Shielding Effect of Escherichia coli O-Antigen Polysaccharide on J5-Induced Cross-Reactive Antibodies

Immunology of the Bovine Mammary Gland: Advances in Recent Years

Bovine mastitis remains the most costly disease in the dairy industry due to its impact on milk production, milk quality, and animal welfare. Optimal immunity is essential for the mammary gland to resist infections, efficiently clear them, and limit damage to mammary tissue. This article highlights recent advancements built on previous knowledge exploring opportunities for enhancing mammary gland immune responses. Ultimately, these improvements aim to increase the resistance of the mammary gland to infections and reduce the costs associated with this disease in the dairy industry.

Alternative treatment candidates to antibiotic therapy for bovine mastitis in the post-antibiotic era: a comprehensive review

Mastitis, an inflammation of mammary tissue frequently associated with infection, is a prevalent disease among dairy animals. Bacterial intra-mammary infection is identified as a primary cause of bovine mastitis (BM). In dairy cattle, antimicrobials are used for mastitis treatment during the lactating phase and for dry cow therapy. Although self-curing can occur, the success of mastitis treatment depends on several factors, including the type of bacteria responsible for the infection, the effectiveness of the administered antibiotics, and the host's overall immune response. Moreover, the growing resistance of microorganisms to antibiotics has restricted the available treatment options for managing intramammary infections. In addition, the utilization of critically essential antimicrobials in animals raised for food production may elevate the risk of human infections that are challenging to treat. Therefore, it is crucial to have alternative treatments with equivalent or superior effectiveness as part of any stewardship program. These may include the application of nanotechnology, stem cell technology, photodynamic and laser radiation or the use of traditional herbal medical plants, nutraceuticals, antibacterial peptides, bacteriocins, antibodies therapy, bacteriophages, phage lysins, and probiotics as alternatives to antibiotics. This review aims to discuss the potential of vaccination as an indirect strategy, along with nanotechnology, probiotics, stem cell therapy, antimicrobial peptides, photodynamic therapy, laser irradiation, and antibody treatments as direct approaches. These approaches are examined as possible alternative therapeutic options to antibiotic treatment for BM.

Invited review: Mastitis Escherichia coli strains-Mastitis-associated or mammo-pathogenic?

Bovine mastitis remains a major concern for dairy farmers, mainly because of its effect on the economy of their activity and on animal welfare. Because Escherichia coli is considered a major mastitis pathogen, the diversity of E. coli strains isolated from mastitis cases has been studied for decades, with the aim to discover new ways to fight this infection. With the recent advances in whole-genome sequencing, a detailed view of the peculiarities of mastitis E. coli strains has emerged. This review aims to bring together the knowledge garnered over the years with the more recent results of whole-genome analyses. Whereas the concept of a mammary pathogenic E. coli has been proposed, because a common set of virulence genes cannot be identified among mastitis E. coli strains, we prefer the use of mastitis-associated E. coli (MAEC), with MAEC being more an "ecotype" rather than a "pathotype." Indeed, data available so far suggest that a common feature of MAEC would rather be an enrichment in fitness capabilities that makes them well-suited for survival and rapid adaptation to changing biotopes in the mammary gland, which we qualify as intramammary ecotopes.

A novel vaccine strategy using quick and easy conversion of bacterial pathogens to unnatural amino acid-auxotrophic suicide derivatives

We propose a novel strategy for quick and easy preparation of suicide live vaccine candidates against bacterial pathogens. This method requires only the transformation of one or more plasmids carrying genes encoding for two types of biological devices, an unnatural amino acid (uAA) incorporation system and toxin-antitoxin systems in which translation of the antitoxins requires the uAA incorporation. Escherichia coli BL21-AI laboratory strains carrying the plasmids were viable in the presence of the uAA, whereas the free toxins killed these strains after the removal of the uAA. The survival time after uAA removal could be controlled by the choice of the uAA incorporation system and toxin-antitoxin systems. Multilayered toxin-antitoxin systems suppressed escape frequency to less than 1 escape per 109 generations in the best case. This conditional suicide system also worked in Salmonella enterica and E. coli clinical isolates. The S. enterica vaccine strains were attenuated with a >105 fold lethal dose. Serum IgG response and protection against the parental pathogenic strain were confirmed. In addition, the live E. coli vaccine strain was significantly more immunogenic and provided greater protection than a formalin-inactivated vaccine. The live E. coli vaccine was not detected after inoculation, presumably because the uAA is not present in the host animals or the natural environment. These results suggest that this strategy provides a novel way to rapidly produce safe and highly immunogenic live bacterial vaccine candidates.

IMPORTANCE

Live vaccines are the oldest vaccines with a history of more than 200 years. Due to their strong immunogenicity, live vaccines are still an important category of vaccines today. However, the development of live vaccines has been challenging due to the difficulties in achieving a balance between safety and immunogenicity. In recent decades, the frequent emergence of various new and old pathogens at risk of causing pandemics has highlighted the need for rapid vaccine development processes. We have pioneered the use of uAAs to control gene expression and to conditionally kill host bacteria as a biological containment system. This report proposes a quick and easy conversion of bacterial pathogens into live vaccine candidates using this containment system. The balance between safety and immunogenicity can be modulated by the selection of the genetic devices used. Moreover, the uAA-auxotrophy can prevent the vaccine from infecting other individuals or establishing the environment.

Bacterial Virus Forcing of Bacterial O-Antigen Shields: Lessons from Coliphages

In most Gram-negative bacteria, outer membrane (OM) lipopolysaccharide (LPS) molecules carry long polysaccharide chains known as the O antigens or O polysaccharides (OPS). The OPS structure varies highly from strain to strain, with more than 188 O serotypes described in E. coli. Although many bacteriophages recognize OPS as their primary receptors, these molecules can also screen OM proteins and other OM surface receptors from direct interaction with phage receptor-binding proteins (RBP). In this review, I analyze the body of evidence indicating that most of the E. coli OPS types robustly shield cells completely, preventing phage access to the OM surface. This shield not only blocks virulent phages but also restricts the acquisition of prophages. The available data suggest that OPS-mediated OM shielding is not merely one of many mechanisms of bacterial resistance to phages. Rather, it is an omnipresent factor significantly affecting the ecology, phage-host co-evolution and other related processes in E. coli and probably in many other species of Gram-negative bacteria. The phages, in turn, evolved multiple mechanisms to break through the OPS layer. These mechanisms rely on the phage RBPs recognizing the OPS or on using alternative receptors exposed above the OPS layer. The data allow one to forward the interpretation that, regardless of the type of receptors used, primary receptor recognition is always followed by the generation of a mechanical force driving the phage tail through the OPS layer. This force may be created by molecular motors of enzymatically active tail spikes or by virion structural re-arrangements at the moment of infection.

Evaluation of immunogenicity of enterobactin conjugate vaccine for the control of Escherichia coli mastitis in dairy cows

Mastitis is the most common disease of dairy cows that incurs severe economic losses to the dairy industry. Currently, environmental mastitis pathogens are a major problem for most dairy farms. A current commercially available Escherichia coli vaccine does not prevent clinical mastitis and production losses, likely due to antibody accessibility and antigenic variation issues. Therefore, a novel vaccine that prevents clinical disease and production losses is critically needed. Recently a nutritional immunity approach, which restricts bacterial iron uptake by immunologically sequestering conserved iron-binding enterobactin (Ent), has been developed. The objective of this study was to evaluate the immunogenicity of the keyhole limpet hemocyanin-enterobactin (KLH-Ent) conjugate vaccine in dairy cows. Twelve pregnant Holstein dairy cows in their first through third lactations were randomized to the control or vaccine group, with 6 cows per group. The vaccine group received 3 subcutaneous vaccinations of KLH-Ent with adjuvants at drying off (D0), 20 (D21), and 40 (D42) days after drying off. The control group was injected with phosphate-buffered saline (pH 7.4) mixed with the same adjuvants at the same time points. Vaccination effects were assessed over the study period until the end of the first month of lactation. The KLH-Ent vaccine did not cause any systemic adverse reactions or reduction in milk production. Compared with the control group, the vaccine elicited significantly higher levels of serum Ent-specific IgG at calving (C0) and 30 d postcalving (C30), mainly its IgG2 fraction, which was significantly higher at D42, C0, C14, and C30 d, with no significant change in IgG1 levels. Milk Ent-specific IgG and IgG2 levels in the vaccine group were significantly higher on C30. Fecal microbial community structures were similar for both control and vaccine groups on the same day and shifted directionally along the sampling days. In conclusion, the KLH-Ent vaccine successfully triggered strong Ent-specific immune responses in dairy cows without significantly affecting the gut microbiota diversity and health. The results show that Ent conjugate vaccine is a promising nutritional immunity approach in control of E. coli mastitis in dairy cows.

Semisynthetic Glycoconjugate Vaccine Candidates against Escherichia coli O25B Induce Functional IgG Antibodies in Mice

Extraintestinal pathogenic Escherichia coli (ExPEC) is a major health concern due to emerging antibiotic resistance. Along with O1A, O2, and O6A, E. coli O25B is a major serotype within the ExPEC group, which expresses a unique O-antigen. Clinical studies with a glycoconjugate vaccine of the above-mentioned O-types revealed O25B as the least immunogenic component, inducing relatively weak IgG titers. To evaluate the immunological properties of semisynthetic glycoconjugate vaccine candidates against E. coli O25B, we here report the chemical synthesis of an initial set of five O25B glycan antigens differing in length, from one to three repeat units, and frameshifts of the repeat unit. The oligosaccharide antigens were conjugated to the carrier protein CRM₁₉₇. The resulting semisynthetic glycoconjugates induced functional IgG antibodies in mice with opsonophagocytic activity against E. coli O25B. Three of the oligosaccharide-CRM₁₉₇ conjugates elicited functional IgGs in the same order of magnitude as a conventional CRM₁₉₇ glycoconjugate prepared with native O25B O-antigen and therefore represent promising vaccine candidates for further investigation. Binding studies with two monoclonal antibodies (mAbs) revealed nanomolar anti-O25B IgG responses with nanomolar K _D values and with varying binding epitopes. The immunogenicity and mAb binding data now allow for the rational design of additional synthetic antigens for future preclinical studies, with expected further improvements in the functional antibody responses. Moreover, acetylation of a rhamnose residue was shown to be likely dispensable for immunogenicity, as a deacylated antigen was able to elicit strong functional IgG responses. Our findings strongly support the feasibility of a semisynthetic glycoconjugate vaccine against E. coli O25B.

Escherichia coli Mastitis in Dairy Cattle: Etiology, Diagnosis, and Treatment Challenges

Bovine mastitis is an inflammation of the udder tissue parenchyma that causes pathological changes in the glandular tissue and abnormalities in milk leading to significant economic losses to the dairy industry across the world. Mammary pathogenic Escherichia (E.) coli (MPEC) is one of the main etiologic agents of acute clinical mastitis in dairy cattle. MPEC strains have virulence attributes to resist the host innate defenses and thrive in the mammary gland environment. The association between specific virulence factors of MPEC with the severity of mastitis in cattle is not fully understood. Furthermore, the indiscriminate use of antibiotics to treat mastitis has resulted in antimicrobial resistance to all major antibiotic classes in MPEC. A thorough understanding of MPEC’s pathogenesis and antimicrobial susceptibility pattern is required to develop better interventions to reduce mastitis incidence and prevalence in cattle and the environment. This review compiles important information on mastitis caused by MPEC (e.g., types of mastitis, host immune response, diagnosis, treatment, and control of the disease) as well as the current knowledge on MPEC virulence factors, antimicrobial resistance, and the dilemma of MPEC as a new pathotype. The information provided in this review is critical to identifying gaps in knowledge that will guide future studies to better design diagnostic, prevent, and develop therapeutic interventions for this significant dairy disease.

Construction of the waaF Subunit and DNA Vaccine Against Escherichia coli in Cow Mastitis and Preliminary Study on Their Immunogenicity

Escherichia coli (E. coli) is one of the major pathogenic bacteria in bovine mastitis, which usually triggers systemic symptoms by releasing lipopolysaccharide (LPS). waaF is the core in LPS pathogenicity. In this study, a new waaF vaccine candidate was identified, constructed with the pcDNA3.1 (+)HisB-waaF plasmid to create to a DNA vaccine (pcwaaF), and transfected into MCF-7 cells to produce recombinant waaF subunit vaccine (rwaaF). After that, the safety of the two vaccine candidates was evaluated in mouse model. Immunogenicity and mortality of challenged mice were compared in 20 and 40 μg per dose, respectively. The results showed that rwaaF and pcwaaF were successfully constructed and the complete blood count and serum biochemical indicated that both of the vaccine candidates were safe (p > 0.05). In addition, histopathological staining showed no obvious pathological changes. The immune response induced by rwaaF was significantly higher than that of pcwaaF (p < 0.01), indicated by levels of serum concentration of IgG IL-2, IL-4, and IFN-γ, and feces concentration of sIgA. Survival rates of mice in rwaaF groups (both 80%) were also higher than in the pcwaaF groups (40 and 50%, respectively). Comparing the safety, immunogenicity, and E. coli challenge of two vaccine candidates, rwaaF had the better effect and 20 μg rwaaF was more economical. In conclusion, this study demonstrates the utility of a new E. coli vaccine and provides a rationale for further investigation of bovine mastitis therapy and management.

Progress towards the Elusive Mastitis Vaccines

Mastitis is a major problem in dairy farming. Vaccine prevention of mammary bacterial infections is of particular interest in helping to deal with this issue, all the more so as antibacterial drug inputs in dairy farms must be reduced. Unfortunately, the effectiveness of current vaccines is not satisfactory. In this review, we examine the possible reasons for the current shortcomings of mastitis vaccines. Some reasons stem from the peculiarities of the mammary gland immunobiology, others from the pathogens adapted to the mammary gland niche. Infection does not induce sterilizing protection, and recurrence is common. Efficacious vaccines will have to elicit immune mechanisms different from and more effective than those induced by infection. We propose focusing our research on a few points pertaining to either the current immune knowledge or vaccinology approaches to get out of the current deadlock. A possible solution is to focus on the contribution of cell-mediated immunity to udder protection based on the interactions of T cells with the mammary epithelium. On the vaccinology side, studies on the orientation of the immune response by adjuvants, the route of vaccine administration and the delivery systems are among the keys to success.

Invited review: A critical appraisal of mastitis vaccines for dairy cows

Infections of the mammary gland remain a frequent disease of dairy ruminants that negatively affect animal welfare, milk quality, farmer serenity, and farming profitability and cause an increase in use of antimicrobials. There is a need for efficacious vaccines to alleviate the burden of mastitis in dairy farming, but this need has not been satisfactorily fulfilled despite decades of research. A careful appraisal of past and current research on mastitis vaccines reveals the peculiarities but also the commonalities among mammary gland infections associated with the major mastitis pathogens Escherichia coli, Staphylococcus aureus, Streptococcus uberis, Streptococcus agalactiae, or Streptococcus dysgalactiae. A major pitfall is that the immune mechanisms of effective protection have not been fully identified. Until now, vaccine development has been directed toward the generation of antibodies. In this review, we drew up an inventory of the main approaches used to design vaccines that aim at the major pathogens for the mammary gland, and we critically appraised the current and tentative vaccines. In particular, we sought to relate efficacy to vaccine-induced defense mechanisms to shed light on some possible reasons for current vaccine shortcomings. Based on the lessons learned from past attempts and the recent results of current research, the design of effective vaccines may take a new turn in the years to come.

Transcriptome Profiling of m6A mRNA Modification in Bovine Mammary Epithelial Cells Treated with Escherichia coli

Mastitis is a common disease in dairy cows that is mostly caused by E. coli, and it brings massive losses to the dairy industry. N⁶-Methyladenosine (m⁶A), a methylation at the N⁶ position of RNA adenine, is a type of modification strongly associated with many diseases. However, the role of m⁶A in mastitis has not been investigated. In this study, we used MeRIP-seq to sequence the RNA of bovine mammary epithelial cells treated with inactivated E. coli for 24 h. In this in vitro infection model, there were 16,691 m⁶A peaks within 7066 mRNA transcripts in the Con group and 10,029 peaks within 4891 transcripts in the E. coli group. Compared with the Con group, 474 mRNAs were hypermethylated and 2101 mRNAs were hypomethylated in the E. coli group. Biological function analyses revealed differential m⁶A-modified genes mainly enriched in the MAPK, NF-κB, and TGF-β signaling pathways. In order to explore the relationship between m⁶A and mRNA expression, combined MeRIP-seq and mRNA-seq analyses revealed 212 genes with concomitant changes in the mRNA expression and m⁶A modification. This study is the first to present a map of RNA m⁶A modification in mastitis treated with E. coli, providing a basis for future research.