- Volume 9, Issue 3, 2023
Volume 9, Issue 3, 2023
- Research Articles
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- Pathogens and Epidemiology
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Streptococcus canis genomic epidemiology reveals the potential for zoonotic transfer
More LessStreptococcus canis , a multi-host pathogen commonly isolated from dogs and cats, has been occasionally reported in severe cases of human infection. To address the gap in knowledge on its virulence and host tropism, we investigated S. canis genomic epidemiology and report the results of this analysis for the first time. We analysed 59 S . canis whole genome sequences originating from a variety of host species, comprising 39 newly sequenced isolates from UK sources, along with all (n=20) publicly available genomes. Antimicrobial resistance (AMR) phenotype was determined for all 39 available isolates. Genomes were screened for determinants of resistance and virulence. We created a core SNP phylogeny and compared strain clustering to multi-locus sequence typing (MLST) and S. canis M-like protein (SCM) typing. We investigated the dataset for signals of host adaptation using phylogenetic analysis, accessory genome clustering and pan-genome-wide association study analysis. A total of 23 % (9/39) of isolates exhibited phenotypic resistance to lincosamides, macrolides and/or tetracyclines. This was complemented by the identification of AMR-encoding genes in all genomes: tetracycline (tetO 14 %, 8/59; and tetM 7 %, 4/59) and lincosamide/macrolide (ermB, 7 %, 4/59). AMR was more common in human (36 %, 4/11) compared to companion animal (18 %, 5/28) isolates. We identified 19 virulence gene homologues, 14 of which were present in all strains analysed. In an S. canis strain isolated from a dog with otitis externa we identified a homologue of S. pyogenes superantigen SMEZ. The MLST and SCM typing schemes were found to be incapable of accurately representing core SNP-based genomic diversity of the S. canis population. No evidence of host adaptation was detected, suggesting the potential for inter-species transmission, including zoonotic transfer.
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- Evolution and Responses to Interventions
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Insights into the genomic evolution and the alkali tolerance mechanisms of Agaricus sinodeliciosus by comparative genomic and transcriptomic analyses
More LessAgaricus sinodeliciosus is a rare wild edible mushroom from northwest China, and grows naturally in mild saline-alkali soil, which is also unusual in mushrooms. A. sinodeliciosus represents a potential model organism for explaining saline-alkali tolerance mechanisms and revealing related physiological processes in mushrooms. Here, we provide a high-quality genome of A. sinodeliciosus. Comparative genomic analyses reveal A. sinodeliciosus has numerous changes to its genome organization after a solitary evolutionary history under saline-alkali environments, such as gene family contraction, retrotransposon expansion and rapid evolution of adaptative genes. Our saline and alkali tolerance tests show that mycelium growth and fruit body formation of this species are effected by mild alkalinity. Transcriptomic analyses reveal that genes involved in carbon and nitrogen utilization, cell stability and fruit body formation of A. sinodeliciosus could be activated under mildly alkaline conditions. In particular, the ‘starch and sucrose metabolism’, ‘biosynthesis of amino acids’ and ‘phenylpropanoid biosynthesis’ pathways are important for mildly alkaline tolerance of A. sinodeliciosus. Like plants and arbuscular mycorrhizal fungi, in the rot fungus A. sinodeliciosus, the biosynthesis of intracellular small molecules could be enhanced to counter osmotic and oxidative stresses caused by mild alkalinity, and the biosynthesis of monolignol could be suppressed to increase cell wall infiltrates under mildly alkaline conditions. This research provides an understanding of the genomic evolution and mechanisms of A. sinodeliciosus in tolerance to saline-alkali environments. The A. sinodeliciosus genome constitutes a valuable resource for evolutionary and ecological studies of Agaricus.
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Advantages of analysing both pairwise SNV-distance and differing SNVs between Mycobacterium tuberculosis isolates for recurrent tuberculosis cause determination
Endogenous reactivation and exogenous reinfection are two possible causes of recurrent tuberculosis (TB). However, in some cases, precise cause determination can be challenging. In this study, we used whole genome sequencing to determine pairwise SNV distances and detect differing SNVs in initial and subsequent isolates for recurrent TB cases when the first and second episodes were caused by Mycobacterium tuberculosis (Mtb) strains with an identical spoligotype pattern. In total, 104 Mtb isolates from 36 recurrent TB and 16 single TB episode patients were included in the study. Most isolate pairs belonged to the SIT1 (n=21), SIT42 (n=9), SIT53 (n=9), and SIT254 (n=7) spoligotypes, and in 27 cases, resistance to at least one anti-TB drug was found in either isolate. Drug susceptibility was more common in the recurrent TB patient cohort, and longitudinal single TB episode isolates were more prone to be drug-resistant (p=0.03), while the association between patient cohort and spoligotype was not statistically significant (p=0.07). The pairwise SNV-distance between the longitudinal single TB episode isolates was small (0-7 SNVs). Among the recurrent TB isolates, based on the high SNV-distance (38–273 SNVs), six reinfection cases (16.7%) were identified. This distance was small (<10 SNVs) in the remaining 30 isolate pairs. Further analysis of differing SNVs revealed that 22 (61.1%) cases could be classified as possible reactivation. Notably, despite the small distance of 2–7 SNVs, initial isolates of eight patients (22.2%) had several SNVs that were not found in the second isolates; therefore, these cases were classified as reinfection with a closely related Mtb strain. No statistically significant difference in the time interval between specimen collection in the reactivation and reinfection Mtb sample groups (p=0.13) or an association between recurrence cause and drug resistance status (p=0.62) or spoligotype (p=0.79) could be detected. The mycobacterial median mutation rate of longitudinal single TB episodes and possible reactivation isolate pairs (n=37) was 0.12 SNVs/genome/year (IQR 0-0.39), and in 18 cases (48.6%), it was equal to zero. No statistically significant differences in mutation rate were found between recurrent TB and longitudinal single TB episode isolates (p=0.087), drug-susceptible and resistant isolates (p=0.37) or isolates of Beijing and other genotype families (p=0.33). Furthermore, four cases of fluoroquinolone resistance development through the acquired SNVs in the gyrA gene were identified. To conclude, this study highlighted the complexity of recurrent episode cause determination and showed the usefulness of differing SNV identification in both Mtb isolates in such cases. Expected drug susceptibility was the only discriminative factor for recurrent TB episode-causing mycobacterial strains, while no differences between reactivation and reinfection sample groups could be identified.
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Rapid adaptations of Legionella pneumophila to the human host
Legionella pneumophila are host-adapted bacteria that infect and reproduce primarily in amoeboid protists. Using similar infection mechanisms, they infect human macrophages, and cause Legionnaires’ disease, an atypical pneumonia, and the milder Pontiac fever. We hypothesized that, despite the similarities in infection mechanisms, the hosts are different enough that there exist high-selective value mutations that would dramatically increase the fitness of Legionella inside the human host. By comparing a large number of isolates from independent infections, we identified two genes, mutated in three unrelated patients, despite the short duration of the incubation period (2–14 days). One is a gene coding for an outer membrane protein (OMP) belonging to the OmpP1/FadL family. The other is a gene coding for an EAL-domain-containing protein involved in cyclic-di-GMP regulation, which in turn modulates flagellar activity. The clinical strain, carrying the mutated EAL-domain-containing homologue, grows faster in macrophages than the wild-type strain, and thus appears to be better adapted to the human host. As human-to-human transmission is very rare, fixation of these mutations into the population and spread into the environment is unlikely. Therefore, parallel evolution – here mutations in the same genes observed in independent human infections – could point to adaptations to the accidental human host. These results suggest that despite the ability of L. pneumophila to infect, replicate in and exit from macrophages, its human-specific adaptations are unlikely to be fixed in the population.
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- Short Communications
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- Pathogens and Epidemiology
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Genomic surveillance identifies SARS-CoV-2 transmission patterns in local university populations, Wisconsin, USA, 2020–2022
Novel variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continue to emerge as the coronavirus disease 2019 (COVID-19) pandemic extends into its fourth year. Understanding SARS-CoV-2 circulation in university populations is vital for effective interventions in higher education settings and will inform public health policy during pandemics. In this study, we performed whole-genome sequencing of 537 of 1717 SARS-CoV-2-positive nasopharyngeal/nasal swab samples collected over a nearly 20-month period from two university populations in Wisconsin, USA. We observed that the viral sequences were distributed into 57 lineages/sub-lineages belonging to 15 clades, of which the majority were from 21K (omicron, 36.13 %) and 21J (delta, 30.91 %). Nearly 40 % (213) of the sequences were omicron, of which BA.1 and its eight descendent lineages accounted for 91 %, while the remaining belonged to BA.2 and its six descendent lineages. Independent analysis of the sequences from these two universities revealed significant differences in the circulating SARS-CoV-2 variants. Phylogenetic analysis of university sequences with a global sub-dataset demonstrated that the sequences of the same lineages from the university populations were more closely related. Genome-based analysis of closely related strains, along with phylogenetic clusters and mutational differences, identified that potential virus transmission occurred within and between universities, as well as between the university and the local community. Although this study improves our understanding of the distinct transmission patterns of circulating variants in local universities, expanding genomic surveillance capacity will aid local jurisdictions not only in identifying emerging SARS-CoV-2 variants, but also in improving data-driven public health mitigation and policy efforts.
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- Methods
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- Genomic Methodologies
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Palidis: fast discovery of novel insertion sequences
The diversity of microbial insertion sequences, crucial mobile genetic elements in generating diversity in microbial genomes, needs to be better represented in current microbial databases. Identification of these sequences in microbiome communities presents some significant problems that have led to their underrepresentation. Here, we present a bioinformatics pipeline called Palidis that recognizes insertion sequences in metagenomic sequence data rapidly by identifying inverted terminal repeat regions from mixed microbial community genomes. Applying Palidis to 264 human metagenomes identifies 879 unique insertion sequences, with 519 being novel and not previously characterized. Querying this catalogue against a large database of isolate genomes reveals evidence of horizontal gene transfer events across bacterial classes. We will continue to apply this tool more widely, building the Insertion Sequence Catalogue, a valuable resource for researchers wishing to query their microbial genomes for insertion sequences.
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