Biochemistry and Pharmacology - Research Publications

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    ESBL plasmids in Klebsiella pneumoniae: diversity, transmission and contribution to infection burden in the hospital setting
    Hawkey, J ; Wyres, KL ; Judd, LM ; Harshegyi, T ; Blakeway, L ; Wick, RR ; Jenney, AWJ ; Holt, KE (BMC, 2022-08-23)
    BACKGROUND: Resistance to third-generation cephalosporins, often mediated by extended-spectrum beta-lactamases (ESBLs), is a considerable issue in hospital-associated infections as few drugs remain for treatment. ESBL genes are often located on large plasmids that transfer horizontally between strains and species of Enterobacteriaceae and frequently confer resistance to additional drug classes. Whilst plasmid transmission is recognised to occur in the hospital setting, the frequency and impact of plasmid transmission on infection burden, compared to ESBL + strain transmission, is not well understood. METHODS: We sequenced the genomes of clinical and carriage isolates of Klebsiella pneumoniae species complex from a year-long hospital surveillance study to investigate ESBL burden and plasmid transmission in an Australian hospital. Long-term persistence of a key transmitted ESBL + plasmid was investigated via sequencing of ceftriaxone-resistant isolates during 4 years of follow-up, beginning 3 years after the initial study. RESULTS: We found 25 distinct ESBL plasmids. We identified one plasmid, which we called Plasmid A, that carried blaCTX-M-15 in an IncF backbone similar to pKPN-307. Plasmid A was transmitted at least four times into different Klebsiella species/lineages and was responsible for half of all ESBL episodes during the initial 1-year study period. Three of the Plasmid A-positive strains persisted locally 3-6 years later, and Plasmid A was detected in two additional strain backgrounds. Overall Plasmid A accounted for 21% of ESBL + infections in the follow-up period. CONCLUSIONS: Here, we systematically surveyed ESBL strain and plasmid transmission over 1 year in a single hospital network. Whilst ESBL plasmid transmission events were rare in this setting, they had a significant and sustained impact on the burden of ceftriaxone-resistant and multidrug-resistant infections. If onward transmission of Plasmid A-carrying strains could have been prevented, this may have reduced the number of opportunities for Plasmid A to transmit and create novel ESBL + strains, as well as reducing overall ESBL infection burden.
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    Genomic dissection of Klebsiella pneumoniae infections in hospital patients reveals insights into an opportunistic pathogen
    Gorrie, CL ; Mirceta, M ; Wick, RR ; Judd, LM ; Lam, MMC ; Gomi, R ; Abbott, IJ ; Thomson, NR ; Strugnell, RA ; Pratt, NF ; Garlick, JS ; Watson, KM ; Hunter, PC ; Pilcher, DV ; McGloughlin, SA ; Spelman, DW ; Wyres, KL ; Jenney, AWJ ; Holt, KE (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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    Kaptive 2.0: updated capsule and lipopolysaccharide locus typing for the Klebsiella pneumoniae species complex
    Lam, MMC ; Wick, RR ; Judd, LM ; Holt, KE ; Wyres, KL (MICROBIOLOGY SOC, 2022-03)
    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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    Linear plasmids in Klebsiella and other Enterobacteriaceae
    Hawkey, J ; Cottingham, H ; Tokolyi, A ; Wick, RR ; Judd, LM ; Cerdeira, L ; Garcia, DDO ; Wyres, KL ; Holt, KE (MICROBIOLOGY SOC, 2022-04)
    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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    Rapid Whole Genome Sequencing of Serotype K1 Hypervirulent Klebsiella pneumoniae from an Undocumented Chinese Migrant
    Macleod, CK ; Khokhar, FA ; Warne, B ; Wick, R ; Butcher, R ; Cassimon, B ; Hayden, P ; Holt, K ; Torok, ME ; Majumder, S (HINDAWI LTD, 2021-04-28)
    BACKGROUND: Hypervirulent Klebsiella pneumoniae causes severe disseminated infections, typically with hepatic and central nervous system involvement including endophthalmitis. Case Presentation. We report a fatal case of an undocumented Chinese migrant in her 60s who presented to the emergency department with abdominal pain, lethargy, and headache over the preceding two weeks. She had a new diagnosis of diabetes mellitus on admission. Computed tomography scan of the thorax, abdomen, and pelvis showed bilateral pneumonia with liver abscesses. The patient was treated with empirical broad-spectrum antibiotics before K. pneumoniae was isolated from cerebrospinal fluid and blood cultures. The isolate was further characterised as a ST23 (ST: sequence type), serotype K1 hypervirulent strain using Nanopore sequencing. Despite admission to the intensive care unit, the patient died within 48 hrs of admission. CONCLUSIONS: This case demonstrates the need for increased awareness of hypervirulent K. pneumoniae, even in countries where it occurs infrequently. Novel, rapid, sequencing technologies can support diagnosis in unusual presentations.
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    Polypolish: Short-read polishing of long-read bacterial genome assemblies
    Wick, RR ; Holt, KE ; Schneidman-Duhovny, D (PUBLIC LIBRARY SCIENCE, 2022-01)
    Long-read-only bacterial genome assemblies usually contain residual errors, most commonly homopolymer-length errors. Short-read polishing tools can use short reads to fix these errors, but most rely on short-read alignment which is unreliable in repeat regions. Errors in such regions are therefore challenging to fix and often remain after short-read polishing. Here we introduce Polypolish, a new short-read polisher which uses all-per-read alignments to repair errors in repeat sequences that other polishers cannot. Polypolish performed well in benchmarking tests using both simulated and real reads, and it almost never introduced errors during polishing. The best results were achieved by using Polypolish in combination with other short-read polishers.
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    Diversity and evolution of surface polysaccharide synthesis loci in Enterobacteriales (vol 14, pg 1713, 2020)
    Holt, KE ; Lassalle, F ; Wyres, KL ; Wick, R ; Mostowy, RJ (SPRINGERNATURE, 2022-05)
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    Recovery of small plasmid sequences via Oxford Nanopore sequencing
    Wick, RR ; Judd, LM ; Wyres, KL ; Holt, KE (MICROBIOLOGY SOC, 2021-08)
    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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    Trycycler: consensus long-read assemblies for bacterial genomes
    Wick, RR ; Judd, LM ; Cerdeira, LT ; Hawkey, J ; Meric, G ; Vezina, B ; Wyres, KL ; Holt, KE (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.
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    Genomic surveillance of antimicrobial resistant bacterial colonisation and infection in intensive care patients
    Wyres, KL ; Hawkey, J ; Mirceta, M ; Judd, LM ; Wick, RR ; Gorrie, CL ; Pratt, NF ; Garlick, JS ; Watson, KM ; Pilcher, DV ; McGloughlin, SA ; Abbott, IJ ; Macesic, N ; Spelman, DW ; Jenney, AWJ ; Holt, KE (BMC, 2021-07-14)
    BACKGROUND: Third-generation cephalosporin-resistant Gram-negatives (3GCR-GN) and vancomycin-resistant enterococci (VRE) are common causes of multi-drug resistant healthcare-associated infections, for which gut colonisation is considered a prerequisite. However, there remains a key knowledge gap about colonisation and infection dynamics in high-risk settings such as the intensive care unit (ICU), thus hampering infection prevention efforts. METHODS: We performed a three-month prospective genomic survey of infecting and gut-colonising 3GCR-GN and VRE among patients admitted to an Australian ICU. Bacteria were isolated from rectal swabs (n = 287 and n = 103 patients ≤2 and > 2 days from admission, respectively) and diagnostic clinical specimens between Dec 2013 and March 2014. Isolates were subjected to Illumina whole-genome sequencing (n = 127 3GCR-GN, n = 41 VRE). Multi-locus sequence types (STs) and antimicrobial resistance determinants were identified from de novo assemblies. Twenty-three isolates were selected for sequencing on the Oxford Nanopore MinION device to generate completed reference genomes (one for each ST isolated from ≥2 patients). Single nucleotide variants (SNVs) were identified by read mapping and variant calling against these references. RESULTS: Among 287 patients screened on admission, 17.4 and 8.4% were colonised by 3GCR-GN and VRE, respectively. Escherichia coli was the most common species (n = 36 episodes, 58.1%) and the most common cause of 3GCR-GN infection. Only two VRE infections were identified. The rate of infection among patients colonised with E. coli was low, but higher than those who were not colonised on admission (n = 2/33, 6% vs n = 4/254, 2%, respectively, p = 0.3). While few patients were colonised with 3GCR- Klebsiella pneumoniae or Pseudomonas aeruginosa on admission (n = 4), all such patients developed infections with the colonising strain. Genomic analyses revealed 10 putative nosocomial transmission clusters (≤20 SNVs for 3GCR-GN, ≤3 SNVs for VRE): four VRE, six 3GCR-GN, with epidemiologically linked clusters accounting for 21 and 6% of episodes, respectively (OR 4.3, p = 0.02). CONCLUSIONS: 3GCR-E. coli and VRE were the most common gut colonisers. E. coli was the most common cause of 3GCR-GN infection, but other 3GCR-GN species showed greater risk for infection in colonised patients. Larger studies are warranted to elucidate the relative risks of different colonisers and guide the use of screening in ICU infection control.