Biology subjects

Pascoe, B.

Publications and source records attributed to Pascoe, B..

At least 19 recordsLinked to original sources

bioRxiv2026

Insertion sequence elements associated with Staphylococcus epidermidis evolution in persistent orthopaedic device-related infections

BackgroundStaphylococcus epidermidis is a major cause of orthopaedic device-related infections (ODRIs), which are often challenging to treat due to their extensive antimicrobial resistance (AMR) and biofilm formation. It has been hypothesised that S. epidermidis may rapidly adapt to the medical device niche, enhancing persistence, but direct evidence of within-host pathoadaptive evolution remains limited. ResultsTo investigate within-host evolution during chronic infection by S. epidermidis, we analysed isolates from patients with confirmed ODRIs and used a rat infection model to examine the evolution of strains from two distinct epidemic lineages (ST2 and ST23). Our analysis revealed that the replicative transposition of insertion sequence (IS) elements within the accessory genome was the predominant mechanism of genetic diversification. This was largely driven by the IS256 family, which accounted for approximately 25% of all mutational events. However, other than SCCmec deletions resulting in the loss of mecA, no mutations, including those which exhibited parallel evolution, were predicted or observed to influence AMR or biofilm formation. These findings suggest that the strains investigated in this study, which already exhibited high-level multidrug resistance and biofilm-forming ability, were likely pre-adapted epidemic S. epidermidis clones well suited to establishing persistent ODRIs. ConclusionsOur findings highlight the prominent role of IS elements in driving genetic diversification in S. epidermidis, underscoring the need for closer examination of their contribution to pathoadaptation during persistent infection.

genomics↗

bioRxiv2026

Phenotypic Resistance of Ciprofloxacin and Azithromycin Resistant Campylobacter Isolates to an Extended Panel of Antibiotics.

In this study we explored phenotypic resistance using traditional Kirby-Bauer methods in human and animal derived Campylobacter isolates that were concurrently resistant to both azithromycin and ciprofloxacin to an expanded panel of antimicrobials, including clindamycin, fosfomycin, ampicillin sulbactam and tigecycline. Out of 236 Campylobacter isolates, over 85% of C. jejuni and C. coli were resistant to clindamycin, over 60% were resistant to ampicillin sulbactam and over 30% to fosfomycin. Less than 2% of isolates were resistant to tigecycline and there was no observed resistance to Imipenem.

microbiology↗

bioRxiv2026

A stable, hierarchical LIN code system for Campylobacter jejuni and Campylobacter coli: A unified genomic nomenclature for lineage-level typing and global surveillance.

Campylobacter remains the leading cause of bacterial gastroenteritis worldwide, with C. jejuni accounting for around 90% of infection and C. coli accounting for most of the rest. Seven-locus multilocus sequence typing (MLST) has improved our understanding of host association and population structure, whilst core genome MLST (cgMLST), enables investigation of transmission events at high-resolution. However, the lack of a stable and standardised nomenclature for clustering of cgMLST data has limited reproducibility and long-term comparability between studies. Here we introduce a joint, hierarchical Life Identification Number (LIN) code system that provides reproducible, multi-level genomic identifiers for C. jejuni and C. coli lineages. Using an updated cgMLST v2 scheme (1,142 loci) and globally representative datasets of high-quality genomes selected from over 53,000 assemblies in the Campylobacter PubMLST database (https://pubmlst.org/organisms/campylobacter-jejunicoli), we firstly defined LIN codes on a dataset of 5,664 genomes. Pairwise allelic distances were computed using MSTclust, and 18 nested thresholds were defined through silhouette, adjusted Wallace and adjusted Rand Index (ARI) statistics to capture the population structure from species to outbreak level resolution. The LIN thresholds were then validated using a second dataset of 1,781 genomes from PubMLST and applied to a large water-associated outbreak dataset from New Zealand in 2016, containing clinical and ecological genomes. Further application of LIN codes was demonstrated by analyses of the C. jejuni ST-21 clonal complex and ST-6175 isolates, as well as the broader population structure of C. coli, using data from PubMLST. Across all datasets, LIN clusters were stable, largely monophyletic, and back-compatible with existing nomenclature, accurately distinguishing host-adapted and outbreak-associated lineages. By embedding cgMLST data within a stable and scalable nomenclature, the Campylobacter LIN system delivers consistent, automated genome-to-lineage assignment. This unified framework bridges population genetics and applied surveillance, enabling robust, real-time comparison of Campylobacter isolates across sources, studies, and time. Impact statementHuman cases of Campylobacter worldwide continue unabated. Tracing the source of Campylobacter infection is particularly challenging given the sporadic or multi-source nature of outbreaks, with potential transmission from foodborne, animal or environmental sources. Seven-locus MLST has greatly improved our broad understanding of Campylobacter population structure. However, whilst high-resolution cgMLST alleles and STs themselves do not change, longitudinal cluster analyses of cgMLST data have lacked a stable nomenclature, rendering them unsuitable for robust and comparable surveillance over time. Life Identification Number (LIN) codes provide a solution to this problem, establishing an automated and scalable nomenclature derived directly from cgMLST profiles, that is stable over time. We have implemented a joint C. jejuni and C. coli LIN code scheme in PubMLST, with scripts for real-time lineage assignment. LIN codes are back-compatible with existing MLST nomenclature, and we demonstrate their added practical value for exploring population structure and high-resolution outbreak investigation. LIN codes support surveillance of Campylobacter in a One Health context, by enabling consistent typing at multiple levels across different sources, laboratories and time. Data summary1. The isolate collections used to develop the LIN codes are publicly available and searchable as individual projects on the PubMLST database (https://pubmlst.org). O_LILIN code development (Dataset 1) (n=5,664 isolates, up to 200 isolates per clonal complex) C_LIO_LILIN code validation (Dataset 2) (n=1,781 isolates), up to 50 isolates per clonal complex C_LIO_LIOutbreak investigation (Dataset 3): New Zealand 2016 Havelock North waterborne outbreak, Gilpin et al (n=161 isolates) [1] C_LIO_LIPopulation structure exploration (clonal complex) (Dataset 4): ST-21 complex (n=1800 isolates, up to 100 isolates randomly selected from each country) C_LIO_LIPopulation structure exploration (sequence type) (Dataset 5): ST-6175 (n=321 isolates, genomes with good cgMLST v2 annotation) C_LI 2. The software for LIN code development is publicly available as follows: O_LIMSTclust for pairwise distance matrices https://gitlab.pasteur.fr/GIPhy/MSTclust [2] C_LIO_LIPython script to define LIN codes in a local dataset; (https://gitlab.pasteur.fr/BEBP/LINcoding) C_LIO_LIBIGSdb Perl script to define LIN codes from cgMLST profiles on the PubMLST database; (https://github.com/kjolley/BIGSdb/blob/develop/scripts/maintenance/lincodes.pl) C_LI

microbiology↗

bioRxiv2025

Growth rates and Metabolic Traits Differentiate Campylobacter jejuni Strains by Diarrheal Manifestation

IntroductionCampylobacter jejuni is the leading cause of bacterial gastroenteritis worldwide. Infections with C. jejuni can result in two different diarrheal manifestations in humans: watery diarrhea or bloody/inflammatory diarrhea. Hypothesis/Gap StatementCurrently, little is known about C. jejuni and/or host factors associated with elicitation of these two distinct diarrheal manifestations. We hypothesize that these factors may include growth and metabolic trait differences between C. jejuni strains associated with watery diarrhea and bloody/inflammatory diarrhea. AimUsing C. jejuni strains with a defined diarrheal manifestation in the neonatal piglet model, we aimed to assess differences in temperature dependent growth rates, motility, biofilm production, and carbon utilization between diarrheal manifestation groups. MethodologyStrains were initially assessed for 192 different carbon sources using phenotypic microarrays followed by specific carbon utilization, growth, motility, and biofilm assays at 37{degrees}C and/or 42{degrees}C. ResultsWe found that at 37{degrees}C, watery diarrhea associated C. jejuni strains grew significantly faster compared to bloody/inflammatory diarrhea associated C. jejuni strains. However, there was no significant growth difference at 42{degrees}C between the groups, due to bloody/inflammatory diarrhea associated strains growing faster at 42{degrees}C compared to 37{degrees}C. Additionally at 37{degrees}C, we found that L-fucose utilization was significantly higher among watery diarrhea associated strains, while L-glutamine utilization was significantly higher among bloody/inflammatory diarrhea associated strains. ConclusionThe results indicate there are distinct metabolic adaptations between watery and/or bloody/inflammatory diarrhea associated C. jejuni strains particularly at 37{degrees}C, which may be one of the factors associated with differing diarrheal manifestations.

microbiology↗

bioRxiv2025

STRAIN-SPECIFIC VIRULENCE SIGNATURES OF CAMPYLOBACTER JEJUNI ASSOCIATED WITH WATERY VERSUS BLOODY DIARRHEA IN NEONATAL PIGLET MODEL

Campylobacter jejuni is the leading cause of bacterial gastroenteritis globally, presenting with either watery or bloody/inflammatory diarrhea. Despite this clinical variability, the underlying mechanisms driving these distinct diarrheal manifestations remain unclear. The neonatal piglet model provides a unique opportunity to investigate these differences using strains with defined disease manifestations. We evaluated ten C. jejuni strains previously shown to cause consistent diarrheal manifestations in neonatal piglets: five strains associated with watery diarrhea and five associated with bloody/inflammatory diarrhea. The study found significant strain to strain variation among most assays, but overall strains associated with bloody/inflammatory diarrhea exhibited significantly higher levels of epithelial cell invasion, intracellular survival, macrophage survivability, and disruption of intestinal barrier integrity compared to watery diarrhea strains. Notably, both groups had similar levels of adherence, produced similar levels of cytolethal distending toxin (CDT) and elicited comparable IL-8 responses. While both groups facilitated translocation of commensal E. coli, only bloody/inflammatory strains caused increased paracellular permeability, as shown by TEER and FITC-dextran assays. This study reveals that there is significant variation in the virulence phenotype of C. jejuni strains and identifies several characteristics consistently associated with a specific diarrheal manifestation group. These findings provide new insights into the strain-specific pathogenic mechanisms of C. jejuni, with implications for understanding host-pathogen interactions and informing targeted diagnostic and therapeutic strategies. Author SummaryCampylobacter jejuni is one of the most common bacterial causes of diarrhea worldwide, affecting millions each year. Infected individuals may experience either watery or bloody/inflammatory diarrhea, but the reasons why different strains cause different types of illness have remained a mystery. In this study, we used a neonatal piglet model, which accurately mimics human diarrheal disease, to investigate why certain C. jejuni strains cause more severe symptoms than others. We compared strains known to cause either watery or bloody diarrhea and found key differences in their ability to invade intestinal cells, survive inside immune cells, and damage the intestinal barrier. While both groups of strains could trigger inflammation and translocate E. coli through the intestinal lining, only the strains linked to bloody diarrhea caused significant barrier disruption and had increased intracellular survival. These findings reveal that different C. jejuni strains follow distinct paths during infection, which helps explain why they produce different symptoms. Unraveling these differences improves our overall understanding of Campylobacter pathogenesis that could lead to improved diagnostics and/or treatments to reduce the burden of campylobacteriosis around the world.

microbiology↗

bioRxiv2025

American black bear (Ursus americanus) as a potential host for Campylobacter jejuni

The Gram-negative bacterium Campylobacter jejuni is part of the commensal gut microbiota of numerous animal species and a leading cause of bacterial foodborne illness in humans. Most complete genomes of C. jejuni are from strains isolated from human clinical, poultry, and ruminant samples. Here, we characterized and compared the genomes of C. jejuni that were isolated from American black bears in three states in the southeastern United States. Despite the limited sample size (n=9), the isolates displayed substantial genotypic variability, including eight distinct sequence types (STs) and variable gene content encoding surface glycan structures such as capsular polysaccharides (CPS) and lipooligosaccharides (LOS). Phylogenetic analysis identified several C. jejuni host generalist strains among the isolates from bears that clustered with isolates from domestic poultry, cattle, and environmental sources. Three isolates (SKBC94, SKBC3, SKBC5) clustered with wildlife-associated strains, exhibiting mutations or deletions in loci associated with cytolethal distending toxin production and oxidative stress resistance, potentially influencing host-specific colonization. Additionally, strains SKBC3 and SKBC5 harbored distinct Entner-Doudoroff (E-D) loci, suggesting a potential evolutionary fitness advantage. This study provides the first evidence of C. jejuni colonization in American black bears, highlighting their potential role as reservoirs for diverse C. jejuni lineages from both anthropogenic and environmental sources. Further research is needed to determine the prevalence and host specificity of C. jejuni strains in black bears and their potential implications for public and wildlife health.

microbiology↗

bioRxiv2023

Genomic tailoring of autogenous poultry vaccines to reduce Campylobacter from farm to fork

Campylobacter is a leading cause of food-borne gastroenteritis worldwide, linked to the consumption of contaminated poultry meat. Targeting this pathogen at source, vaccines for poultry can provide short term caecal reductions in Campylobacter numbers in the chicken intestine. However, this approach is unlikely to reduce Campylobacter in the food chain or human incidence. This is likely as vaccines typically target only a subset of the high strain diversity circulating among chicken flocks and rapid evolution diminishes vaccine efficacy over time. To address this, we used a genomic approach to develop a whole-cell autogenous vaccine targeting isolates harbouring genes linked to survival outside of the host. We hyper-immunised a whole major UK breeder farm to passively target offspring colonisation using maternally-derived antibody. Monitoring progeny, broiler flocks revealed a near-complete shift in the post-vaccination Campylobacter population with a [~]50% reduction in isolates harbouring extra-intestinal survival genes and a significant reduction of Campylobacter cells surviving on the surface of meat. Based on these findings, we developed a logistic regression model that predicted that vaccine efficacy could be extended to target 46% of a population of clinically relevant strains. Immuno-manipulation of poultry microbiomes towards less harmful commensal isolates by competitive exclusion, has major potential for reducing pathogens in the food production chain.

microbiology↗

bioRxiv2023

Urbanization spreads antimicrobial resistant enteric pathogens in wild bird microbiomes

Human behaviour is dramatically changing global ecology. Nowhere is this more apparent than in urbanization, where novel high human density habitats are disrupting long established ecotones. Resultant changes to the transitional areas between organisms, especially enhanced contact between humans and wild animals, provides new opportunities for the spread of zoonotic pathogens, posing a serious threat to global public health. Here, by studying the multi-host enteric pathogen Campylobacter jejuni isolated from the gut of 30 bird species in 8 countries, we investigated how proximity to urbanization influenced the spread of antimicrobial resistant (AMR) strains. Generalized linear models compared multiple behavioural and ecological traits and confirmed a positive correlation between proximity to urbanization and the number of C. jejuni genotypes and AMR genes in wild bird hosts. Wild birds from highly urban areas harboured up to four times more C. jejuni genotypes and six times more AMR genes. This is consistent with increased frequency of transition events. Quantifying zoonotic transmission and gene pool spread is essential for quantitative one health surveillance and control measures against future zoonosis emergences.

genomics↗

bioRxiv2023

Investigation of swine caecal microbiomes in the northern region of Thailand

IntroductionThe northern region of Thailand serves as a crucial area for swine production, contributing to the global food supply. Previous studies have highlighted the presence of foodborne pathogens originating from swine farms in this region, posing a threat to both human and animal health. Gap statementMultiple swine pathogens have been studied at a species level, but the distribution and co-occurrence of pathogens in agricultural swine has not been well established. AimOur study employed the intestinal scraping technique to directly examine the microorganisms interacting with the swine host. MethodologyWe used shotgun metagenomic sequencing to analyse the caecal microbiomes of swine from five commercial farms in northern Thailand. ResultsSwine caecal microbiomes contained commensal bacteria such as Bifidobacterium, Lactobacillus, and Faecalibacterium, which are associated with healthy physiology and feed utilisation. We also identified multiple pathogenic and opportunistic bacteria present in all samples, including Escherichia coli, Clostridium botulinum, Staphylococcus aureus, and the Corynebacterium genus. From a One Health perspective, these species are important foodborne and opportunistic pathogens in both humans and agricultural animals. Antimicrobial resistance genes were also detected in all samples, specifically conferring resistance to tetracycline and aminoglycosides which have historically been used extensively in swine farming. ConclusionThe findings further support the need for improved sanitation standards in swine farms, and additional monitoring of agricultural animals and farm workers to reduce contamination and improved produce safety for human consumption.

microbiology↗

bioRxiv2023

Contrasting genes conferring short and long-term biofilm adaptation in Listeria

Listeria monocytogenes is an opportunistic food-borne bacterium that is capable of infecting humans with high rates of hospitalisation and mortality. Natural populations are genotypically and phenotypically variable, with some lineages being responsible for most human infections. The success of L. monocytogenes is linked to its capacity to persist on food and in the environment. Biofilms are an important feature that allow these bacteria to persist and infect humans, therefore, understanding the genetic basis of biofilm formation is key to understanding transmission. We sought to investigate the biofilm forming ability of L. monocytogenes by identifying genetic variation that underlies biofilm formation in natural populations using genome-wide association studies. Changes in gene expression of specific strains during biofilm formation were then investigated using RNAseq. Genetic variation associated with enhanced biofilm formation was identified in 273 genes by GWAS and differential expression in 220 genes by RNAseq. Statistical analyses show that number of overlapping genes flagged by either type of experiment is less than expected by random sampling. This is consistent with an evolutionary scenario where rapid adaptation is driven by variation in gene expression of pioneer genes, and this is followed by slower adaptation driven by nucleotide changes within the core genome. Impact statementListeria monocytogenes is a problematic food-borne bacterium that can cause severe illness and even death in humans. Some strains are known to be more common in disease and biofilms are crucial for survival in the environment and transmission to humans. To unravel the genetic basis of biofilm formation, we undertook a study employing genome-wide association studies (GWAS) and gene transcription profiling. We identified 273 genes associated with robust biofilm formation through GWAS and discovered differential expression in 220 genes through RNAseq. Statistical analysis revealed fewer overlapping genes than expected by chance, supporting an evolutionary scenario where initial adaptation relies on gene expression variation, followed by slower adaptation through genetic changes within the core genome. Data summaryShort read genome data are available from the NCBI (National Center for Biotechnology Information) SRA (Sequence Read Archive), associated with BioProject PRJNA971143 (https://www.ncbi.nlm.nih.gov/bioproject/PRJNA971143). Assembled genomes and supplementary material are available from FigShare: doi: 10.6084/m9.figshare.23148029. RNA sequence data and differential gene expression profiles have been deposited in the NCBI Gene Expression Omnibus.

microbiology↗

bioRxiv2023

Colistin resistance and resistance determinants are mobile among Salmonella enterica isolates from diseased and healthy pigs in Thailand

Salmonella is an important enteric pathogen that poses a threat to human and livestock animal health, with emerging multidrug resistance (MDR) a major public health issue globally. We investigated the prevalence of Salmonella in healthy and diseased pigs from Thai pig farms and determined their phenotypic and genotypic antimicrobial resistance profiles. A total of 150 fecal samples were collected from pigs housed in pens from four separate pig farms in southern Thailand and tested for the presence of Salmonella. Confirmed Salmonella isolates were tested for their susceptibility to 11 antimicrobials, and PCR used to detect known antimicrobial resistance genes (ARGs). Salmonella isolates were cultured from 69% (103/150) of all fecal samples, with higher prevalence in disease pigs (12/15; 80%), compared with healthy pigs (91/135; 67%). Serotype Rissen was the most frequently identified serotype among the Salmonella isolates. Resistance to ampicillin (AMP) (97%), sulfonamide-trimethoprim (SXT) (97%), and tetracycline (TET) (94%) were the most common phenotypes observed. The most common ARGs identified were blaTEM gene (99.%), tetA (87%), sul1 (77%), and dfrA1 (74%), and more than 95% of the Salmonella isolates tested were MDR - based on resistance to three or more antimicrobial classes. The most common antimicrobial resistance pattern exhibited was AMP-TET-SXT (76%), and resistance to colistin (via the mcr-1 gene) was observed in both healthy and diseased pigs. The clonal groups of PFGE analysis in serotype Typhimurium revealed the genetic relationship among Salmonella isolated from healthy and diseased pigs from different pig farms.

microbiology↗

bioRxiv2022

Assessing the pathogenic potential of less common Salmonella enterica serotypes circulating in the Thai pork production chain

Salmonella is a frequent zoonotic foodborne pathogen, with swine and pork meats the most common source of human infection. In Chiang Mai and Lamphun Province in northern Thailand, there has been a high prevalence of salmonellosis for over a decade. Infection is usually with several dominant S. enterica serotypes, including serotypes Rissen and Monophasic Typhimurium. However, several less common serotypes also contribute to disease. Whole genome sequencing of 43 of these less common S. enterica serotypes isolated from the pork production chain through 2011-2014 were used to evaluate their genetic diversity and virulence potential. Salmonella contamination at local retail markets represented cross-contamination from multiple sources, including decontaminated foodstuff. Previous studies have highlighted the importance of host cell adhesion, invasion and intracellular survival for the development of clinical salmonellosis. We screened our dataset for known virulence genes and antimicrobial resistance genes, identifying at least 10 antimicrobial resistance genes in all isolates. These results indicate that these less common S. enterica serotypes also pose a significant public health risk. Our findings support the need for appropriate surveillance of food products going to market to reduce public exposure to highly pathogenic, multi-drug resistant Salmonella. Surveillance throughout the pork production chain would motivate stakeholders to reinforce sanitation standards and help reduce the risk of salmonellosis in humans.

microbiology↗

bioRxiv2021

Local accessory gene sharing drives lineage-specific acquisition of antimicrobial resistance in Egyptian Campylobacter spp.

Campylobacter is the most common cause of bacterial gastroenteritis worldwide and diarrheal disease is a major cause of child morbidity, growth faltering and mortality in low- and middle-income countries (LMICs). Despite evidence of high incidence and differences in disease epidemiology, there is limited genomic data from studies in developing countries. In this study, we characterised the genetic diversity and accessory genome content of a collection of Campylobacter isolates from Cairo, Egypt. In total, 112 Campylobacter isolates were collected from broiler carcasses (n=31), milk and dairy products (n=24) and patients (n=57) suffering from gastroenteritis. Among the most common sequence types (STs) we identified were the globally disseminated, host generalist ST-21 clonal complex (CC21) and the poultry specialist CC206, CC464 and CC48. Notably, CC45 and the cattle-specialist CC42 were under-represented with a total absence of CC61. Comparative genomics were used to quantify core and accessory genome sharing among isolates from the same country compared to sharing between countries. Lineage-specific accessory genome sharing was significantly higher among isolates from the same country, particularly CC21 which demonstrated greater local geographical clustering. In contrast, no geographic clustering was noted in either the core or accessory genomes of the CC828, suggesting a highly admixed population. A greater proportion of C. coli isolates were multidrug resistant (MDR) compared to C. jejuni. This is a significant public health concern as MDR food chain pathogens are difficult to treat and often pose increased mortality risk demanding enhanced prevention strategies in the Egyptian market to combat such a threat. Impact statementCampylobacter is the leading bacterial cause of gastroenteritis worldwide and despite high incidence in low- and middle-income countries, where infection can be fatal, culture-based isolation is rare and the genotypes responsible for disease are seldom identified. Here, we sequenced the genomes of a collection of isolates from clinical cases and potential infection reservoirs from Cairo in Egypt and characterised their genetic diversity. Among the most common genotypes we identified were globally disseminated lineages implicated in human disease worldwide, including the host generalist ST-21 clonal complex (CC21) and the poultry specialist genotypes CC206, CC464 and CC48. Notably however, some other globally common genotypes were under-represented or entirely absent from our collection, including those from cattle-specialist lineages, CC42 and CC61. By focussing on specific lineages, we demonstrate that there is increased accessory genome sharing in specific clonal complexes. This increased local sharing of genes may have contributed to a greater proportion of C. coli isolates possessing antimicrobial resistance determinants that suggest they could be multidrug resistant (MDR). This is a significant public health concern as MDR food chain pathogens are difficult to treat and often pose increased mortality risk demanding enhanced prevention strategies. Data summaryShort read data are available on the NCBI Sequence Read Archive, associated with BioProject PRJNA576513 (https://www.ncbi.nlm.nih.gov/bioproject/PRJNA576513). Assembled genomes, supplementary material and additional analysis files are available from FigShare: https://doi.org/10.6084/m9.figshare.9956597. Phylogenetic trees can be visualised and manipulated on Microreact for C. jejuni (https://next.microreact.org/project/Cjejuni_Egypt) and C. coli (https://next.microreact.org/project/Ccoli_Egypt) separately, or combined Cairo and Oxford data with additional PopPunk network clustering (https://microreact.org/project/Campy-Egypt).

microbiology↗

bioRxiv2021

Host ecology regulates interspecies recombination in bacteria of the genus Campylobacter

Horizontal gene transfer (HGT) can allow traits that have evolved in one bacterial species to transfer to another. This has potential to rapidly promote new adaptive trajectories such as zoonotic transfer or antimicrobial resistance. However, for this to occur requires gaps to align in barriers to recombination within a given time frame. Chief among these barriers is the physical separation of species with distinct ecologies in separate niches. Within the genus Campylobacter there are species with divergent ecologies, from rarely isolated single host specialists to multi-host generalist species that are among the most common global causes of human bacterial gastroenteritis. Here, by characterising these contrasting ecologies, we can quantify HGT among sympatric and allopatric species in natural populations. Analysing recipient and donor population ancestry among genomes from 30 Campylobacter species we show that cohabitation in the same host can lead to a 6-fold increase in HGT between species. This accounts for up to 30% of all SNPs within a given species and identifies highly recombinogenic genes with functions including host adaptation and antimicrobial resistance. As described in some animal and plant species, ecological factors are a major evolutionary force for speciation in bacteria and changes to the host landscape can promote partial convergence of distinct species through HGT.

microbiology↗

bioRxiv2021

Non-serotype 2 isolates from healthy pigs are a potential zoonotic reservoir of Streptococcus suis genetic diversity and antimicrobial resistance

Streptococcus suis is a leading cause of bacterial meningitis in SE Asia, with frequent zoonotic transfer to humans associated with close contact with pigs. A small number of invasive lineages are responsible for endemic infection in the swine industry causing considerable global economic losses. A lack of surveillance and a rising trend in clinical treatment failure has raised concerns of growing antimicrobial resistance (AMR) among invasive S. suis. The source-sink dynamics between healthy and disease isolates is poorly understood and, in this study, we sample and sequence a collection of isolates predominantly from healthy pigs in Chiang Mai province, Northern Thailand. Pangenome comparisons with a selection of invasive serotype 2 isolates identified increased genetic diversity and more frequent AMR carriage in isolates from healthy pigs. Multiple antimicrobial resistance genes were identified conferring resistance to aminoglycosides, lincosamides, tetracycline and macrolides. All isolates were non-susceptinle to three or more different antimicrobial classes, and 75% of non-serotype 2 isolates were non-susceptible to 6 or more classes (compared to 37.5% of serotype 2 isolates). Antimicrobial resistance genes were found on integrative and conjugative elements (ICE) previously observed in other species, suggesting mobile gene pool which can be accessed by invasive disease isolates. Significance statementThe zoonotic pathogen Streptococcus suis causes respiratory disease in pigs and is among the most common causative agents of human clinical bacterial meningitis in SE Asia. We collected isolates from farmed healthy pigs in Northern Thailand, representing a source population from which invasive isolates have recently emerged - linked to the pork production industry. Pangenome characterisation of the isolates revealed a reservoir of genetic diversity and antimicrobial resistance suggesting that One Health approaches may be beneficial in tackling the increase in antimicrobial resistance.

microbiology↗

bioRxiv2021

Repeated out-of-Africa expansions of Helicobacter pylori driven by replacement of deleterious mutations

Helicobacter pylori lives in the human stomach and has a population structure which resembles that of its host. However, H. pylori from Europe and the Middle East trace a substantially higher fraction of ancestry from modern African populations than the humans that carry them. Here, we used a collection of Afro-Eurasian H. pylori genomes to show that this African ancestry is due to at least three distinct admixture events. H. pylori from East Asia, which have undergone little admixture, have accumulated many more non-synonymous mutations than African strains. European and Middle Eastern bacteria have elevated African ancestry at the sites of these mutations compared to either non-segregating or synonymous sites, implying selection to remove them. We used simulations to show that demographic bottlenecks can lead to long-term segregation of deleterious mutations, despite high rates of homologous recombination, but that population fitness can be restored by migration of small numbers of bacteria from non-bottlenecked populations, leading to mosaic patterns of ancestry like that seen for H. pylori. We conclude that H. pylori have been able to spread repeatedly from Africa by outcompeting strains that carried deleterious mutations accumulated during the original out-of-Africa bottleneck.

evolutionary biology↗

bioRxiv2021

Cross-species evolutionary rewiring in the enteric bacterium Campylobacter

Significance StatementGenetic exchange among bacteria shapes the microbial world. From the acquisition of antimicrobial resistance genes to fundamental questions about the nature of bacterial species, this powerful evolutionary force has preoccupied scientists for decades. However, the mixing of genes between species rests on a paradox. On one hand, promoting adaptation by conferring novel functionality, on the other potentially introducing disharmonious gene combinations (negative epistasis) that will be selected against. Taking an interdisciplinary approach to analyse natural populations of the enteric bacteria Campylobacter, an ideal example of long-range admixture, we demonstrate that genes can independently transfer across species boundaries and rejoin in epistasis in a recipient genome. This challenges conventional ideas and highlights the possibility of single step evolution by saltation. AbstractRecombination of short DNA fragments via horizontal gene transfer (HGT) can both introduce beneficial alleles and create genomic disharmony through negative epistasis. For non-core (accessory) genes, the negative epistatic cost is likely to be minimal because the incoming genes have not co-evolved with the recipient genome. By contrast, for the core genome, interspecific recombination is expected to be rare because disruptive allelic replacement is likely to introduce negative epistasis. Why then is homologous recombination common in the core of bacterial genomes? To understand this enigma we take advantage of an exceptional model system, the common enteric pathogens Campylobacter jejuni and Campylobacter coli, that are known for very high magnitude interspecies gene flow in the core genome. As expected, HGT does indeed disrupt co-adapted allele pairings (negative epistasis). However, multiple HGT events enable recovery of the genomes co-adaption between introgressing alleles, even in core metabolism genes (e.g., formate dehydrogenase). These findings demonstrate that, even for complex traits, genetic coalitions can be decoupled, transferred and independently reinstated in a new genetic background - facilitating transition between fitness peaks. In this example, the two-step recombinational process is associated with C. coli that are adapted to the agricultural niche.

microbiology↗

bioRxiv2020

Antimicrobial resistant Salmonella spp. circulating in antibiotic-free organic pig farms of northern-Thailand

We investigated the prevalence of Salmonella circulating in local organic pig farms in northern Thailand and typed isolated clones to better understand the population structure of the underlying Salmonella contamination. In total, 112 samples from 11 organic pig farms were processed from October to December 2018. Salmonella were detected in 9 farms with an overall prevalence of 25.0% (28/112). Prevalence detected in fecal, feeder, and boot swab samples was found to be 32.7% (17/53), 17.7% (6/34), and 20.0% (5/25), respectively. Of the 28 positive strains, Seven Salmonella serotypes were identified, with S. Rissen being the most common (15/28; 53.6%). 89.3% (25/28), 78.6% (22/28) and 71.4% (20/28) of isolated Salmonella were resisted against tetracycline, ampicillin, and sulfamethoxazole-trimethoprim, respectively. From multilocus sequence typing (MLST) analysis, the phylogenetic tree suggests dissemination of specific clones within herds that share routes of pig transportation and point mutations in housekeeping genes within herds. A minimum spanning tree (MST) revealed that Salmonella contamination in organic pig farming is possibly linked with conventional farming. Based on the own results, strictly highly organic practices provide a safe alternative enhancing domestic consumer trust and improve public health safety.

molecular biology↗