Biochemistry and Pharmacology - Research Publications
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ItemGenomic dissection of Klebsiella pneumoniae infections in hospital patients reveals insights into an opportunistic pathogen(NATURE PORTFOLIO, 2022-05-31)Klebsiella pneumoniae is a major cause of opportunistic healthcare-associated infections, which are increasingly complicated by the presence of extended-spectrum beta-lactamases (ESBLs) and carbapenem resistance. We conducted a year-long prospective surveillance study of K. pneumoniae clinical isolates in hospital patients. Whole-genome sequence (WGS) data reveals a diverse pathogen population, including other species within the K. pneumoniae species complex (18%). Several infections were caused by K. variicola/K. pneumoniae hybrids, one of which shows evidence of nosocomial transmission. A wide range of antimicrobial resistance (AMR) phenotypes are observed, and diverse genetic mechanisms identified (mainly plasmid-borne genes). ESBLs are correlated with presence of other acquired AMR genes (median n = 10). Bacterial genomic features associated with nosocomial onset are ESBLs (OR 2.34, p = 0.015) and rhamnose-positive capsules (OR 3.12, p < 0.001). Virulence plasmid-encoded features (aerobactin, hypermucoidy) are observed at low-prevalence (<3%), mostly in community-onset cases. WGS-confirmed nosocomial transmission is implicated in just 10% of cases, but strongly associated with ESBLs (OR 21, p < 1 × 10-11). We estimate 28% risk of onward nosocomial transmission for ESBL-positive strains vs 1.7% for ESBL-negative strains. These data indicate that K. pneumoniae infections in hospitalised patients are due largely to opportunistic infections with diverse strains, with an additional burden from nosocomially-transmitted AMR strains and community-acquired hypervirulent strains.
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ItemKaptive 2.0: updated capsule and lipopolysaccharide locus typing for the Klebsiella pneumoniae species complex(MICROBIOLOGY SOC, 2022-03-01)The outer polysaccharide capsule and lipopolysaccharide (LPS) antigens are key targets for novel control strategies targeting Klebsiella pneumoniae and related taxa from the K. pneumoniae species complex (KpSC), including vaccines, phage and monoclonal antibody therapies. Given the importance and growing interest in these highly diverse surface antigens, we had previously developed Kaptive, a tool for rapidly identifying and typing capsule (K) and outer LPS (O) loci from whole genome sequence data. Here, we report two significant updates, now freely available in Kaptive 2.0 (https://github.com/katholt/kaptive): (i) the addition of 16 novel K locus sequences to the K locus reference database following an extensive search of >17 000 KpSC genomes; and (ii) enhanced O locus typing to enable prediction of the clinically relevant O2 antigen (sub)types, for which the genetic determinants have been recently described. We applied Kaptive 2.0 to a curated dataset of >12 000 public KpSC genomes to explore for the first time, to the best of our knowledge, the distribution of predicted O (sub)types across species, sampling niches and clones, which highlighted key differences in the distributions that warrant further investigation. As the uptake of genomic surveillance approaches continues to expand globally, the application of Kaptive 2.0 will generate novel insights essential for the design of effective KpSC control strategies.
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ItemNo Preview AvailableLinear plasmids in Klebsiella and other Enterobacteriaceae(MICROBIOLOGY SOC, 2022-04-01)Linear plasmids are extrachromosomal DNA elements that have been found in a small number of bacterial species. To date, the only linear plasmids described in the family Enterobacteriaceae belong to Salmonella, first found in Salmonella enterica Typhi. Here, we describe a collection of 12 isolates of the Klebsiella pneumoniae species complex in which we identified linear plasmids. Screening of assembly graphs assembled from public read sets identified linear plasmid structures in a further 13 K. pneumoniae species complex genomes. We used these 25 linear plasmid sequences to query all bacterial genome assemblies in the National Center for Biotechnology Information database, and discovered an additional 61 linear plasmid sequences in a variety of Enterobacteriaceae species. Gene content analysis divided these plasmids into five distinct phylogroups, with very few genes shared across more than two phylogroups. The majority of linear plasmid-encoded genes are of unknown function; however, each phylogroup carried its own unique toxin-antitoxin system and genes with homology to those encoding the ParAB plasmid stability system. Passage in vitro of the 12 linear plasmid-carrying Klebsiella isolates in our collection (which include representatives of all five phylogroups) indicated that these linear plasmids can be stably maintained, and our data suggest they can transmit between K. pneumoniae strains (including members of globally disseminated multidrug-resistant clones) and also between diverse Enterobacteriaceae species. The linear plasmid sequences, and representative isolates harbouring them, are made available as a resource to facilitate future studies on the evolution and function of these novel plasmids.
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ItemA curated collection of Klebsiella metabolic models reveals variable substrate usage and gene essentiality(COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT, 2022-05-01)The Klebsiella pneumoniae species complex (KpSC) is a set of seven Klebsiella taxa that are found in a variety of niches and are an important cause of opportunistic health care-associated infections in humans. Because of increasing rates of multi-drug resistance within the KpSC, there is a growing interest in better understanding the biology and metabolism of these organisms to inform novel control strategies. We collated 37 sequenced KpSC isolates isolated from a variety of niches, representing all seven taxa. We generated strain-specific genome-scale metabolic models (GEMs) for all 37 isolates and simulated growth phenotypes on 511 distinct carbon, nitrogen, sulfur, and phosphorus substrates. Models were curated and their accuracy was assessed using matched phenotypic growth data for 94 substrates (median accuracy of 96%). We explored species-specific growth capabilities and examined the impact of all possible single gene deletions using growth simulations in 145 core carbon substrates. These analyses revealed multiple strain-specific differences, within and between species, and highlight the importance of selecting a diverse range of strains when exploring KpSC metabolism. This diverse set of highly accurate GEMs could be used to inform novel drug design, enhance genomic analyses, and identify novel virulence and resistance determinants. We envisage that these 37 curated strain-specific GEMs, covering all seven taxa of the KpSC, provide a valuable resource to the Klebsiella research community.
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ItemWhole genome sequence analysis of Salmonella Typhi in Papua New Guinea reveals an established population of genotype 2.1.7 sensitive to antimicrobials(PUBLIC LIBRARY SCIENCE, 2022-03-01)BACKGROUND: Typhoid fever, a systemic infection caused by Salmonella enterica serovar Typhi, remains a considerable public health threat in impoverished regions within many low- and middle-income settings. However, we still lack a detailed understanding of the emergence, population structure, molecular mechanisms of antimicrobial resistance (AMR), and transmission dynamics of S. Typhi across many settings, particularly throughout the Asia-Pacific islands. Here we present a comprehensive whole genome sequence (WGS) based overview of S. Typhi populations circulating in Papua New Guinea (PNG) over 30 years. PRINCIPLE FINDINGS: Bioinformatic analysis of 86 S. Typhi isolates collected between 1980-2010 demonstrated that the population structure of PNG is dominated by a single genotype (2.1.7) that appears to have emerged in the Indonesian archipelago in the mid-twentieth century with minimal evidence of inter-country transmission. Genotypic and phenotypic data demonstrated that the PNG S. Typhi population appears to be susceptible to former first line drugs for treating typhoid fever (chloramphenicol, ampicillin and co-trimoxazole), as well as fluoroquinolones, third generation cephalosporins, and macrolides. PNG genotype 2.1.7 was genetically conserved, with very few deletions, and no evidence of plasmid or prophage acquisition. Genetic variation among this population was attributed to either single point mutations, or homologous recombination adjacent to repetitive ribosomal RNA operons. SIGNIFICANCE: Antimicrobials remain an effective option for the treatment of typhoid fever in PNG, along with other intervention strategies including improvements to water, sanitation and hygiene (WaSH) related infrastructure and potentially the introduction of Vi-conjugate vaccines. However, continued genomic surveillance is warranted to monitor for the emergence of AMR within local populations, or the introduction of AMR associated genotypes of S. Typhi in this setting.
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ItemSpecies interactions constrain adaptation and preserve ecological stability in an experimental microbial community(SPRINGERNATURE, 2022-01-22)Species loss within a microbial community can increase resource availability and spur adaptive evolution. Environmental shifts that cause species loss or fluctuations in community composition are expected to become more common, so it is important to understand the evolutionary forces that shape the stability and function of the emergent community. Here we study experimental cultures of a simple, ecologically stable community of Saccharomyces cerevisiae and Lactobacillus plantarum, in order to understand how the presence or absence of a species impacts coexistence over evolutionary timescales. We found that evolution in coculture led to drastically altered evolutionary outcomes for L. plantarum, but not S. cerevisiae. Both monoculture- and co-culture-evolved L. plantarum evolved dozens of mutations over 925 generations of evolution, but only L. plantarum that had evolved in isolation from S. cerevisiae lost the capacity to coexist with S. cerevisiae. We find that the evolutionary loss of ecological stability corresponds with fitness differences between monoculture-evolved L. plantarum and S. cerevisiae and genetic changes that repeatedly evolve across the replicate populations of L. plantarum. This work shows how coevolution within a community can prevent destabilising evolution in individual species, thereby preserving ecological diversity and stability, despite rapid adaptation.
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ItemNo Preview AvailablewMel Wolbachia genome remains stable after 7 years in Australian Aedes aegypti field populations(MICROBIOLOGY SOC, 2021-09-01)Infection of wMel Wolbachia in Aedes aegypti imparts two signature features that enable its application for biocontrol of dengue. First, the susceptibility of mosquitoes to viruses such as dengue and Zika is reduced. Second, a reproductive manipulation is caused that enables wMel introgression into wild-type mosquito populations. The long-term success of this method relies, in part, on evolution of the wMel genome not compromising the critical features that make it an attractive biocontrol tool. This study compared the wMel Wolbachia genome at the time of initial releases and 1-7 years post-release in Cairns, Australia. Our results show the wMel genome remains highly conserved up to 7 years post-release in gene sequence, content, synteny and structure. This work suggests the wMel genome is stable in its new mosquito host and, therefore, provides reassurance on the potential for wMel to deliver long-term public-health impacts.
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ItemNo Preview AvailableGenomic Diversity and Antimicrobial Resistance of Haemophilus Colonizing the Airways of Young Children with Cystic Fibrosis(AMER SOC MICROBIOLOGY, 2021-07-01)Respiratory infection during childhood is a key risk factor in early cystic fibrosis (CF) lung disease progression. Haemophilus influenzae and Haemophilus parainfluenzae are routinely isolated from the lungs of children with CF; however, little is known about the frequency and characteristics of Haemophilus colonization in this context. Here, we describe the detection, antimicrobial resistance (AMR), and genome sequencing of H. influenzae and H. parainfluenzae isolated from airway samples of 147 participants aged ≤12 years enrolled in the Australian Respiratory Early Surveillance Team for Cystic Fibrosis (AREST CF) program, Melbourne, Australia. The frequency of colonization per visit was 4.6% for H. influenzae and 32.1% for H. parainfluenzae, 80.3% of participants had H. influenzae and/or H. parainfluenzae detected on at least one visit, and using genomic data, we estimate 15.6% of participants had persistent colonization with the same strain for at least two consecutive visits. Isolates were genetically diverse and AMR was common, with 52% of H. influenzae and 82% of H. parainfluenzae displaying resistance to at least one drug. The genetic basis for AMR could be identified in most cases; putative novel determinants include a new plasmid encoding blaTEM-1 (ampicillin resistance), a new inhibitor-resistant blaTEM allele (augmentin resistance), and previously unreported mutations in chromosomally carried genes (pbp3, ampicillin resistance; folA/folP, cotrimoxazole resistance; rpoB, rifampicin resistance). Acquired AMR genes were more common in H. parainfluenzae than H. influenzae (51% versus 21%, P = 0.0107) and were mostly associated with the ICEHin mobile element carrying blaTEM-1, resulting in more ampicillin resistance in H. parainfluenzae (73% versus 30%, P = 0.0004). Genomic data identified six potential instances of Haemophilus transmission between participants, of which three involved participants who shared clinic visit days. IMPORTANCE Cystic fibrosis (CF) lung disease begins during infancy, and acute respiratory infections increase the risk of early disease development and progression. Microbes involved in advanced stages of CF are well characterized, but less is known about early respiratory colonizers. We report the population dynamics and genomic determinants of AMR in two early colonizer species, namely, Haemophilus influenzae and Haemophilus parainfluenzae, collected from a pediatric CF cohort. This investigation also reveals that H. parainfluenzae has a high frequency of AMR carried on mobile elements that may act as a potential reservoir for the emergence and spread of AMR to H. influenzae, which has greater clinical significance as a respiratory pathogen in children. This study provides insight into the evolution of AMR and the colonization of H. influenzae and H. parainfluenzae in a pediatric CF cohort, which will help inform future treatment.
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ItemRecovery of small plasmid sequences via Oxford Nanopore sequencing(MICROBIOLOGY SOC, 2021-08-01)Oxford Nanopore Technologies (ONT) sequencing platforms currently offer two approaches to whole-genome native-DNA library preparation: ligation and rapid. In this study, we compared these two approaches for bacterial whole-genome sequencing, with a specific aim of assessing their ability to recover small plasmid sequences. To do so, we sequenced DNA from seven plasmid-rich bacterial isolates in three different ways: ONT ligation, ONT rapid and Illumina. Using the Illumina read depths to approximate true plasmid abundance, we found that small plasmids (<20 kbp) were underrepresented in ONT ligation read sets (by a mean factor of ~4) but were not underrepresented in ONT rapid read sets. This effect correlated with plasmid size, with the smallest plasmids being the most underrepresented in ONT ligation read sets. We also found lower rates of chimaeric reads in the rapid read sets relative to ligation read sets. These results show that when small plasmid recovery is important, ONT rapid library preparations are preferable to ligation-based protocols.
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ItemTrycycler: consensus long-read assemblies for bacterial genomes(BMC, 2021-09-14)While long-read sequencing allows for the complete assembly of bacterial genomes, long-read assemblies contain a variety of errors. Here, we present Trycycler, a tool which produces a consensus assembly from multiple input assemblies of the same genome. Benchmarking showed that Trycycler assemblies contained fewer errors than assemblies constructed with a single tool. Post-assembly polishing further reduced errors and Trycycler+polishing assemblies were the most accurate genomes in our study. As Trycycler requires manual intervention, its output is not deterministic. However, we demonstrated that multiple users converge on similar assemblies that are consistently more accurate than those produced by automated assembly tools.