Rapid baso-apical translocation of Mycobacterium avium ssp. paratuberculosis in mammary epithelial cells in the presence of Escherichia coli

Modeling Paratuberculosis in Laboratory Animals, Cells, or Tissues: A Focus on Their Applications for Pathogenesis, Diagnosis, Vaccines, and Therapy Studies

Paratuberculosis is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. Paratuberculosis that affects a wide variety of domestic and wild animals. It is considered one of the diseases with the highest economic impact on the ruminant industry. Despite many efforts and intensive research, paratuberculosis control still remains controversial, and the existing diagnostic and immunoprophylactic tools have great limitations. Thus, models play a crucial role in understanding the pathogenesis of infection and disease, and in testing novel vaccine candidates. Ruminant animal models can be restricted by several reasons, related to space requirements, the cost of the animals, and the maintenance of the facilities. Therefore, we review the potential and limitations of the different experimental approaches currently used in paratuberculosis research, focusing on laboratory animals and cell-based models. The aim of this review is to offer a vision of the models that have been used, and what has been achieved or discovered with each one, so that the reader can choose the best model to answer their scientific questions and prove their hypotheses. Also, we bring forward new approaches that we consider worth exploring in the near future.

Longitudinal Changes in Milk Microorganisms in the First Two Months of Lactation of Primiparous and Multiparous Cows

The present experiment was carried out to analyze the longitudinal changes in milk microorganisms. For this purpose, milk samples were collected from 12 healthy cows (n = 96; six primiparous cows and six multiparous cows) at eight different time points. The characteristics and variations in microbial composition were analyzed by 16S rRNA gene high-throughput sequencing. In the primiparous group, higher and more stable alpha diversity was observed in transitional and mature milk compared with the colostrum, with no significant difference in alpha diversity at each time point in the multiparous group. Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota were the most dominant phyla, and Pseudomonas, UCG-005, Acinetobacter, Vibrio, Lactobacillus, Bacteroides, Serratia, Staphylococcus, and Glutamicibacter were the most dominant genera in both primiparous and multiparous cow milk. Some typically gut-associated microbes, such as Bacteroides, UCG-005, and Rikenellaceae_RC9_gut_group, etc., were enriched in the two groups. Biomarker taxa with the day in time (DIM) were identified by a random forest algorithm, with Staphylococcus showing the highest degree of interpretation, and the difference in milk microbiota between the two groups was mainly reflected in 0 d-15 d. Additionally, network analysis suggested that there were bacteria associated with the total protein content in milk. Collectively, our results disclosed the longitudinal changes in the milk microbiota of primiparous and multiparous cows, providing further evidence in dairy microbiology.

Research progress on the association between mastitis and gastrointestinal microbes in dairy cows and the effect of probiotics

Mastitis in dairy cows affects milk quality and thereby constrains the development of the dairy industry. A clear understanding of the pathogenesis of mastitis can help its treatment. Mastitis is caused by the invasion of pathogenic bacteria into the mammary gland through the mammary ducts. However, recent studies suggested that an endogenous entero-mammary pathway in dairy cattle might also be playing an important role in regulating mastitis. Also, probiotic intervention regulating host gut microbes has become an interesting tool to control mastitis. This review discusses the association of gastrointestinal microbes with mastitis and the mechanism of action of probiotics in dairy cows to provide new ideas for the management of mastitis in large-scale dairy farms.

The deletion of yeaJ gene facilitates Escherichia coli escape from immune recognition

Mammary gland-derived Escherichia coli (E. coli) is an important pathogen causing dairy cow mastitis. Mammary gland mucosal immunity against infectious E. coli mainly depends on recognition of pathogen-associated molecular patterns by innate receptors. Stimulator of interferon (IFN) gene (STING) has recently been the dominant mediator in reacting to bacterial intrusion and preventing inflammatory disorders. In this study, we firstly proved that diguanylate cyclase YeaJ relieves mouse mammary gland pathological damage by changing E. coli phenotypic and host STING-dependent innate immunity response. YeaJ decreases mammary gland circular vacuoles, bleeding and degeneration in mice. In addition, YeaJ participates in STING-IRF3 signaling to regulate inflammation in vivo. While in vitro, YeaJ decreases damage to macrophages (RAW264.7) but not to mouse mammary epithelial cells (EpH4-Ev). Consistent with the results in mouse mammary gland, yeaJ significantly activates STING/TBK1/IRF3 pathway in RAW264.7 as well. In conclusion, the deletion of yeaJ gene facilitates E. coli NJ17 escape from STING-dependent innate immunity recognition in vitro and in vivo. This study highlights a novel role for YeaJ in E. coli infection, which provides a better understanding of host-bacteria interactions and potential prophylactic strategies for infections. IMPORTANCE E. coli is the etiological agent of environmental mastitis in dairy cows, which cause massive financial losses worldwide. However, the pathophysiological role of yeaJ in the interaction between E. coli and host remains unclear. We found that YeaJ significantly influences various biological characteristics and suppresses severe inflammatory response as well as greater damage. YeaJ alleviates damage to macrophages (RAW264.7) and mouse mammary gland. Moreover, these effects of YeaJ are achieved at least partial by mediating the STING-IRF3 signaling pathway. In conclusion, the deletion of yeaJ gene facilitates E. coli NJ17 escape from STING-dependent innate immunity recognition in vitro and in vivo. This study is the basis for further research to better understand host-bacteria interactions and provides potential prophylactic strategies for infections.

Differences in the coinfective process of Staphylococcus aureus and Streptococcus agalactiae in bovine mammary epithelial cells infected by Mycobacterium avium subsp. paratuberculosis

The interactions between Mycobacterium avium subsp. paratuberculosis (MAP) and the causative agents of bovine mastitis are still relatively unknown. Still, it is suspected that they may contribute to the worsening and persistence of mastitis within the mammary epithelial cells. Considering the growing economic implications of paratuberculosis and subclinical mastitis in dairy herds, this study aimed to determine the coinfection interaction between MAP and S. aureus or S. agalactiae in bovine mammary epithelial cells (MAC-T) in an ex-vivo model. For this purpose, internalisation tests of MAP + S. aureus or MAP + S. agalactiae were performed in MAC-T cells for 10, 30 and 120 min. The qPCR was performed to quantify internalised MAP at the time of exposure. Colony-forming units were counted on BHI agar medium for internalised subclinical mastitis bacteria at each time of infection. Viability tests of MAC-T cells, using the lactate dehydrogenase assay, were performed. The results showed that in the MAC-T cells previously infected by MAP and subsequently by S. aureus, there was a rapid internalisation in the first 10 min, maintaining a higher number of internalised bacteria during all exposure times. Regarding MAP + S. agalactiae, there were no changes in the internalisation patterns. The amount of MAP remained constant at all times evaluated, and there was no compromise in the viability of MAC-T cells during the tests. Thus, the results demonstrate the existence of an interaction between MAP + S. aureus, favouring internalisation and being able to contribute to the persistence of subclinical mastitis in dairy herds.

Inhibition of Escherichia coli invasion into bovine mammary epithelial cells previously infected by Mycobacterium avium subsp. paratuberculosis

Background

The coinfection process of Escherichia coli, an etiological agent of clinical mastitis and Mycobacterium avium subsp. paratuberculosis (MAP), a non-mastitic etiological agent in the bovine mammary gland is not fully known.

Objective

Verify the ability of MAP to interfere with the invasion and translocation of E. coli in bovine mammary epithelial cell line (MAC-T).

Methods

For the invasion assay, MAC-T cells were challenged with MAP K10 for 2 h and then challenged with E. coli for 10, 30 and 120 min. For the translocation assay, the trans well plates were used and the challenge sequence was repeated as previously described. The amount of E. coli in the assays was determined by counting colony forming units (CFU) in Luria-Bertani medium. Quantitative real-time PCR was used to quantify MAP in MAC-T cells. To verify the viability of the MAC-T cells, the MTT assay was performed. MAP culture supernatant was also evaluated at different percentages for E. coli growth.

Results

Previous MAP infection in MAC-T cells inhibited E. coli invasion in 10, 30 and 120 min. No significant interference of MAP in the translocation of E. coli from the apical-basal direction was verified. Quantity of MAP DNA inside the MAC-T cells was statistically similar. Neither reduction in MAC-T cells viability was detected during the experiment nor MAP-released factor in the supernatant inhibited E. coli invasion.

Conclusion

These findings suggest that MAP-positive cows could be more resistant to E. coli infection, but when infected, could rapidly translocate E. coli to the subepithelial region.

Milk Microbiota: What Are We Exactly Talking About?

The development of powerful sequencing techniques has allowed, albeit with some biases, the identification and inventory of complex microbial communities that inhabit different body sites or body fluids, some of which were previously considered sterile. Notably, milk is now considered to host a complex microbial community with great diversity. Milk microbiota is now well documented in various hosts. Based on the growing literature on this microbial community, we address here the question of what milk microbiota is. We summarize and compare the microbial composition of milk in humans and in ruminants and address the existence of a putative core milk microbiota. We discuss the factors that contribute to shape the milk microbiota or affect its composition, including host and environmental factors as well as methodological factors, such as the sampling and sequencing techniques, which likely introduce distortion in milk microbiota analysis. The roles that milk microbiota are likely to play in the mother and offspring physiology and health are presented together with recent data on the hypothesis of an enteromammary pathway. At last, this fascinating field raises a series of questions, which are listed and commented here and which open new research avenues.