Biological Characteristics and Pathogenicity of Helcococcus ovis Isolated From Clinical Bovine Mastitis in a Chinese Dairy Herd

Pangenomic and biochemical analyses of Helcococcus ovis reveal widespread tetracycline resistance and a novel bacterial species, Helcococcus bovis

Helcococcus ovis (H. ovis) is an opportunistic bacterial pathogen of a wide range of animal hosts including domestic ruminants, swine, avians, and humans. In this study, we sequenced the genomes of 35 Helcococcus sp. clinical isolates from the uterus of dairy cows and explored their antimicrobial resistance and biochemical phenotypes in vitro. Phylogenetic and average nucleotide identity analyses classified four Helcococcus isolates within a cryptic clade representing an undescribed species, for which we propose the name Helcococcus bovis sp. nov. By establishing this new species clade, we also resolve the longstanding question of the classification of the Tongji strain responsible for a confirmed human conjunctival infection. This strain did not neatly fit into H. ovis and is instead a member of H. bovis. We applied whole genome comparative analyses to explore the pangenome, resistome, virulome, and taxonomic diversity of the remaining 31 H. ovis isolates. An overwhelming 97% of H. ovis strains (30 out of 31) harbor mobile tetracycline resistance genes and displayed significantly increased minimum inhibitory concentrations of tetracyclines in vitro. The high prevalence of mobile tetracycline resistance genes makes H. ovis a significant antimicrobial resistance gene reservoir in our food chain. Finally, the phylogenetic distribution of co-occurring high-virulence determinant genes of H. ovis across unlinked and distant loci highlights an instance of convergent gene loss in the species. In summary, this study showed that mobile genetic element-mediated tetracycline resistance is widespread in H. ovis, and that there is evidence of co-occurring virulence factors across clades suggesting convergent gene loss in the species. Finally, we introduced a novel Helcococcus species closely related to H. ovis, called H. bovis sp. nov., which has been reported to cause infection in humans.

Metagenomic profiling of viral and microbial communities from the pox lesions of lumpy skin disease virus and sheeppox virus-infected hosts

Introduction

It has been recognized that capripoxvirus infections have a strong cutaneous tropism with the manifestation of skin lesions in the form of nodules and scabs in the respective hosts, followed by necrosis and sloughing off. Considering that the skin microbiota is a complex community of commensal bacteria, fungi and viruses that are influenced by infections leading to pathological states, there is no evidence on how the skin microbiome is affected during capripoxvirus pathogenesis.

Methods

In this study, shotgun metagenomic sequencing was used to investigate the microbiome in pox lesions from hosts infected with lumpy skin disease virus and sheep pox virus.

Results

The analysis revealed a high degree of variability in bacterial community structures across affected skin samples, indicating the importance of specific commensal microorganisms colonizing individual hosts. The most common and abundant bacteria found in scab samples were Fusobacterium necrophorum, Streptococcus dysgalactiae, Helcococcus ovis and Trueperella pyogenes, irrespective of host. Bacterial reads belonging to the genera Moraxella, Mannheimia, Corynebacterium, Staphylococcus and Micrococcus were identified.

Discussion

This study is the first to investigate capripox virus-associated changes in the skin microbiome using whole-genome metagenomic profiling. The findings will provide a basis for further investigation into capripoxvirus pathogenesis. In addition, this study highlights the challenge of selecting an optimal bioinformatics approach for the analysis of metagenomic data in clinical and veterinary practice. For example, direct classification of reads using a kmer-based algorithm resulted in a significant number of systematic false positives, which may be attributed to the peculiarities of the algorithm and database selection. On the contrary, the process of de novo assembly requires a large number of target reads from the symbiotic microbial community. In this work, the obtained sequencing data were processed by three different approaches, including direct classification of reads based on k-mers, mapping of reads to a marker gene database, and de novo assembly and binning of metagenomic contigs. The advantages and disadvantages of these techniques and their practicality in veterinary settings are discussed in relation to the results obtained.

Uterine microbial ecology and disease in cattle: A review

Due to the critical contribution of the uterine-associated microbiota in reproductive health, physiology, and performance, culture-independent methods have been increasingly employed to unravel key aspects of microbial ecology in the uterus of cattle. Nowadays, we know that bacterial diversity is crucial to maintain uterine health, however, there is still no consensus on the exact composition of a healthy uterine microbiota (or eubiosis). Generally, loss of bacterial diversity (or dysbiosis) contributes to the development of uterine infections, associated with increased relative abundances of Bacteroides, Fusobacterium, Trueperella, and Porphyromonas. Uterine infections are highly prevalent and gravely influence the profitability of cattle operations, animal welfare, and public health. Thus, understanding the dynamics of uterine microbial ecology is essential to develop effective strategies focused on preventing and mitigating the adverse effects of uterine dysbiosis as well as assisting in the process of restoring the core, healthy uterine microbiota. The aim of this review is to summarize research conducted in the microbial ecology of bovine uteri. We discuss the origin of the uterine microflora of healthy cows and the factors influencing its composition. In addition, we review the biology of specific pathogens that are known to increase in abundance during the occurrence of uterine disease. Lastly, we provide an overview of the bacterial biofilm in the bovine endometrium, and we briefly summarize the rationale for the use of probiotics to prevent uterine disease in cattle.

Establishing Galleria mellonella as an invertebrate model for the emerging multi-host pathogen Helcococcus ovis

Helcococcus ovis (H. ovis) can cause disease in a broad range of animal hosts, including humans, and has been described as an emerging bacterial pathogen in bovine metritis, mastitis, and endocarditis. In this study, we developed an infection model that showed H. ovis can proliferate in the hemolymph and induce dose-dependent mortality in the invertebrate model organism Galleria mellonella (G. mellonella). We applied the model and identified H. ovis isolates with attenuated virulence originating from the uterus of a healthy post-partum dairy cow (KG38) and hypervirulent isolates (KG37, KG106) originating from the uterus of cows with metritis. Medium virulence isolates were also isolated (KG36, KG104) from the uterus of cows with metritis. A major advantage of this model is that a clear differentiation in induced mortality between H. ovis isolates was detected in just 48 h, resulting in an effective infection model able to identify virulence differences between H. ovis isolates with a short turnaround time. Histopathology showed G. mellonella employs hemocyte-mediated immune responses to H. ovis infection, which are analogous to the innate immune response in cows. In summary, G. mellonella can be used as an invertebrate infection model for the emerging multi-host pathogen Helcococcus ovis.

Sequencing and characterization of Helcococcus ovis: a comprehensive comparative genomic analysis of virulence

BACKGROUND

Helcococcus ovis (H. ovis) is an emerging bacterial pathogen that commonly causes opportunistic respiratory, mammary, and uterine infections across mammalian hosts. This study applied long- and short-read whole genome sequencing technologies to identify virulence factors in five H. ovis isolates with low, medium, and high virulence phenotypes.

RESULTS

The resulting assemblies contained one circular chromosome ranging from 1,744,566 to 1,850,083 bp in length and had a mean GC content of 27.6%. Phylogenetic and nucleotide identity analyses found low virulence strain KG38 to be part of a clade that forms an outgroup apart from the rest of the H. ovis taxon. Assembling the first complete genomes of the species revealed major genomic rearrangements in KG38. One to six prophage regions were identified in each genome. A novel pathogenicity island was found exclusively in the two high virulence strains (KG37 and KG104), along with two hypothetical transmembrane proteins designated as putative VFs. Finally, three zinc ABC transporters and three Type-II/IV secretion systems were identified as possible virulence determinants in this species. The low virulence strain KG38 has fewer intact paralogs of these operons in its genome compared to the higher virulence isolates, which strongly suggests a role in virulence. This strain is also missing four putative virulence factors (VFs) found in other isolates associated with adherence (collagen adhesin precursor), immune evasion (choline-binding protein A and a PspA-like hypothetical protein) and cell wall synthesis (glycerol-3-phosphate cytidylyltransferase).

CONCLUSIONS

In this study, we assembled reference-quality complete genomes for five H. ovis strains to identify putative virulence factors. Phylogenetic analyses of H. ovis isolates revealed the presence of a clade representing a potentially novel species within the genus Helcococcus. A novel pathogenicity island and two hypothetical transmembrane proteins were found exclusively in high-virulence strains. The identification of Zinc ABC transporters and Type-II/IV secretion systems as possible virulence determinants, along with the differences in operon content between the low and high virulence isolates, strongly suggests they also play a role in the bacterium's pathogenicity. Taken together, these findings are a valuable first step toward deciphering the pathogenesis of H. ovis infections.

Effects of 4-vinylcyclohexene diepoxide on the cell cycle, apoptosis, and steroid hormone secretion of goat ovarian granulosa cells

4-Vinylcyclohexene diepoxide (VCD) is a potentially hazardous industrial chemical that may enter a goat's body in various ways during industrial breeding. Ovarian granulosa cells (GCs) play a critical role in supporting follicle development and hormone synthesis. However, there are few studies on the effect of VCD on goat ovarian GCs. In this study, goat ovarian GCs were isolated and treated with VCD. The results showed that treatment with VCD increased the proportion of S phase and G2/M cells, but decreased the proportion of G1 phase. VCD treatment significantly inhibited the expression of cyclin A and cyclin-dependent kinase 2 (CDK2). But the expression levels of p21 and p27 were increased. VCD could induce an apparent increase in the proportion of apoptosis and the level of cleaved caspase 3. Treatment with VCD significantly reduced the progesterone and estrogen concentration in the medium in which goat ovarian GCs were cultured. Correspondingly, the expression level of steroidogenic acute regulatory protein (STAR) was significantly downregulated. Treatment with 0.25 and 0.5 mM VCD, the protein expression level of insulin-like growth factor 1 receptor (IGF1R) and Akt were significantly decreased. Moreover, treatment with 0.25 mM VCD significantly inhibited the phosphorylation of Akt. In conclusion, VCD exposure had cytotoxic effects such as decreased cell viability, disordered cell cycle, increased apoptosis, and interference with steroid hormone synthesis on goat GCs. These cytotoxic effects of VCD on goat GCs may be due to the downregulation of IGF1R and the inhibition of IGF1R/Akt signaling pathway.