A model of clinical endometritis in Holstein heifers using pathogenic Escherichia coli and Trueperella pyogenes

Shifts in uterine microbiome associated with pregnancy outcomes at first insemination and clinical cure in dairy cows with metritis

Objectives were to assess differences in uterine microbiome associated with clinical cure and pregnancy outcomes in dairy cows treated for metritis. Cows with metritis (reddish-brownish, watery, and fetid vaginal discharge) were paired with cows without metritis based on parity and days postpartum. Uterine contents were collected through transcervical lavage at diagnosis, five days later following antimicrobial therapy (day 5), and at 40 days postpartum. Uterine microbiome was assessed by sequencing the V4 hypervariable region of the 16S rRNA gene. Although alpha-diversity based on Chao1, Shannon, and inverse Simpson indexes at diagnosis did not differ between cows with and without metritis, disease was associated with differences in beta-diversity. Prevalence of Porphyromonas, Bacteroides, and Veillonella was greater in cows with metritis. Streptococcus, Sphingomonas, and Ureaplasma were more prevalent in cows without metritis. Differences in beta-diversity between cows with and without metritis persisted on day 5. Uterine microbiome was not associated with clinical cure. Richness and alpha-diversity, but not beta-diversity, of uterine microbiome 40 days postpartum were associated with metritis and pregnancy. No relationship between uterine microbiome and pregnancy outcomes was observed. Results indicate that factors other than changes in intrauterine bacterial community underlie fertility loss and clinical cure in cows with metritis.

WGS of intrauterine E. coli from cows with early postpartum uterine infection reveals a non-uterine specific genotype and virulence factors

Escherichia coli has been attributed to playing a major role in a cascade of events that affect the prevalence and severity of uterine disease in cattle. The objectives of this project were to (i) define the association between the prevalence of specific antimicrobial resistance and virulence factor genes in E. coli with the clinical status related to uterine infection, (ii) identify the genetic relationship between E. coli isolates from cows with diarrhea, with mastitis, and with and without metritis, and (iii) determine the association between the phenotypic and genotypic antimicrobial resistance identified on the E. coli isolated from postpartum cattle. Bacterial isolates (n = 148) were obtained from a larger cross-sectional study. Cows were categorized into one of three clinical groups before enrollment: metritis, cows with purulent discharge, and control cows. For genomic comparison, public genomes (n = 130) from cows with diarrhea, mastitis, and metritis were included in a genome-wide association study, to evaluate differences between the drug classes or the virulence factor category among clinical groups. A distinct E. coli genotype associated with metritis could not be identified. Instead, a high genetic diversity among the isolates from uterine sources was present. A virulence factor previously associated with metritis (fimH) using PCR was not associated with metritis. There was moderate accuracy for whole-genome sequencing to predict phenotypic resistance, which varied depending on the antimicrobial tested. Findings from this study contradict the traditional pathotype classification and the unique intrauterine E. coli genotype associated with metritis in dairy cows.IMPORTANCEMetritis is a common infectious disease in dairy cattle and the second most common reason for treating a cow with antimicrobials. The pathophysiology of the disease is complex and is not completely understood. Specific endometrial pathogenic Escherichia coli have been reported to be adapted to the endometrium and sometimes lead to uterine disease. Unfortunately, the specific genomic details of the endometrial-adapted isolates have not been investigated using enough genomes to represent the genomic diversity of this organism to identify specific virulence genes that are consistently associated with disease development and severity. Results from this study provide key microbial ecological advances by elucidating and challenging accepted concepts for the role of Intrauterine E. coli in metritis in dairy cattle, especially contradicting the existence of a unique intrauterine E. coli genotype associated with metritis in dairy cows, which was not found in our study.

Microbial responses and changes in metabolic products in bovine uteri infected with Staphylococcus aureus

There is mounting evidence that the uterine microbiota has an important role in the pathogenesis of endometritis, with invasion of pathogenic bacteria being a main cause of uterine microbial imbalance. However, mechanisms of uterine microbiota resistance to pathogen invasion remain unclear. In this study, an intrauterine infusion of Staphylococcus aureus was used as a bovine endometritis model; it significantly increased abundance of pathogenic bacteria (Streptococcus, Helccoccus, Fusobacterium, and Escherichia-Shigella) and significantly decreased abundance of probiotics (Allstipes, Bacteroides, Phascolarctobacterium, Romboutsia, and Prevotella). In addition, the metabolite aloe-emodin was positively correlated with Prevotella and based on combined analyses of omics and probiotics, the presence of its metabolite aloe-emodin in the uterus at least partially resisted Staphylococcus aureus invasion. Therefore, Aloe-emodin has potential for regulating microbial structure and preventing endometritis.

Interferon-tau protects bovine endometrial epithelial cells against inflammatory injury by regulating the PI3K/AKT/β-catenin/FoxO1 signaling axis

Endometritis is one of the most common causes of infertility in dairy cows, and is histopathologically characterized by inflammation and damage of endometrial epithelium. Interferon-tau (IFN-τ) is a novel type I interferon secreted by ruminant trophoblast cells with low cytotoxicity even at high doses. Previous studies suggested that IFN-τ plays an important role in inflammation. However, the mechanisms whereby IFN-τ may modulate the inflammatory responses in the bovine endometrium are unknown. In the present study, primary bovine endometrial epithelial cells (BEEC) isolated from fresh and healthy uterine horns were used for in vitro studies. The integrity of BEEC was assessed by immunofluorescence staining for cytokeratin 18 (CK-18, a known epithelial marker). For the experiments, BEEC were stimulated with different concentrations of lipopolysaccharide (LPS; 0-20 µg/mL) for different times (0-24 h). Cell viability and apoptosis were assessed via CCK-8 and flow cytometry. In a preliminary study, we observed that compared with the control group without LPS, 10 µg/mL of LPS stimulation for 24 h induced apoptosis. In a subsequent study, 20 or 40 ng/mL of IFN-τ alleviated LPS-induced apoptosis. Relative to the LPS group, western blotting further revealed that IFN-τ inhibited the protein abundance of TLR4 and phosphorylated (p-) p65 (p-p65) and Bax/Bcl-2 ratio, suggesting that IFN-τ can protect BEEC against inflammatory injury. Furthermore, the protein abundance of p-phosphoinositide 3-kinase (p-PI3K), p-protein kinase B (p-AKT), p-glycogen synthase kinase-3β (p-GSK3β), β-catenin, and p-forkhead box O1 (p-FoxO1) was lower in the LPS group, whereas IFN-τ upregulated their abundance. The use of LY294002, a specific inhibitor of PI3K/AKT, attenuated the upregulation of p-PI3K, p-AKT p-GSK3β, β-catenin, and p-FoxO1 induced by IFN-τ, and also blocked the downregulation of TLR4, p-p65, and Bax/Bcl-2 ratio. This suggested that the inhibition of TLR4 signaling by IFN-τ was mediated by the PI3K/AKT pathway. Furthermore, compared with the LPS group, the β-catenin agonist SB216763 led to greater p-FoxO1 and lower p-p65 and cell apoptosis. In contrast, knockdown of β-catenin using small interfering RNA had the opposite effects. To explore the role of FoxO1 on the inhibition of TLR4 by IFN-τ, we employed LY294002 to inhibit the PI3K/AKT while FoxO1 was knocked down. Results revealed that the knockdown of FoxO1 blocked the upregulation of TLR4 and p-p65 induced by LY294002, and enhanced the inhibition of IFN-τ on TLR4, p-p65, and cell apoptosis. Overall, these findings confirmed that IFN-τ can protect endometrial epithelial cells against inflammatory injury via suppressing TLR4 activation through the regulation of the PI3K/AKT/β-catenin/FoxO1 axis. These represent new insights into the molecular mechanisms underlying the anti-inflammatory function of IFN-τ in BEEC, and also provide a theoretical basis for further studies on the in vivo application of IFN-τ to help prevent negative effects of endometritis.

Induced endometrial inflammation compromises conceptus development in dairy cattle†

Endometrial inflammation is associated with reduced pregnancy per artificial insemination (AI) and increased pregnancy loss in cows. It was hypothesized that induced endometritis alters histotroph composition and induces inflammatory signatures on conceptus that compromise development. In Experiment 1, lactating cows were assigned to control (CON; n = 23) or to an intrauterine infusion of Escherichia coli and Trueperella pyogenes (ENDO; n = 34) to induce endometritis. Cows received AI 26 days after treatment, and the uterine fluid and conceptuses were collected on day 16 after AI. In Experiment 2, Holstein heifers were assigned to CON (n = 14) or ENDO (n = 14). An embryo was transferred on day 7 of the estrous cycle, and uterine fluid and conceptuses were recovered on day 16. Composition of histotroph and trophoblast and embryonic disc gene expression were assessed. Bacterial-induced endometritis in lactating cows altered histotroph composition and pathways linked to phospholipid synthesis, cellular energy production, and the Warburg effect. Also, ENDO reduced conceptus length in cows and altered expression of genes involved in pathogen recognition, nutrient uptake, cell growth, choline metabolism, and conceptus signaling needed for maternal recognition of pregnancy. The impact of ENDO was lesser on conceptuses from heifers receiving embryo transfer; however, the affected genes and associated pathways involved restricted growth and increased immune response similar to the observed responses to ENDO in conceptuses from lactating cows. Bacterial-induced endometrial inflammation altered histotroph composition, reduced conceptus growth, and caused embryonic cells to activate survival rather than anabolic pathways that could compromise development.

Evaluation of blood serum iron concentration as an alternative biomarker for inflammation in dairy cows

This study aimed to clarify the relationship between acute phase protein (APP) concentrations and serum Fe concentrations to determine whether serum iron (Fe) can be clinically applied as a substitute for APPs in cows. One hundred five Holstein-Friesian breed lactating dairy cows were enrolled in this study. Cows with inflammatory diseases were 16 subclinical, and 15 severe mastitis cows, in addition to 15 mild and 16 severe sole ulcer cows. The plasma haptoglobin (HPT), alpha-1 acid glycoprotein (AGP), SAA, serum Fe levels, and other biochemical parameters in the cows were measured. The two-sample t-tests and multiple logistic regression analysis were used to compare the control and inflammatory disease groups. ROC analysis was used to evaluate the ability to diagnose inflammation disease. From the results, the proposed diagnostic cutoff value for plasma SAA and serum Fe concentrations to identify dairy cows with inflammatory diseases based on analyses of ROC curves were set at > 3.65 mg/l and < 120.50 µg/dl, respectively. Therefore, instead of using expensive inflammatory markers to evaluate the inflammatory state at the first treatment day for inflammatory diseases in cow, it shows the useful for screening with serum Fe concentration that can be measured easily and inexpensively as alternative inflammatory biomarkers.

Relationship of peripartum inflammation with reproductive health in dairy cows

Failure of a robust but well-regulated immune response may result in reproductive tract inflammatory disease, such as metritis, purulent vaginal discharge, or endometritis. Metritis is consistently associated with reduced diversity of the uterine microbiome. Similarly, purulent vaginal discharge at 4 to 6 wk postpartum is strongly associated with bacterial infection of the uterus. Conversely, the microbiome of healthy cows and those with subclinical endometritis is generally similar, so endometritis is thought to be a consequence of dysregulation of inflammation rather than changes in uterine microbiota. There is an emerging concept that inflammation is not only a reaction to injury or disease but that it can be a consequence of or precursor to metabolic disturbances. The degree of systemic inflammation is associated with the level of trauma and bacterial contamination of the uterus or mammary gland, the degree of fat mobilization and release of nonesterified fatty acids, and perhaps leaky gut, all of which result in the release of proinflammatory cytokines. Therefore, uterine inflammation may be exacerbated by systemic inflammation, but may also contribute to heightened systemic inflammation in transition cows. However, clarity and progress are limited by a lack of validated criteria to quantify systemic inflammation and to identify its sources.

Review: Postpartum reproductive disease and fertility in dairy cows

This paper reviews recent data and concepts on metritis, purulent vaginal discharge (PVD), and endometritis in dairy cows and the ways in which these diseases affect reproductive performance. Metritis is characterized by fetid discharge from the uterus, with or without fever. Purulent vaginal discharge describes exudate that is >50% pus that may be attributable to uterine infection or cervicitis. Endometritis is inflammation of the uterus diagnosed by endometrial cytology with a proportion of neutrophils (typically ≥5%) that is associated with impaired fertility. Metritis and PVD are associated with uterine bacterial dysbiosis: changes in the microbiota to lesser diversity and greater abundance of pathogens, especially Gram-negative anaerobic bacteria, and Trueperella pyogenes in the case of PVD. Metritis is justifiably treated with approved antibiotics but criteria for more selective treatment without loss of performance are emerging. Purulent vaginal discharge is not synonymous with clinical endometritis, and greater precision in terminology is warranted. PVD is likely under-diagnosed and represents an opportunity for improved management in many herds. Endometritis seems in many cases to reflect persistent, dysregulated inflammation, for which the inciting cause is unclear. Postpartum uterine infection and inflammation have harmful effects on oocytes, embryo development, and the endometrium for at least three months, even if the disease is apparently resolved. Emerging concepts of the resolution and regulation of inflammation are promising for the improvement of prevention and therapy of endometritis.

Induced endometritis in early lactation compromises production and reproduction in dairy cows

Objectives of this experiment were to study the effect of infusing utero-pathogenic bacteria to induce endometrial inflammation on productive performance in early lactation and subsequent reproduction. Although endometritis is associated with perturbed reproduction, numerous factors may contribute to the observed association. It was hypothesized that induced endometrial inflammation, resulting in localized and systemic inflammatory responses, compromises production and reproduction. Holstein cows without clinical disease and with less than 18% polymorphonuclear leukocytes (PMN) in endometrial cytology on d 31 ± 3 postpartum had their estrous cycle synchronized. Cows were blocked by parity and genomic breeding value for cow conception rate and, within block, assigned randomly to remain as untreated controls (CON; n = 37) or to receive an intrauterine infusion of 5.19 × 10⁸ cfu Escherichia coli and 4.34 × 10⁸ cfu Trueperella pyogenes during the luteal phase to induce endometrial inflammation (INF; n = 48). Endometrial cytology was taken on d 2 and 7 after treatment to evaluate the proportion of PMN. Rectal temperature, dry matter intake, and yields of milk and components were measured in the first 7 d after treatment. Blood serum was analyzed for concentration of haptoglobin. Leukocytes were isolated from blood on d 2 and 7 after treatment and on d 19 after artificial insemination (AI) and mRNA was quantified for a select group of genes. Cows received AI and reproduction was followed for 300 d postpartum. Bacterial infusion induced endometrial inflammation with increased proportions of PMN in the endometrial cytology on d 2 (4.4 ± 0.7 vs. 26.3 ± 2.8%) and 7 (10.9 ± 1.7 vs. 17.4 ± 2.1%) after treatment, resulting in increased mean prevalence of subclinical endometritis (>10% PMN; 23.3 ± 6.3 vs. 80.9 ± 5.1%). Rectal temperature did not differ between CON and INF, but the concentration of haptoglobin in serum tended to increase in INF compared with CON (113 ± 14 vs. 150 ± 16 µg/mL). Induced endometrial inflammation reduced yields of milk (44.9 ± 0.8 vs. 41.6 ± 0.8 kg/d), protein (1.19 ± 0.03 vs. 1.12 ± 0.03 kg/d), and lactose (2.17 ± 0.04 vs. 2.03 ± 0.04 kg/d) and tended to reduce dry matter intake (20.7 ± 0.5 vs. 19.4 ± 0.6 kg/d) in the first 7 d after treatment. Indeed, the reduction in milk yield lasted 4 wk. However, treatment did not affect yields of energy-corrected milk or fat because treatment with INF increased the concentration of fat in milk (3.54 ± 0.10 vs. 3.84 ± 0.10%). Induced endometrial inflammation reduced pregnancy per AI at all inseminations (33.4 ± 5.1 vs. 21.6 ± 3.7%) and the hazard of pregnancy (0.61; 95% CI = 0.36-1.04), which extended the median days open by 24 d. Blood leukocytes from INF cows had increased mRNA expression of the pro-inflammatory gene IL1B on d 2 and 7 after treatment, but reduced expression of the IFN-stimulated genes ISG15 and MX2 on d 19 after AI. Induced endometrial inflammation depressed production and caused long-term negative effects on reproduction in lactating dairy cows.

Prepartum heat stress in dairy cows increases postpartum inflammatory responses in blood of lactating dairy cows

Uterine diseases and heat stress (HS) are major challenges for the dairy cow. Heat stress alters host immune resilience, making cows more susceptible to the development of uterine disease. Although HS increases the incidence of uterine disease, the mechanisms by which this occurs are unclear. We hypothesize that evaporative cooling (CL) to alleviate HS in prepartum cows has carry-over effects on postpartum innate immunity. Nulliparous pregnant Holstein heifers were assigned to receive either forced CL that resulted in cool conditions (shade with water soakers and fans; n = 14) or to remain under HS conditions (barn shade only; n = 16) for 60 d prepartum. Postpartum, all cows were housed in a freestall barn equipped with shade, water soakers, and fans. Respiratory rate and rectal temperature during the prepartum period were greater in HS heifers compared with CL heifers, indicative of HS. Although milk production was decreased in HS cows compared with CL cows, the incidence of uterine disease and content of total or pathogenic bacteria in vaginal mucus on d 7 or d 21 postpartum was not affected by treatment. Whole blood was collected on d 21 and subjected to in vitro stimulation with lipopolysaccharide. Lipopolysaccharide-induced accumulation of IL-1β, IL-10, and MIP-1α was greater in blood collected from HS cows compared with CL cows. Our results imply that prepartum HS during late pregnancy has carry-over effects on postpartum innate immunity, which may contribute to the increased incidence of uterine disease observed in cows exposed to prepartum HS.

Dynamics and Diversity of Intrauterine Anaerobic Microbiota in Dairy Cows with Clinical and Subclinical Endometritis

The aim of the study was to characterize the dynamics of anaerobic cultivable postpartum microbiota in the uterus of dairy cows. In total, 122 dairy cows were enrolled and sampled on day 0 (day of calving) and on days 3, 9, 15, 21, and 28 postpartum (pp). Samples were cultivated anaerobically and analyzed by MALDI-TOF MS. In total, 1858 isolates were recovered. The most prevalent facultative anaerobic genera were Trueperella (27.8%), Streptococcus (25.4%), and Escherichia (13.1%). The most prevalent obligate anaerobes were Peptoniphilus (9.3%), Bacteroides (3.3%), and Clostridium (2.4%). The microbial communities were highly dynamic and diverse. On the animal level, Trueperella pyogenes on day 21 and 28 pp was associated with clinical endometritis, and E. coli on day 21 pp was associated with subclinical endometritis. The occurrence of Streptococcus pluranimalium on day 28 was related to uterine health. The presence of T. pyogenes, Streptococcus, and Peptoniphilus was significantly associated with an increased risk for purulent vaginal discharge. Primiparous cows showed a higher prevalence of T. pyogenes, Fusobacterium necrophorum, Porphyromonas levii, and Peptoniphilus spp. than multiparous cows but were not more susceptible to uterine diseases. This study might provide a suitable basis for future co-cultivation studies to elucidate potential synergistic interactions between microbiota.

Autophagy Mediates Escherichia Coli-Induced Cellular Inflammatory Injury by Regulating Calcium Mobilization, Mitochondrial Dysfunction, and Endoplasmic Reticulum Stress

Bovine endometritis is a reproductive disorder that is induced by mucus or purulent inflammation of the uterine mucosa. However, the intracellular control chain during inflammatory injury remains unclear. In the present study, we found that E. coli activated the inflammatory response through the assembly of the NLRP3 inflammasome and activation of the NF-κB p65 subunit in primary bovine endometrial epithelial cells (bEECs). Infection with E. coli also led to an abnormal increase in cytoplasmic calcium and mitochondrial dysfunction. Additionally, live-cell imaging of calcium reporters indicated that the increase in cytosolic calcium mainly was caused by the release of Ca²⁺ ions stored in the ER and mitochondria, which was independent of extracellular calcium. Cytoplasmic calcium regulates mitochondrial respiratory chain transmission, DNA replication, and biogenesis. Pretreatment with NAC, BAPTA-AM, or 2-APB reduced the expression of IL-1β and IL-18. Moreover, ERS was involved in the regulation of bovine endometritis and cytosolic calcium was an important factor for regulating ERS in E. coli-induced inflammation. Finally, activation of autophagy inhibited the release of IL-1β and IL-18, cytochrome c, ATP, ERS-related proteins, and cytoplasmic calcium. Collectively, our findings demonstrate that autophagy mediated E. coli-induced cellular inflammatory injury by regulating cytoplasmic calcium, mitochondrial dysfunction, and ERS.

Baogong decoction treats endometritis in mice by regulating uterine microbiota structure and metabolites

Endometritis is persistent inflammation caused by bacteria, which can lead to infertility. Although traditional Chinese medicine (TCM) has been used to treat endometritis, the underlying mechanism is still unclear. Here, Baogong Decoction (BGD), a TCM compound, was used to treat mouse endometritis induced by Escherichia coli (E. coli), and then 16S rRNA sequencing and non-targeted metabolomics were used to investigate the change of uterine microbiota and metabolomes in serum and uterine after BGD treatment. Finally, the therapeutic effect of potential metabolites for treating mouse endometritis screened by combined omics analyses was verified using pathological model. The results showed that BGD treatment could effectively treat endometritis associated with the increasing relative abundance of Firmicutes, Bacteroides, Lactobacillus and Lactococcus, and the decreasing relative abundance of Cupriavidus and Proteobacteria. 133 and 130 metabolites were found to be potential biomarkers in serum and uterine tissue respectively. In serum and tissues, dehydroepiandrosterone (DHEA) and catechol were significantly increased in the BGD treatment versus the inflammation group. Results of combined omics analyses demonstrated that DHEA was positively correlated with changes in microbiota. Results of pathological model demonstrated that DHEA could cure endometritis effectively associated with the decreasing infiltration of inflammatory cells and expression of inflammatory factors in the uterus. In summary, our results demonstrated that BGD could cure endometritis in mice by modulating the structure of the uterine microbiota and its metabolites, in which DHEA may be one of the main components of the therapeutic effect of BGD.

Cortisol inhibits lipopolysaccharide-induced inflammatory response in bovine endometrial stromal cells via NF-κB and MAPK signaling pathways

Bovine uterine infection is commonly caused by Escherichia coli (E. coli). Elevated concentrations of plasma cortisol have been reported in postpartum cows. However, the direct role of cortisol in the inflammatory response of bovine endometrial stromal cells (BESCs) remains unclear. Therefore, the aim of the study was to explore the regulatory effect of cortisol on lipopolysaccharide (LPS)-induced inflammatory response in BESCs. Both the primary and immortalized BESCs were used in this study. BESCs were treated with cortisol (5, 15, and 30 ng/mL) in the presence of LPS. The mRNA expression of inflammatory cytokines and chemokines was detected using RT-qPCR. Western blot and immunofluorescence were used to analyze the activation of the NF-κB and MAPK signaling pathways. The results revealed that cortisol downregulated the LPS-induced overexpression of interleukin(IL)-1β, IL-6, IL-8, TNF-α, COX-2, iNOS in BESCs. Moreover, cortisol inhibited LPS-induced phosphorylation levels of IκB, p65, ERK1/2, JNK and p38, and p65 nuclear translocation in BESCs. These results indicated that cortisol inhibited LPS-induced inflammatory response in BESCs, which may be mediated by suppressing the NF-κB and MAPK signaling pathways.

The Expression and Bioinformatics Analysis of Circular RNAs in Endometritis Mouse Uterus Tissues

Previous studies have shown that circular RNAs are directly or indirectly involved in the occurrence of various diseases by regulating gene expression. However, the acting mechanism of circular RNAs in endometritis remains unclear. In this study, we successfully established an endometritis model in mouse using Escherichia coli; endometrial integrity was destroyed, inflammatory cells infiltrated and the expression of IL-6, IL-1β, TNF-α was significantly up-regulated. We analyzed and screened the circular RNA expression profiles between healthy and endometritis-stricken mice by the Illumina HiSeq platform, and used qRT-PCR method to verify the different expressions of circular RNAs. Gene ontology (GO) analysis showed that circular RNAs were mainly involved in biological processes such as the positive regulation of transcription from RNA polymerase POL II promoter and the negative regulation of cell proliferation. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of circular RNAs target genes may be involved in the TGF-β signaling pathway. We verified the expression of TGF-β and its related factors; the mRNA of TGF-β1 and smad7 were significantly up-regulated in endometritis mouse (p < 0.01) and the protein expression level of p-smad3 was significantly decreased (p < 0.01). Finally, we constructed a circular RNAs−miRNA network to elucidate the potential regulatory relationship between two small molecules. This research may provide new ideas for circular RNAs in the treatment of endometritis.

Anti-inflammatory effects of progesterone through NF-κB and MAPK pathway in lipopolysaccharide- or Escherichia coli-stimulated bovine endometrial stromal cells

Postpartum uterine infection in dairy cows is commonly caused by pathogenic bacteria such as Escherichia coli (E. coli). Progesterone elicits immunosuppressive function within bovine endometrium, and has been suggested to be related to postpartum uterine infection. Endometrial stroma is exposed to bacteria due to the disruption of epithelium during parturition, but the effect and mechanism of progesterone on innate immune response of stromal cells has not been reported. This study evaluated the impact of progesterone on inflammatory response of primary endometrial stromal cells stimulated by lipopolysaccharide or heat-killed E. coli. Quantitative PCR analysis revealed that progesterone repressed mRNA induction of IL1B, IL6, TNF, CXCL8, NOS2, and PTGS2 in stromal cells in response to lipopolysaccharide or E. coli challenge. Consistently, Western blot and immunofluorescence staining results showed that progesterone suppressed lipopolysaccharide- or E. coli-induced MAPK and NF-κB activations characterized with decreased phosphorylations of ERK1/2, JNK, P38, IκBα, and P65, and inhibition of P65 nuclear translocation. In unstimulated stromal cells, progesterone alone did not affect the mRNA transcription for IL6, TNF, CXCL8, NOS2, and PTGS2, and the signaling cascade of MAPK and NF-κB, but decreased IL1B mRNA expression. These results revealed that the anti-inflammatory effect of progesterone in lipopolysaccharide- or E. coli-challenged endometrial stromal cells was probably mediated through MAPK and NF-κB pathways.

Antibiotic resistance and phylogenetic profiling of Escherichia coli from dairy farm soils; organic versus conventional systems

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First known comparison of antimicrobial resistance traits in E. coli strains from new zealand farms practicing organic and conventional husbandry.

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Potential extended spectrum β-lactamase producing strains isolated from dairy farm environments.

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Organic dairy farms tended to harbour fewer resistant isolates than those recovered from conventionally farmed counterparts.

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Evidence for anthroponotic transmission of resistant strains of human origin to farm environments.

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Implications for the spread of antimicrobial resistance traits from farm environments discussed.

The prevalence and spread of antimicrobial resistance (AMR) as a result of the persistent use and/or abuse of antimicrobials is a key health problem for health authorities and governments worldwide. A study of contrasting farming systems such as organic versus conventional dairy farming may help to authenticate some factors that may contribute to the prevalence and spread of AMR in their soils. A case study was conducted in organic and conventional dairy farms in the South Canterbury region of New Zealand.

A total of 814 dairy farm soil E. coli (DfSEC) isolates recovered over two years were studied. Isolates were recovered from each of two farms practicing organic, and another two practicing conventional husbandries. The E. coli isolates were examined for their antimicrobial resistance (AMR) against cefoxitin, cefpodoxime, chloramphenicol, ciprofloxacin, gentamicin, meropenem, nalidixic acid, and tetracycline. Phylogenetic relationships were assessed using an established multiplex PCR method. The AMR results indicated 3.7% of the DfSEC isolates were resistant to at least one of the eight selected antimicrobials. Of the resistant isolates, DfSEC from the organic dairy farms showed a lower prevalence of resistance to the antimicrobials tested, compared to their counterparts from the conventional farms. Phylogenetic analysis placed the majority (73.7%) of isolates recovered in group B1, itself dominated by isolates of bovine origin. The tendency for higher rates of resistance among strains from conventional farming may be important for future decision-making around farming practices Current husbandry practices may contribute to the prevalence and spread of AMR in the industry.

Effect of intrauterine infusion of two cephalosporins, ceftazidime and cephapirin, on uterine bacterial load and uterine horn diameter in bovine subclinical endometritis

This study aimed to evaluate the effect of intrauterine infusion of ceftazidime and cephapirin on uteri­ne bacterial load and uterine horn diameter in bovine subclinical endometritis. At 7-8 weeks postpartum, a total of 122 cows suffering from subclinical endometritis were divided into three groups. Group I cows were intrauterinely (IU) infused with 2 g ceftazidime diluted with 50 mL saline; group II cows were IU infused with 2 g cephapirin diluted with 50 mL saline; and group III cows were kept as untreated control. Vaginal examination, ultrasonography and bacterial examination were done before treatment programme and later repeated twice at 10-day intervals. Staphylococcus spp., Klebsiella spp., Streptococcus spp., Escherichia coli and Proteus spp. were isolated. After the end of the treatment programme, proportions of cows infected with Staphylococcus spp. and Streptococcus spp. were significantly (P<0.05) decreased in ceftazidime and cephapirin groups. However, proportions of cows infected with Escherichia coli were significantly (P<0.05) decreased in the ceftazidime group only. Uterine bacterial loads in ceftazidime and cephapirin groups were significantly decreased (P<0.05). Mean uterine horn diameters in ceftazidime group (2.44±0.03 cm) became significantly lower (P<0.05) than those in cephapirin (2.70±0.04 cm) and control (3.06±0.06 cm) groups. Conception rate in ceftazidime group (80.95%) was significantly (P<0.05) higher than rates recorded in cephapirin (64.00%) and control (26.67%) groups. In conclusion, ceftazidime and cephapirin decreased uterine bacterial load. Moreover, ceftazidime significantly reduced uterine horn diameter compared to the other groups and was associated with significantly higher conception rate. Thus, ceftazidime is recommended for treatment of subclinical endometritis in dairy cows.

Tanshinone ⅡA inhibits the lipopolysaccharide-induced epithelial-mesenchymal transition and protects bovine endometrial epithelial cells from pyolysin-induced damage by modulating the NF-κB/Snail2 signaling pathway

Mixed infection with Escherichia coli and Trueperella pyogenes (T. pyogenes) leads to purulent endometritis, but the underlying molecular mechanisms remain unclear. The aim of this study was to investigate the effect of tanshinone ⅡA (Tan ⅡA) on E. coli and T. pyogenes -induced purulent endometritis and explore the underlying mechanism. First, lipopolysaccharide (LPS) isolated from E. coli and bacteria-free filtrates (BFFs) isolated from T. pyogenes were used to induce a model of bovine endometrial epithelial cell (bEEC) damage in vitro. bEECs were pretreated with or without Tan ⅡA for 2 h, before LPS and BFFs were introduced to induce damage to investigate the protective effect of Tan IIA. Then, the cytolytic activity and inflammatory response in bEECs were examined using CCK-8, LDH and RT-qPCR assays. Furthermore, we confirmed the molecular mechanism by which Tan ⅡA reversed the damaged phenotypes in LPS- and BFFs-induced bEECs via the NF-κB/Snail2 pathway using qPCR and Western blotting. Tan ⅡA significantly decreased the cytolytic activity and inflammatory response in LPS- and BFFs-induced bEECs. In addition, Tan ⅡA reversed the dysregulation of E-cadherin, N-cadherin and vimentin. Moreover, Tan ⅡA significantly inhibited the activation of the NF-κB signaling pathway and decreased the expression level of Snail2, which is the main regulator of the epithelial-mesenchymal transition (EMT). In summary, Tan ⅡA inhibits the LPS-induced EMT and protects bEECs from pyolysin-induced damage by modulating the NF-κB/Snail2 signaling pathway.

Development of an intrauterine infection model in the postpartum dairy cow

AIMS

To develop an intrauterine infection model for Trueperella pyogenes in postpartum dairy cows and to assess the effect of this infection on the degree of intrauterine inflammation and concentrations of progesterone in serum.

METHODS

The oestrous cycles of 36 healthy, non-pregnant, postpartum dairy cows were synchronised. They were then treated by intrauterine infusion of 0.5 g cephapirin before being blocked by age and randomly assigned to treatment with intrauterine infusion of saline (n = 18), 10⁷ (n = 9) or 10⁹ (n = 9) cfu of T. pyogenes, approximately 4 days after the expected time of ovulation (Day 0). Prior to intrauterine infusion on Day 0 and again on Days 3, 7, 10, and 15, cytobrush samples were collected from the uterus of each cow for microbiology and assessment of the percentage of polymorphonuclear neutrophils (PMN%). Blood samples were collected on the same days for measurement of concentrations of progesterone in serum, and uterine lumen diameter was assessed daily using transrectal ultrasonography.

RESULTS

Trueperella pyogenes was isolated from 5/18 (28%), 7/9 (78%) and 8/9 (89%) cows infused with saline, 10⁷ or 10⁹ cfu of T. pyogenes, respectively (p < 0.001). Mean PMN% in the control cows did not change over time (p > 0.05), whereas it was higher on Days 7 and 10 than Day 0 in the 10⁷ cfu group, and higher on Days 3 and 10 than Day 0 in the 10⁹ cfu group (p < 0.05). The percentage of observations with uterine lumen diameters >2 mm was higher in cows infused with 10⁷ (29.3 (95% CI = 14.5-44.2)%) or 10⁹ cfu (19.2 (95% CI = 7.0-31.5)%) than in control cows (3.1 (95% CI = 0.1-6.0)%) (p < 0.001). Mean concentrations of progesterone in serum were higher in cows infused with 10⁷ cfu (2.01 (SE 0.19) ng/mL) than cows infused with 10⁹ cfu (1.01 (SE 0.27) ng/mL), with the control group intermediate (1.41 (SE 0.19) ng/mL) (p = 0.03).

CONCLUSIONS

Infusion of 10⁷ or 10⁹ cfu of T. pyogenes resulted in the establishment of intrauterine infection in 83% of cows. Infection resulted in increased uterine lumen diameter, and an inflammatory response, i.e. elevated PMN%.

CLINICAL RELEVANCE

This intrauterine infection model may be useful for future research on, for example, the pathogenesis of intrauterine infection in postpartum dairy cows.

Uterine infection alters the transcriptome of the bovine reproductive tract three months later

Infection of the postpartum uterus with pathogenic bacteria is associated with infertility months later in dairy cattle. However, it is unclear whether these bacterial infections lead to long-term changes in the reproductive tract that might help explain this infertility. Here we tested the hypothesis that infusion of pathogenic bacteria into the uterus leads to changes in the transcriptome of the reproductive tract 3 months later. We used virgin Holstein heifers to avoid potential confounding effects of periparturient problems, lactation, and negative energy balance. Animals were infused intrauterine with endometrial pathogenic bacteria Escherichia coli and Trueperella pyogenes (n = 4) and compared with control animals (n = 6). Three months after infusion, caruncular and intercaruncular endometrium, isthmus and ampulla of the oviduct, and granulosa cells from ovarian follicles >8 mm diameter were profiled by RNA sequencing. Bacterial infusion altered the transcriptome of all the tissues when compared with control. Most differentially expressed genes were tissue specific, with 109 differentially expressed genes unique to caruncular endometrium, 57 in intercaruncular endometrium, 65 in isthmus, 298 in ampulla, and 83 in granulosa cells. Surprisingly, despite infusing bacteria into the uterus, granulosa cells had more predicted upstream regulators of differentially expressed genes than all the other tissues combined. In conclusion, there were changes in the transcriptome of the endometrium, oviduct and even granulosa cells, 3 months after intrauterine infusion of pathogenic bacteria. These findings imply that long-term changes throughout the reproductive tract could contribute to infertility after bacterial infections of the uterus.

Aucubin ameliorates the LPS-induced inflammatory response in bovine endometrial epithelial cells by inhibiting NF-κB and activating the Keap1/Nrf2 signalling pathway

Cows are susceptible to pathogenic bacterial infection after pregnancy, leading to inflammation of the endometrium. Aucubin (AU) has been proven to exhibit highly effective anti-inflammatory activity, but its ability to protect against endometritis in dairy cows remains unclear. Therefore, the goal of the present study was to evaluate the protective effect of AU on the LPS-induced inflammatory response of bovine endometrial epithelial cells (BEECs). After pre-treating BEECs with AU (10, 20 and 50 μM) for 6 hr, the cells were stimulated with LPS for 3 hr. Subsequently, BEECs apoptosis was analysed by flow cytometry, the expression of pro-inflammatory cytokine mRNA was detected by qRT-PCR, and changes in NF-κB and Keap1/Nrf2 signalling were analysed by western blotting and immunofluorescence analyses. The results showed that AU can reduce TNF-α, IL-1β, IL-6, COX-2 and iNOS mRNA expression in BEECs and reduce cell apoptosis. Furthermore, AU significantly reduced the level of NF-κB p65 and IκB phosphorylation and inhibited the nuclear translocation of NF-κB p65. AU also activated the Keap1/Nrf2 pathway, promoting the nuclear transfer of Nrf2 and increasing Keap1, Nrf2, HO-1 and NQO1 mRNA and protein levels. Taken together, these results indicate that AU ameliorates the LPS-induced inflammatory response by inhibiting NF-κB and activating the Keap1/Nrf2 signalling pathway, which has a protective effect on BEECs.

MicroRNA-Mediated Gene Regulatory Mechanisms in Mammalian Female Reproductive Health

Mammalian reproductive health affects the entire reproductive cycle starting with the ovarian function through implantation and fetal growth. Various environmental and physiological factors contribute to disturbed reproductive health status leading to infertility problems in mammalian species. In the last couple of decades a significant number of studies have been conducted to investigate the transcriptome of reproductive tissues and organs in relation to the various reproductive health issues including endometritis, polycystic ovarian syndrome (PCOS), intrauterine growth restriction (IUGR), preeclampsia, and various age-associated reproductive disorders. Among others, the post-transcriptional regulation of genes by small noncoding miRNAs contributes to the observed transcriptome dysregulation associated with reproductive pathophysiological conditions. MicroRNAs as a class of non-coding RNAs are also known to be involved in various pathophysiological conditions either in cellular cytoplasm or they can be released to the extracellular fluid via membrane-bounded extracellular vesicles and proteins. The present review summarizes the cellular and extracellular miRNAs and their association with the etiology of major reproductive pathologies including PCOS, endometritis, IUGR and age-associated disorders in various mammalian species.

Trueperella pyogenes pyolysin inhibits lipopolysaccharide-induced inflammatory response in endometrium stromal cells via autophagy- and ATF6-dependent mechanism

Trueperella pyogenes (T. pyogenes) is a common opportunistic pathogen of many livestock and play an important regulation role during multibacterial infection and interaction with the host by its primary virulence factor pyolysin (PLO). The purpose of this study was to investigate the regulation role of PLO which serve as a combinational pathogen with lipopolysaccharide (LPS) during endometritis. In this study, the expression of bioactive recombinant PLO (rPLO) in a prokaryotic expression system and its purification are described. Moreover, we observed that rPLO inhibited the innate immune response triggered by LPS and that methyl-β-cyclodextrin (MBCD) abrogated this inhibitory effect in goat endometrium stromal cells (gESCs). Additionally, we show from pharmacological and genetic studies that rPLO-induced autophagy represses gene expression by inhibiting NLRP3 inflammasome activation. Importantly, this study reported that ATF6 serves as a primary regulator of the cellular inflammatory reaction to rPLO. Overall, these observations suggest that T. pyogenes PLO could create an immunosuppressive environment for other pathogens invasion by regulating cellular signaling pathways.

Uterine infusion of bacteria alters the transcriptome of bovine oocytes

Postpartum uterine infection reduces fertility in dairy cattle; however, the mechanisms of uterine infection-mediated infertility are unknown. Paradoxically, infection-induced infertility persists after the resolution of disease. Oocytes are a finite resource, which are present at various stages of development during uterine infection. It is likely that oocyte development is influenced by uterine infection-induced changes to the follicular microenvironment. To better understand the impact of infection on oocyte quality we employed global transcriptomics of oocytes collected from heifers after receiving intrauterine infusion of pathogenic Escherichia coli and Trueperella pyogenes. We hypothesized that the oocyte transcriptome would be altered in response to intrauterine infection. A total of 452 differentially expressed genes were identified in oocytes collected from heifers 4 days after bacteria infusion compared to vehicle infusion, while 539 differentially expressed genes were identified in oocytes collected from heifers 60 days after bacteria infusion. Only 42 genes were differentially expressed in bacteria-infused heifers at both Day 4 and Day 60. Interferon, HMGB1, ILK, IL-6, and TGF-beta signaling pathways were downregulated in oocytes collected at Day 4 from bacteria-infused heifers, while interferon, ILK, and IL-6 signaling were upregulated in oocytes collected at Day 60 from bacteria-infused heifers. These data suggest that bacterial infusion alters the oocyte transcriptome differently at Day 4 and Day 60, suggesting different follicle stages are susceptible to damage. Characterizing the long-term impacts of uterine infection on the oocyte transcriptome aids in our understanding of how infection causes infertility in dairy cattle.

Experimentally Induced Endometritis Impairs the Developmental Capacity of Bovine Oocytes†

Uterine infection is associated with infertility in women and dairy cows, even after the resolution of infection. However, the mechanisms causing this persistent infertility are unclear. Here, we hypothesized that induced endometritis in non-lactating dairy cows would reduce the developmental competence of oocytes. Non-lactating Holstein cows received an intrauterine infusion of endometrial pathogenic bacteria (Escherichia coli and Trueperella pyogenes; n = 12) or vehicle control (n = 11) on day 2 of the estrous cycle. Bacterial infusion increased expression of endometrial inflammatory mediators, and a mucopurulent discharge in the vagina confirmed the establishment of endometritis. Oocytes were collected by transvaginal ultrasound-guided ovum pickup on days 2, 24, 45, and 66 following infusion and subjected to in vitro fertilization and embryo culture. Bacterial infusion resulted in fewer cleaved oocytes developing to morulae compared to vehicle-infused controls (30.7 versus 45.0%), with the greatest effect observed in oocytes collected on day 24. Development to morula was inversely correlated with endometrial expression of IL6 on day 6. The expression of genes associated with embryo quality did not differ significantly between morulae from bacteria-infused and control cows. Artificial insemination 130 days after intrauterine infusion resulted in normal, filamentous embryos that produced interferon tau 16 days after conception in both infusion groups. This model of experimentally induced uterine infection successfully resulted in endometritis and a reduction in the proportion of oocytes that developed to morulae following in vitro fertilization. In conclusion, endometritis reduced the capacity of oocytes to develop to morulae.

Anti-inflammatory Effect of Astragalin and Chlorogenic Acid on Escherichia coli-Induced Inflammation of Sheep Endometrial Epithelium Cells

Endometritis is one of the main diseases which harm sheep husbandry. Astragalin and chlorogenic acid (CGA) are common active ingredients of traditional Chinese medicine (TCM) with immunoprotective, antioxidant, and anti-inflammatory properties. In the present study, sheep endometrial epithelium cells (SEECs) were successfully purified and identified, and the in vitro inflammation model of SEECs induced by Escherichia coli (E. coli) was successfully established. To explore the effect of astragalin and CGA on the inflammation induced by E. coli and its potential mechanism, six groups were set up, namely, group C, M, astragalin, CGA, BAY, and STR. Cells in group C were incubated with DMEM/F12 for 6 h, while cells in group M, astragalin, CGA, BAY, and STR were incubated with DMEM/F12, astragalin, CGA, BAY, and STR for 3 h, respectively, followed by E. coli infection at a multiplicity of infection (MOI) of 1 E. coli per cell for 3 h. Subsequently, the cells and the supernatant were collected to detect the expression of genes in the toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) pathway by ELISA, qPCR, and western blot. The results showed that E. coli could induce inflammation of SEECs in vitro, while astragalin and CGA could alleviate the inflammatory response induced by E. coli via inhibiting the activation of the TLR4/NF-κB signaling pathway, which provides a theoretical and experimental foundation for preventing sheep endometritis clinically.

Cortisol inhibits the Escherichia coli-induced endometrial inflammatory response through NF-κB and MAPK pathways in postpartum goats

Glucocorticoids have been widely used as anti-inflammatory therapies. The mechanisms of cortisol action in goat does with endometritis, however, have not been reported. The aim of this study was to investigate the mechanism of cortisol in modulation of effects of E. coli-induced endometritis in the does. Does (n = 24) were assigned to four groups (n = 6): control, E. coli, cortisol, and E. coli + cortisol groups. Does in the cortisol and E. coli + cortisol group were treated with cortisol from 3 days before E. coli inoculations occurred to 36 days post-partum. Does in the E. coli and inoculation groups were administered via intrauterine infusion E. coli O₅₅ (10⁹ CFU/mL) at 0 h. Physical indicators, macroscopic and microscopic changes in the endometrium, uterine secretion cytology and bacteriology were evaluated before (0 h) and at 6, 12, 24, 48, and 72 h after E. coli inoculation. The TLR4 and pro-inflammatory cytokine mRNA transcripts were detected using qPCR. The activations of NF-κB and MAPK signaling pathways were detected using Western blot procedures. As a result, cortisol inhibited the inflammatory response of does by reducing the clinical symptoms, morphological endometrial damage, % PMN in uterine secretions, relative abundance of inflammatory gene mRNA transcripts in the endometrium of does. Cortisol inhibited NF-κB activity by reducing MyD88 and IκB phosphorylation. Treatment with cortisol suppressed the phosphorylation of ERK1/2, p38MAPK, and JNK. These results indicate the anti-inflammatory effect of cortisol in the endometrium of does may be regulated by NF-κB and MAPK pathways.

Preventing postpartum uterine disease in dairy cattle depends on avoiding, tolerating and resisting pathogenic bacteria

Up to forty percent of dairy cows develop metritis or endometritis when pathogenic bacteria infect the uterus after parturition. However, resilient cows remain healthy even when exposed to the same pathogens. Here, we provide a perspective on the mechanisms that dairy cows use to prevent postpartum uterine disease. We suggest that resilient cows prevent the development of uterine disease using the three complementary defensive strategies of avoiding, tolerating and resisting infection with pathogenic bacteria. Avoidance maintains health by limiting the exposure to pathogens. Avoidance mechanisms include intrinsic behaviors to reduce the risk of infection by avoiding pathogens or infected animals, perhaps signaled by the fetid odor of uterine disease. Tolerance improves health by limiting the tissue damage caused by the pathogens. Tolerance mechanisms include neutralizing bacterial toxins, protecting cells against damage, enhancing tissue repair, and reprogramming metabolism. Resistance improves health by limiting the pathogen burden. Resistance mechanisms include inflammation driven by innate immunity and adaptive immunity, with the aim of killing and eliminating pathogenic bacteria. Farmers can also help cows prevent the development of postpartum uterine disease by avoiding trauma to the genital tract, reducing stress, and feeding animals appropriately during the transition period. Understanding the mechanisms of avoidance, tolerance and resistance to pathogens will inform strategies to generate resilient animals and prevent uterine disease.

TREM-1 deficiency attenuates the inflammatory responses in LPS-induced murine endometritis

Endometritis, which is usually caused by bacterial infection, is characterized by high levels of pro-inflammatory cytokines and a high infertility rate. Triggering receptor expressed on myeloid cells-1 (TREM-1) has been recognized as a potent amplifier of inflammatory reactions. Studies have demonstrated reduced inflammatory responses and mortality rates of animals with bacterial infection due to the blocking of TREM-1 expression. However, whether TREM-1 deficiency could alleviate the inflammatory reaction in bacterial endometritis is still unclear. Here, TREM-1 knock-out (Trem-1-/- ) mice were used to inhibit TREM-1 signalling to evaluate its role in inflammatory reactions after a highly pathogenic LPS infection in mice uteri. The results demonstrated that TREM-1 deficiency attenuated the inflammation in mice uteri; markedly reduced the number of polymorphonuclear neutrophils; and suppressed interleukin-1β (IL-1β), IL-6, and tumour necrosis factor-α (TNF-α) concentrations in serum as well as their production in inflamed uteri after LPS stimulation. Our results illustrate an anticipated pathogenic impact of TREM-1 on endometritis during LPS infection and indicate that blocking of TREM-1 in LPS-induced endometritis holds considerable promise for blunting excessive inflammation.

Symposium review: The uterine microbiome associated with the development of uterine disease in dairy cows

Until 2010, our knowledge of the uterine microbiome in cows that developed uterine disease relied almost exclusively on culture-dependent studies and mostly included cows with clinical endometritis (i.e., with purulent uterine discharge). Those studies consistently found a strong positive correlation between Trueperella pyogenes and clinical endometritis, whereas other pathogens such as Escherichia coli, Fusobacterium necrophorum, Prevotella melaninogenica, and Bacteroides spp. were also commonly cocultured. In contrast, Streptococcus spp., Staphylococcus spp., and Bacillus spp. were usually isolated from healthy cows. Starting in 2010, culture-independent studies using PCR explored the microbiome of cows with metritis and clinical endometritis, and observed that E. coli was a pioneer pathogen that predisposed cows to infection with F. necrophorum, which was strongly associated with metritis, and to infection with T. pyogenes, which was strongly associated with clinical endometritis. Starting in 2011, culture-independent studies using metagenomic sequencing expanded our knowledge of the uterine microbiome. It has been shown that cows have bacteria in the uterus even before calving, they have an established uterine microbiome within 20 min of calving, and that the microbiome structure is identical between cows that develop metritis and healthy cows until 2 d postpartum, after which the bacterial structure of cows that developed metritis deviates in favor of greater relative abundance of Bacteroidetes and Fusobacteria and lesser relative abundance of Proteobacteria and Tenericutes. The shift in the uterine microbiome in cows that develop metritis is characterized by a loss of heterogeneity and a decrease in bacterial richness. At the genus level, Bacteroides, Porphyromonas, and Fusobacterium have the strongest association with metritis. At the species level, we observed that Bacteroides pyogenes, Porphyromonas levii, and Helcococcus ovis were potential emerging uterine pathogens. Finally, we have shown that the hematogenous route is a viable route of uterine infection with uterine pathogens. Herein, we propose that metritis is associated with a dysbiosis of the uterine microbiota characterized by decreased richness, and an increase in Bacteroidetes and Fusobacteria, particularly Bacteroides, Porphyromonas, and Fusobacterium.