Biology subjects

Firth, C.

Publications and source records attributed to Firth, C..

5 recordsLinked to original sources

bioRxiv2022

Genomic neighbor typing for bacterial outbreaksurveillance

Genomic neighbor typing enables heuristic inference of bacterial lineages and phenotypes from nanopore sequencing data. However, small reference databases may not be sufficiently representative of the diversity of lineages and genotypes present in a collection of isolates. In this study, we explore the use of genomic neighbor typing for surveillance of community-associated Staphylococcus aureus outbreaks in Papua New Guinea (PNG) and Far North Queensland, Australia (FNQ). We developed Sketchy, an implementation of genomic neighbor typing that queries exhaustive whole genome reference databases using MinHash. Evaluations were conducted using nanopore read simulations and six species-wide reference sketches (4832 - 47616 genomes), as well as two S. aureus outbreak data sets sequenced at low depth using a sequential multiplex library protocol on the MinION (n = 160, with matching Illumina data). Heuristic inference of lineages and antimicrobial resistance profiles allowed us to conduct multiplex genotyping in situ at the Papua New Guinea Institute of Medical Research in Goroka, on low-throughput Flongle adapters and using multiple successive libraries on the same MinION flow cell (n = 24 - 48). Comparison to phylogenetically informed genomic neighbor typing with RASE on the dominant outbreak sequence type suggests slightly better performance at predicting lineage-scale genotypes using large sketch sizes, but inferior performance in resolving clade-specific genotypes (methicillin resistance). Sketchy can be used for large-scale bacterial outbreak surveillance and in challenging sequencing scenarios, but improvements to clade-specific genotype inference are needed for diagnostic applications. Sketchy is available open-source at: https://github.com/esteinig/sketchy

bioinformatics↗

bioRxiv2021

Taxonomic classification methods reveal a new subgenus in the paramyxovirus subfamily Orthoparamyxovirinae

As part of a broad One Health surveillance effort to detect novel viruses in wildlife and people, we report several paramyxoviruses sequenced primarily from bats during 2013 and 2014 in Brazil and Malaysia, including seven from which we recovered full-length genomes. Of these, six represent the first full-length paramyxovirus genomes sequenced from the Americas, including two sequences which are the first full-length bat morbillivirus genomes published to date. Our findings add to the vast number of viral sequences in public repositories that have been increasing considerably in recent years due to the rising accessibility of metagenomics. Taxonomic classification of these sequences in the absence of phenotypic data has been a significant challenge, particularly in the paramyxovirus subfamily Orthoparamyxovirinae, where the rate of discovery of novel sequences has been substantial. Using pairwise amino acid sequence classification (PASC), we describe a novel genus within this subfamily tentatively named Jeishaanvirus, which we propose should include as subgenera Jeilongvirus, Shaanvirus, and a novel South American subgenus Cadivirus. We also highlight inconsistencies in the classification of Tupaia virus and Mojiang virus using the same demarcation criteria and show that members of the proposed subgenus Shaanvirus are paraphyletic. Importantly, this study underscores the critical importance of sequence length in PASC analysis as well as the importance of biological characteristics such as genome organization in the taxonomic classification of viral sequences.

microbiology↗

bioRxiv2021

Phylodynamic modelling of bacterial outbreaks using nanopore sequencing

Nanopore sequencing and phylodynamic modelling have been used to reconstruct the transmission dynamics of viral epidemics, but their application to bacterial pathogens has remained challenging. Here, we implement Random Forest models for single nucleotide polymorphism (SNP) polishing to estimate divergence and effective reproduction numbers (Re) of two community-associated, methicillin-resistant Staphylococcus aureus (MRSA) outbreaks in remote Far North Queensland and Papua New Guinea (n = 159). Successive bar-coded panels of S. aureus isolates (2 x 12 per MinION) sequenced at low-coverage (> 5x - 10x) provided sufficient data to accurately infer assembly genotypes with high recall when compared with Illumina references. De novo SNP calling with Clair was followed by SNP polishing using intra- and inter-species models trained on Snippy reference calls. Models achieved sufficient resolution on ST93 outbreak sequence types (> 70 - 90% accuracy and precision) for phylodynamic modelling from lineage-wide hybrid alignments and birth-death skyline models in BEAST2. Our method reproduced phylogenetic topology, geographical source of the outbreaks, and indications of sustained transmission (Re > 1). We provide Nextflow pipelines that implement SNP polisher training, evaluation, and outbreak alignments, enabling reconstruction of within-lineage transmission dynamics for infection control of bacterial disease outbreaks using nanopore sequencing.

bioinformatics↗

bioRxiv2021

Phylodynamic signatures in the emergence of community-associated MRSA

Community-associated, methicillin-resistant Staphylococcus aureus (MRSA) lineages have emerged in many geographically distinct regions around the world during the past 30 years. Here, we apply consistent phylodynamic methods across multiple community-associated MRSA lineages to describe and contrast their patterns of emergence and dissemination. We generated whole genome sequencing data for the Australian sequence type (ST) 93-MRSA-IV from remote communities in Far North Queensland and Papua New Guinea, and the Bengal Bay ST772-MRSA-V clone from metropolitan communities in Pakistan. Increases in the effective reproduction number (Re) and sustained transmission (Re > 1) coincided with spread of progenitor methicillin-susceptible S. aureus (MSSA) in remote northern Australia, dissemination of the ST93-MRSA-IV geno-type into population centers on the Australian East Coast, and sub-sequent importation into the highlands of Papua New Guinea and Far North Queensland. Analysis of a ST772-MRSA-V cluster in Pakistan suggests that sustained transmission in the community following importation of resistant genotypes may be more common than previously thought. Applying the same phylodynamic methods to existing lineage datasets, we identified common signatures of epidemic growth in the emergence and epidemiological trajectory of community-associated S. aureus lineages from America, Asia, Australasia and Europe. Surges in Re were observed at the divergence of antibiotic resistant strains, coinciding with their establishment in regional population centers. Epidemic growth was also observed amongst drug-resistant MSSA clades in Africa and northern Australia. Our data suggest that the emergence of community-associated MRSA and MSSA lineages in the late 20th century was driven by a combination of antibiotic resistant genotypes and host epidemiology, leading to abrupt changes in lineage-wide transmission dynamics and sustained transmission in regional population centers.

evolutionary biology↗

bioRxiv2021

Rats in the city: implications for zoonotic disease risk in an urbanizing world

Urbanization is rapidly transforming much of Southeast Asia, altering the structure and function of the landscape, as well as the frequency and intensity of the interactions between people, animals, and the environment. In this study, we began to explore the impact of urbanization on zoonotic disease risk by simultaneously characterizing changes in the abundance and diversity of reservoir hosts (rodents), ectoparasite vectors (ticks), and microbial pathogens across a gradient of urbanization in Malaysian Borneo. We found that although rodent species diversity decreased with increasing urbanization, two species appeared to thrive in anthropogenic environments: the invasive urban exploiter, Rattus rattus and the native urban adapter, Sundamys muelleri. R. rattus was strongly associated with the presence of built infrastructure across the gradient and dominated the urban rodent community where it was associated with high microbial diversity and multi-host zoonoses capable of environmental transmission, including Leptospira spp., and Toxoplasma gondii. In contrast, S. muelleri was restricted to sites with a significant vegetative component where it was found at high densities in the urban location. This species was strongly associated with the presence of ticks, including the medically important genera Ambylomma, Haemaphysalis, and Ixodes. Overall, our results demonstrate that the response to urbanization varies by species at all levels: host, ectoparasite, and microbe. This may lead to increased zoonotic disease risk in a subset of environments across urban and urbanizing landscapes that can be reduced through improved pest management and public health messaging.

ecology↗