes. ConclusionsThis work provides a bioinformatics tool and global population framework to analyze C. diphtheriae genomes, revealing important heterogeneities in virulence and resistance features. Emerging genotypes combining toxigenicity and first-line antimicrobial resistance represent novel threats. Genomic epidemiology studies of C. diphtheriae should be intensified globally to improve understanding of reemergence and spatial spread.

microbiology↗

bioRxiv2022

Genomic epidemiology of Corynebacterium diphtheriae in New Caledonia

ObjectivesAn increasing number of isolations of Corynebacterium diphtheriae has been observed in recent years in the archipelago of New Caledonia. We aimed to analyze the clinical and microbiological features of samples with C. diphtheriae. MethodsAll C. diphtheriae isolates identified in New Caledonia from May 2015 to May 2019 were included. For each case, a retrospective consultation of the patient files was conducted. Antimicrobial susceptibility phenotypes, tox gene and diphtheria toxin expression, biovar and the genomic sequence were determined. Core genome multilocus sequence typing (cgMLST), 7-gene MLST and search of genes of interest were performed from genomic assemblies. Results58 isolates were included, with a median age of patients of 28 years (range: 9 days to 78 years). Cutaneous origin accounted for 51 of 58 (87.9%) isolates, and C. diphtheriae was associated with Staphylococcus aureus and/or Streptococcus pyogenes in three quarters of cases. Half of cases came either from the main city Noumea (24%, 14/58) or from the sparsely populated island of Lifou (26%, 15/58). Six tox-positive isolates were identified, associated with recent travel to Vanuatu; 5 of these cases were linked and cgMLST confirmed recent transmission. Two cases of endocarditis in young female patients with a history of rheumatic fever involved tox-negative isolates. The 58 isolates were mostly susceptible to commonly used antibiotics. In particular, no isolate was resistant to the first-line molecules amoxicillin or erythromycin. Resistance to tetracycline was found in a genomic cluster of 17 (29%) isolates, 16 of which carried the tetO gene. There were 13 cgMLST sublineages, most of which were also observed in the neighboring country Australia. ConclusionsCutaneous infections may harbor non-toxigenic C. diphtheriae isolates, which circulate largely silently in non-specific wounds. The possible introduction of tox-positive strains from a neighboring island illustrates that diphtheria surveillance should be maintained in New Caledonia, and that immunization in neighboring islands must be improved. Genomic sequencing uncovers how genotypes circulate locally and across neighboring countries.

microbiology↗

bioRxiv2022

Phages against non-capsulated Klebsiella pneumoniae: broader host range, slower resistance

BackgroundKlebsiella pneumoniae (Kp) is an ecologically generalist bacterium but also an opportunistic pathogen responsible for hospital-acquired infections and a major contributor to the global burden of antimicrobial resistance. In the last decades, few advances have been made in the use of virulent phages as alternative or complement to antibiotics to treat Kp infections. The efficiency of phages relies on their ability to recognize and attach to the bacterial surface structure, and in the case of Kp, capsule (K) is the main surface structure. However, Kp capsule is highly polymorphic and the majority of classically isolated phages are specific for unique K-types, limiting therapy prospects. In this study, we demonstrate the feasibility of an innovative strategy consisting in isolating phages that target capsule-deficient mutant Kp strains, and compare such phages with anti-capsulated cells phages phylogenetically and through in vitro and in vivo experiments. MethodsWe isolated 27 phages using 7 capsule-deficient Kp strains as hosts (anti-Kd phages), and 41 phages against 7 wild-type (wt) Kp strains (anti-K phages). We evaluated and compared phenotypically and genotypically their host range, resistance emergence and selected mutations and in-vivo activity. ResultsIn vitro, anti-Kd phages showed a broader host-range, with most phages being able to infect non-capsulated mutants of multiple sublineages and O-antigen locus types. Besides, the emergence of bacterial subpopulations non-susceptible to anti-Kd phages was slower when compared to anti-K phages and with a different range of genomic differences. One anti-Kd phage (mtp5) was shown to infect non-capsulated Kp strains belonging to 10 of the 12 known O-antigen types. Moreover, this phage was able to replicate in the gut of mice colonised with the wt (capsulated) parent strain. ConclusionsThis work demonstrates the potential value of an anti-Klebsiella phage isolation strategy that addresses the issue of narrow host-range of anti-K phages. Anti Kd-phages may be active in infection sites where capsule expression is intermittent or repressed, or in combination with anti-K phages, which often induce loss of capsule escape mutants.

microbiology↗

bioRxiv2021

Genomic evolution of the globally disseminated multidrug-resistant Klebsiella pneumoniae clonal group 147

BackgroundThe rapid emergence of multidrug-resistant Klebsiella pneumoniae (Kp) is largely driven by the spread of specific clonal groups (CG). Of these, CG147 includes 7-gene MLST sequence types ST147, ST273 and ST392. CG147 has caused nosocomial outbreaks across the world, but its global population dynamics remain unknown. Here, we report a pandrug-resistant ST147 clinical isolate from India (strain DJ) and define the evolution and global emergence of CG147. MethodsAntimicrobial susceptibility testing (EUCAST guidelines) and genome sequencing (Illumina and Oxford Nanopore technologies, Unicycler assembly) were performed on strain DJ. Additionally, we collated 217 publicly available CG147 genomes (NCBI, May 2019). CG147 evolution was inferred within a temporal phylogenetic framework (BEAST) based on a recombination-free sequence alignment (Roary/Gubbins). Comparative genomic analyses focused on resistance and virulence genes and other genetic elements (BIGSdb, Kleborate, PlasmidFinder, PHASTER, ICEFinder and CRISPRCasFinder). ResultsStrain DJ had a pandrug resistance phenotype. Its genome comprised 7 plasmids and 1 linear phage-plasmid. Four carbapenemase genes were detected: blaNDM-5 and 2 copies of blaOXA-181 in the chromosome, and a second copy of blaNDM-5 on an 84 kb IncFII plasmid. CG147 genomes carried a mean of 13 acquired resistance genes or mutations; 63% carried a carbapenemase gene and 83% harbored blaCTX-M. All CG147 genomes presented GyrA and ParC mutations and a common subtype IV-E CRISPR-Cas system. ST392 and ST273 emerged in 2005 and 1995, respectively. ST147, the most represented phylogenetic branch, was itself divided into two main clades with distinct capsular loci: KL64 (74%, DJ included, emerged in 1994 and disseminated worldwide, with carbapenemases varying among world regions) and KL10 (20%, 2002, predominantly found in Asian countries, associated with carbapenemases NDM and OXA-48-like). Further, subclades within ST147-KL64 differed in the yersiniabactin locus, OmpK35/K36 mutations, plasmid replicons and prophages. The absence of IncF plasmids in some subclades was associated with a possible activity of a CRISPR-Cas system. ConclusionsK. pneumoniae clonal group CG147 comprises pandrug- or extensively-resistant isolates and carries multiple and diverse resistance genes and mobile genetic elements, including chromosomal blaNDM-5. Its emergence is driven by the spread of several phylogenetic clades marked by their own genomic features and specific temporo-spatial dynamics. These findings highlight the need for precision surveillance strategies to limit the spread of particularly concerning CG147 subsets.

genomics↗

bioRxiv2021

Leakiness at the human-animal interface in Southeast Asia and implications for the spread of antibiotic resistance

International efforts to curb antimicrobial resistance have focused on drug development and limiting unnecessary use. However, in areas where water, sanitation, and hygiene infrastructure is lacking, and where biosecurity in food-animal production is poor, pathogen-flow between humans and animals could exacerbate the emergence and spread of resistant pathogens. Here, we compared mobile resistance elements among Escherichia coli recovered from humans and meat in Cambodia, a country with substantial connectivity between humans and animals, unregulated antibiotic use, and poor environmental controls. We identified multiple resistance-encoding plasmids and a novel, blaCTX-M and qnrS1-encoding transposon that were widely dispersed in both humans and animals, a phenomenon rarely observed in high-income settings. Our findings indicate that plugging leaks at human-animal interfaces should be a critical part of addressing antimicrobial resistance in low and middle-income countries.

ecology↗

bioRxiv2020

Klebsiella MALDI TypeR: a web-based tool for Klebsiella identification based on MALDI-TOF mass spectrometry

MotivationKlebsiella species are increasingly multidrug resistant pathogens affecting human and animal health and are widely distributed in the environment. Among these, the Klebsiella pneumoniae species complex (KpSC), which includes seven phylogroups, is an important cause of community and hospital infections. In addition, the Klebsiella oxytoca species complex (KoSC) also causes hospital infections and antibiotic-associated haemorrhagic colitis. The unsuitability of widely used clinical microbiology methods to distinguish species within each of these species complexes leads to high rates of misidentifications that are masking the true clinical significance and potential epidemiological specificities of individual species. ResultsWe developed a web-based tool, Klebsiella MALDI TypeR, a platform-independent and user-friendly application that enables uploading raw data from MALDI-TOF mass spectrometer to identify Klebsiella isolates at the species complex and phylogroup levels. The tool is based on a database of previously identified biomarkers that are specific for either the species complex, individual phylogroups, or related phylogroups, and is available at https://maldityper.pasteur.fr.

bioinformatics↗

bioRxiv2019

The ZKIR Assay, a novel Real-Time PCR Method for the Detection of Klebsiella pneumoniae and Closely Related Species in Environmental Samples

Klebsiella pneumoniae (Kp) is of growing public health concern due to the emergence of strains that are multidrug-resistant, virulent, or both. Taxonomically, Kp includes seven phylogroups, with Kp1 (K. pneumoniae sensu stricto) being medically prominent. Kp can be present in environmental sources such as soils and vegetation, which could act as reservoirs of animal and human infections. However, the current lack of screening methods to detect Kp in complex matrices limits research on Kp ecology. Here we analysed 4222 genome sequences and found that existing molecular detection targets lack specificity for Kp. A novel real-time PCR method, the ZKIR assay, was developed and used to detect Kp in 96 environmental samples. Results were compared to a culture-based method using SCAI agar medium coupled to MALDI-TOF mass spectrometry identification. Whole-genome sequencing of environmental Kp was performed. The ZKIR assay was positive for the 48 tested Kp reference strains, whereas 88 non-Kp strains were negative. The limit of detection of Kp in spiked soil microcosms was 1.5 x 10-1 CFU g-1 after enrichment for 24 h in LB supplemented with ampicillin, and 1.5 x 103 to 1.5 x 104 CFU g-1 directly after soil DNA extraction. The ZKIR assay was more sensitive than the culture method. Kp was detected in 43% of environmental samples. Genomic analysis of the isolates revealed a predominance of phylogroups Kp1 (65%) and Kp3 (32%), a high genetic diversity (23 MLST sequence types), a quasi-absence of antibiotic resistance or virulence genes, and a high frequency (50%) of O-antigen type 3. This study shows that the ZKIR assay is an accurate, specific and sensitive novel method to detect the presence of Kp in complex matrices, and indicates that Kp isolates from environmental samples differ from clinical isolates. IMPORTANCEThe Klebsiella pneumoniae species complex (Kp) includes human and animal pathogens, some of which are emerging as hypervirulent and/or antibiotic resistant strains. These pathogens are diverse and classified into seven phylogroups, which may differ in their reservoirs and epidemiology. Proper management of this public health hazard requires a better understanding of Kp ecology and routes of transmission to humans. So far, detection of these microorganisms in complex matrices such as food or the environment has been difficult due to a lack of accurate and sensitive methods. Here, we describe a novel method based on real-time PCR, which enables detection of all Kp phylogroups with high sensitivity and specificity. We used this method to detect Kp isolates from environmental samples, and show based on genomic sequencing that they differ in antimicrobial resistance and virulence gene content, from human clinical Kp isolates. The ZKIR PCR assay will enable rapid screening of multiple samples for Kp presence and will thereby facilitate tracking the dispersal patterns of these pathogenic strains across environmental, food, animal and human sources.

microbiology↗

bioRxiv2019

Description of Corynebacterium rouxii sp. nov., a novel member of the diphtheriae species complex

A group of six clinical isolates previously identified as Corynebacterium diphtheriae biovar Belfanti, isolated from human cutaneous or peritoneum infections and from one dog, were characterized by genomic sequencing, biochemical analysis and mass spectrometry (MALDI-TOF MS). The six isolates were negative for the diphtheria toxin gene. Phylogenetic analyses showed that the six isolates (including FRC0190T) are clearly demarcated from C. diphtheriae, C. belfantii, C. ulcerans and C. pseudotuberculosis. The average nucleotide identity of FRC0190T with C. diphtheriae NCTC 11397T was 92.6%, and was 91.8% with C. belfantii FRC0043T. C. diphtheriae subsp. lausannense strain CHUV2995T appeared to be a later heterotypic synonym of C. belfantii (ANI, 99.3%). Phenotyping data revealed an atypical negative or heterogeneous intermediate maltose fermentation reaction for the six isolates. MALDI-TOF MS differentiated the new group from the other Corynebacterium taxa by the presence of specific spectral peaks. rpoB sequences showed identity to atypical, maltose-negative C. diphtheriae biovar Belfanti isolates previously described from two cats in the USA. We propose the name Corynebacterium rouxii sp. nov. for the novel group, with FRC0190T (= CIP 111752T = DSM 110354T) as type strain.

microbiology↗

bioRxiv2019

Description of Klebsiella spallanzanii sp. nov. and of Klebsiella pasteurii sp. nov.

Klebsiella oxytoca causes opportunistic human infections and post-antibiotic haemorrhagic diarrhoea. This Enterobacteriaceae species is genetically heterogeneous and is currently subdivided into seven phylogroups (Ko1 to Ko4, Ko6 to Ko8). Here we investigated the taxonomic status of phylogroups Ko3 and Ko4. Genomic sequence-based phylogenetic analyses demonstrate that Ko3 and Ko4 formed well-defined sequence clusters related to, but distinct from, Klebsiella michiganensis (Ko1), Klebsiella oxytoca (Ko2), K. huaxiensis (Ko8) and K. grimontii (Ko6). The average nucleotide identity of Ko3 and Ko4 were 90.7% with K. huaxiensis and 95.5% with K. grimontii, respectively. In addition, three strains of K. huaxiensis, a species so far described based on a single strain from a urinary tract infection patient in China, were isolated from cattle and human faeces. Biochemical and MALDI-ToF mass spectrometry analysis allowed differentiating Ko3, Ko4 and Ko8 from the other K. oxytoca species. Based on these results, we propose the names Klebsiella spallanzanii for the Ko3 phylogroup, with SPARK_775_C1T (CIP 111695T, DSM 109531T) as type strain, and Klebsiella pasteurii for Ko4, with SPARK_836_C1T (CIP 111696T, DSM 109530T) as type strain. Strains of K. spallanzanii were isolated from human urine, cow faeces and farm surfaces, while strains of K. pasteurii were found in faecal carriage from humans, cows and turtles.\n\nAccession numbersThe nucleotide sequences generated in this study were deposited in ENA and are available through the INSDC databases under accession numbers MN091365 (SB6411T = SPARK775C1T), MN091366 (SB6412 T = SPARK836C1T) and MN104661 to MN104677 (16S rRNA), MN076606 to MN076643 (gyrA and rpoB), and MN030558 to MN030567 (blaOXY). Complete genomic sequences were submitted to European Nucleotide Archive under the BioProject number PRJEB15325.\n\nAbbreviationsANI, average nucleotide identity; HCCA, a-cyano-4-hydroxycinnamic acid; isDDH, in silico DNA-DNA hybridization; SCAI, Simmons citrate agar with inositol; MALDI57 ToF MS: Matrix-assisted laser desorption/ionization time of flight mass spectrometry

microbiology↗

bioRxiv2019

Description of Klebsiella africanensis sp. nov., Klebsiella variicola subsp. tropicalensis subsp. nov. and Klebsiella variicola subsp. variicola subsp. nov.

The bacterial pathogen Klebsiella pneumoniae comprises several phylogenetic groups (Kp1 to Kp7), two of which (Kp5 and Kp7) have no taxonomic status. Here we show that group Kp5 is closely related to Klebsiella variicola (Kp3), with an average nucleotide identity (ANI) of 96.4%, and that group Kp7 has an ANI of 94.7% with Kp1 (K. pneumoniae sensu stricto). Biochemical characteristics and chromosomal beta-lactamase genes also distinguish groups Kp5 and Kp7 from other Klebsiella taxa. We propose the names K. africanensis for Kp7 (type strain, 200023T) and K. variicola subsp. tropicalensis for Kp5 (type strain, 1266T).

microbiology↗

bioRxiv2018

Identification of Klebsiella pneumoniae complex members using MALDI-TOF mass spectrometry

Klebsiella pneumoniae (phylogroup Kp1), one of the most problematic pathogens associated with antibiotic resistance worldwide, is phylogenetically closely related to K. quasipneumoniae [subsp. quasipneumoniae (Kp2) and subsp. similipneumoniae (Kp4)], K. variicola (Kp3) and two unnamed phylogroups (Kp5 and Kp6). Together, Kp1 to Kp6 make-up the K. pneumoniae complex. Currently, the phylogroups can be reliably identified only by gene sequencing. Misidentification using standard methods is common and the clinical significance of K. pneumoniae complex members is therefore imprecisely defined. Here, we evaluated the potential of MALDI-TOF mass spectrometry to discriminate K. pneumoniae complex members. We report for the first time the existence of mass spectrometry biomarkers associated with the phylogroups, with a sensitivity and specificity ranging between 80-100% and 97-100%, respectively. Strains within phylogroups Kp1, Kp2, Kp4 and Kp5 each shared two specific peaks not observed in other phylogroups. Kp3 strains shared a peak that was only observed otherwise in Kp5. Finally, Kp6 had a diagnostic peak shared only with Kp1. Kp3 and Kp6 could therefore be identified by exclusion criteria (lacking Kp5 and Kp1-specific peaks, respectively). Further, ranked Pearson correlation clustering of spectra grouped strains according to their phylogroup. These results call for incorporation of spectra of all K. pneumoniae complex members into reference MALDI-TOF spectra databases, in which they are currently lacking. This advance may allow for simple and precise identification of K. pneumoniae and closely related species, opening the way to a better understanding of their epidemiology, ecology and pathogenesis.

microbiology↗

bioRxiv2017

Population genomics of hypervirulent Klebsiella pneumoniae clonal group 23 reveals early emergence and rapid global dissemination

Since the mid-1980s there have been increasing reports of severe community-acquired pyogenic liver abscess, meningitis and bloodstream infections caused by hypervirulent Klebsiella pneumoniae, predominantly encompassing clonal group (CG) 23 serotype K1 strains. Common features of CG23 include a virulence plasmid associated with iron scavenging and hypermucoidy, and a chromosomal integrative and conjugative element (ICE) encoding the siderophore yersiniabactin and the genotoxin colibactin. Here we investigate the evolutionary history and genomic diversity of CG23 based on comparative analysis of 98 genomes. Contrary to previous reports with more limited samples, we show that CG23 comprises several deep branching sublineages dating back to the 1870s, many of which are associated with distinct chromosomal insertions of ICEs encoding yersiniabactin. We find that most liver abscess isolates (>80%) belong to a dominant sublineage, CG23-I, which emerged in the 1920s following acquisition of ICEKp10 (encoding colibactin in addition to yersiniabactin) and has undergone clonal expansion and global dissemination within the human population. The unique genomic feature of CG23-I is the production of colibactin, which has been reported previously as a promoter of gut colonisation and dissemination to the liver and brain in a mouse model of CG23 K. pneumoniae infection, and has been linked to colorectal cancer. We also identify an antibiotic-resistant subclade of CG23-I associated with sexually-transmitted infections in horses dating back to the 1980s. These data show that hypervirulent CG23 K. pneumoniae was circulating in humans for decades before the liver abscess epidemic was first recognised, and has the capacity to acquire and maintain AMR plasmids. These data provide a framework for future epidemiological and experimental studies of hypervirulent K. pneumoniae. To further support such studies we present an open access and completely sequenced human liver abscess isolate, SGH10, which is typical of the globally disseminated CG23-I sublineage.

genomics↗