Inaccurate Multilocus Sequence Typing of Acinetobacter baumannii.
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ABSTRACT:
SUBMITTER: Castillo-Ramirez S
PROVIDER: S-EPMC6302598 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Acinetobacter species assigned to the Acinetobacter calcoaceticus-baumannii (Acb) complex, are Gram-negative bacteria responsible for a large number of human infections. The population structure of Acb has been studied using two 7-gene MLST schemes, introduced by Bartual and coworkers (Oxford scheme) and by Diancourt and coworkers (Pasteur scheme). The schemes have three genes in common but underlie two coexisting nomenclatures of sequence types and clonal complexes, which complicates communication on A. baumannii genotypes. The aim of this study was to compare the characteristics of the two schemes to make a recommendation about their usage. Using genome sequences of 730 strains of the Acb complex, we evaluated the phylogenetic congruence of MLST schemes, the correspondence between sequence types, their discriminative power and genotyping reliability from genomic sequences. In silico ST re-assignments highlighted the presence of a second copy of the Oxford gdhB locus, present in 553/730 genomes that has led to the creation of artefactual profiles and STs. The reliability of the two MLST schemes was tested statistically comparing MLST-based phylogenies to two reference phylogenies (core-genome genes and genome-wide SNPs) using topology-based and likelihood-based tests. Additionally, each MLST gene fragment was evaluated by correlating the pairwise nucleotide distances between each pair of genomes calculated on the core-genome and on each single gene fragment. The Pasteur scheme appears to be less discriminant among closely related isolates, but less affected by homologous recombination and more appropriate for precise strain classification in clonal groups, which within this scheme are more often correctly monophyletic. Statistical tests evaluate the tree deriving from the Oxford scheme as more similar to the reference genome trees. Our results, together with previous work, indicate that the Oxford scheme has important issues: gdhB paralogy, recombination, primers sequences, position of the genes on the genome. While there is no complete agreement in all analyses, when considered as a whole the above results indicate that the Pasteur scheme is more appropriate for population biology and epidemiological studies of A. baumannii and related species and we propose that it should be the scheme of choice during the transition toward, and in parallel with, core genome MLST.
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Project description:In this study a multilocus sequence typing (MLST) scheme for Acinetobacter baumannii was developed and evaluated by using 40 clinical A. baumannii isolates recovered from outbreaks in Spanish and German hospitals during the years 1990 to 2001, as well as isolates from other European hospitals and two DSMZ reference strains of A. baumannii. For comparison, two isolates of Acinetobacter species 13 (sensu Tjernberg and Ursing), two clinical isolates, and three DSMZ strains of A. calcoaceticus (both belonging to the A. calcoaceticus-A. baumannii complex) were also investigated. Primers were designed for conserved regions of housekeeping genes, and 305- to 513-bp internal fragments of seven such genes-gltA, gyrB, gdhB, recA, cpn60, gpi, and rpoD-were sequenced for all strains. The number of alleles at individual loci ranged from 6 to 12, and a total of 20 allelic profiles or sequence types were distinguished among the investigated A. baumannii strains. The MLST data were in high concordance with the epidemiologic typing results generated by pulsed-field gel electrophoresis and amplified fragment length polymorphism fingerprinting. The MLST scheme provides a high level of resolution and an excellent tool for studying the population structure and long-term epidemiology of A. baumannii.
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Project description:We have employed whole genome sequencing to define and evaluate a core genome multilocus sequence typing (cgMLST) scheme for Acinetobacter baumannii. To define a core genome we downloaded a total of 1,573 putative A. baumannii genomes from NCBI as well as representative isolates belonging to the eight previously described international A. baumannii clonal lineages. The core genome was then employed against a total of fifty-three carbapenem-resistant A. baumannii isolates that were previously typed by PFGE and linked to hospital outbreaks in eight German cities. We defined a core genome of 2,390 genes of which an average 98.4% were called successfully from 1,339 A. baumannii genomes, while Acinetobacter nosocomialis, Acinetobacter pittii, and Acinetobacter calcoaceticus resulted in 71.2%, 33.3%, and 23.2% good targets, respectively. When tested against the previously identified outbreak strains, we found good correlation between PFGE and cgMLST clustering, with 0-8 allelic differences within a pulsotype, and 40-2,166 differences between pulsotypes. The highest number of allelic differences was between the isolates representing the international clones. This typing scheme was highly discriminatory and identified separate A. baumannii outbreaks. Moreover, because a standardised cgMLST nomenclature is used, the system will allow inter-laboratory exchange of data.
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Project description:Acinetobacter baumannii is a leading pathogen responsible for nosocomial infections. The emergence of carbapenem-resistant A. baumannii (CRAB) has left few effective antibiotics for clinicians to use. To investigate the temporal evolutionary relationships among CRAB strains, we collected 248 CRAB isolates from a Chinese burns institute over 3 years. The prevalence of the OXA-23 gene was detected by polymerase chain reaction. Multilocus sequence typing was used to type the CRAB strains and eBURST was used to analyze their evolutionary relationships. Wound surfaces (41%), sputa (24%), catheters (15%), and bloods (14%) were the four dominant isolation sources. Except for minocycline (33.5%) and sulbactam/cefoperazone (74.6%), these CRAB strains showed high resistance rates (>90%) to 16 tested antibiotics. The 248 isolates fall into 26 sequence types (STs), including nine known STs and 17 unknown STs. The majority (230/248) of these isolates belong to clonal complex 92 (CC92), including eight isolates belonging to seven unreported STs. A new CC containing 11 isolates grouped into four new STs was identified. The OXA-23 gene was detected at high prevalence among the CRAB isolates and the prevalence rate among the various STs differed. The majority of the isolates displayed a close evolutionary relationship, suggesting that serious nosocomial spreading and nosocomial infections of CRAB have occurred in the burn unit. In conclusion, the main CC for CRAB in this Chinese burn unit remained unchanged during the 3-year study period, and a new CC was identified. CC92 was the dominant complex, and more attention should be directed toward monitoring the new CC we have identified herein.
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Project description:Antimicrobial resistance issues have become a global health concern. The rapid identification of multidrug-resistant microbes, which depends on microbial genomic information, is essential for overcoming growing antimicrobial resistance challenges. However, genotyping methods, such as multilocus sequence typing (MLST), for identifying international epidemic clones of Acinetobacter baumannii are not easily performed as routine tests in ordinary clinical laboratories. In this study, we aimed to develop a novel genotyping method that can be performed in ordinary microbiology laboratories. Several open reading frames (ORFs) specific to certain bacterial genetic lineages or species, together with their unique distribution patterns on the chromosomes showing a good correlation with the results of MLST, were selected in A. baumannii and other Acinetobacter spp. by comparing their genomic data. The distribution patterns of the ORFs were visualized by agarose gel electrophoresis after multiplex PCR amplification and digitized. A. baumannii sequence types (STs) corresponding to international clones I and II were successfully discriminated from other STs and Acinetobacter species by detecting the distribution patterns of their ORFs using the multiplex PCR developed here. Since bacterial STs can be easily expressed as digitized numeric data with plus (+) expressed as 1 and minus (-) expressed as 0, the results of the method can be easily compared with those obtained by different tests or laboratories. This PCR-based ORF typing (POT) method can easily and rapidly identify international epidemic clones of A. baumannii and differentiate this microbe from other Acinetobacter spp. Since this POT method is easy enough to be performed even in ordinary clinical laboratories, it would also contribute to daily infection control measures and surveillance.
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Project description:Mycobacterium xenopi is an opportunistic mycobacterial pathogen of increasing clinical importance. Surveillance of M. xenopi is hampered by the absence of tools for genotyping and molecular epidemiology. In this study, we describe the development and evaluation of an effective multilocus sequence typing strategy for M. xenopi.
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Project description:PCR primers targeting loci in the current Burkholderia cepacia complex multilocus sequence typing scheme were redesigned to (i) more reliably amplify these loci from B. cepacia complex species, (ii) amplify these same loci from additional Burkholderia species, and (iii) enable the use of a single primer set per locus for both amplification and DNA sequencing.
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Project description:Because the lack of typing tools for Cyclospora cayetanensis has hampered outbreak investigations, we sequenced its genome and developed a genotyping tool. We observed 2 to 10 geographically segregated sequence types at each of 5 selected loci. This new tool could be useful for case linkage and infection/contamination source tracking.
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Project description:A multilocus sequence typing (MLST) scheme has been developed for Enterococcus faecium. Internal fragments from seven housekeeping genes of 123 epidemiologically unlinked isolates from humans and livestock and 16 human-derived isolates from several outbreaks in the United States, the United Kingdom, Australia, and The Netherlands were analyzed. A total of 62 sequence types were detected in vancomycin-sensitive E. faecium (VSEF) and vancomycin-resistant E. faecium (VREF) isolates. VSEF isolates were genetically more diverse than VREF isolates. Both VSEF and VREF isolates clustered in host-specific lineages that were similar to the host-specific clustering obtained by amplified fragment length polymorphism analysis. Outbreak isolates from hospitalized humans clustered in a subgroup that was defined by the presence of a unique allele from the housekeeping gene purK and the surface protein gene esp. The MLST results suggest that epidemic lineages of E. faecium emerged recently worldwide, while genetic variation in both VREF and VSEF was created by longer-term recombination. The results show that MLST of E. faecium provides an excellent tool for isolate characterization and long-term epidemiologic analysis.
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Project description:We evaluated three multilocus sequence typing (MLST) schemes for Staphylococcus epidermidis and selected the seven most discriminatory loci for the formation of a new, more powerful MLST scheme. This improved scheme gave 31 sequence types (STs) and 5 clonal complexes (CCs), whereas the other schemes delineate 16 to 24 STs and 1 to 3 CCs.
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