Effects of an Escherichia coli J5 vaccine on mild clinical coliform mastitis

Hit 'em Where It Hurts: Gram-Negative Bacterial Lipopolysaccharide as a Vaccine Target

Infections with antimicrobial-resistant (AMR) bacteria pose an increasing threat to the ability to perform surgical procedures, organ transplantation, and treat cancer among many other medical conditions. There are few new antimicrobials in the development pipeline. Vaccines against AMR Gram-negative bacteria may reduce the use of antimicrobials and prevent bacterial transmission. This review traces the origins of lipopolysaccharide (LPS)-based vaccines against Gram-negative bacteria, the role of O polysaccharides and LPS core regions as potential vaccine targets, the development of new vaccine technologies, and their application to vaccines in current development.

Immunization of sheep with a recombinant vaccine containing immunogenic nontoxic domains of Clostridium perfringens alpha and beta toxins

Clostridium perfringens (types A and C) can cause several diseases by secreting alpha (CPA) and beta (CPB) exotoxins in the gastrointestinal tract. Although vaccination is the main measure of immunization against C. perfringens, available vaccines have limitations in terms of productivity and safety. Thus, recombinant vaccines are an important, more effective, practical, and safer strategy in the immunization of animals. In this study, we evaluated the immunization of sheep with recombinant Escherichia coli bacterins expressing CPA and CPB complete proteins (co-administered), the immunogenic nontoxic domains rCPA-C247-370 and rCPB-C143-311 co-administered or fused as a bivalent chimera (rCPBcAc). For this, in silico analysis was performed to design rCPBcAc, considering the stability of the mRNA (-278.80 kcal/mol), the degree of antigenicity (0.7557), the epitopes of the B cell ligand, and different physicochemical characteristics. All proteins were expressed in vitro. In vivo, animals vaccinated with the co-administered antigens rCPA + rCPB and rCPA-C+ rCPB-C (200 μg each) had mean CPA and CPB neutralizing antitoxin titers of 4, 10, 4.8, and 14.4 IU/mL, respectively, while those vaccinated with 200 μg of rCPBcAc chimera (approximately 100 μg of each antigen) had titers of <4 and 12 IU/mL of CPA and CPB antitoxins, respectively, 56 days after the administration of the first dose. In addition, the chimera was considered to be immunogenic for inducing antitoxin titers using the half dose. In this study, we presented a new recombinant antigen potentially applicable for vaccines against the CPA and CPB toxins for preventing diseases caused by Clostridium perfringens.

An overview on mastitis-associated Escherichia coli: Pathogenicity, host immunity and the use of alternative therapies

Escherichia coli is one of the leading causes of bovine mastitis; it can cause sub-clinical, and clinical mastitis characterized by systemic changes, abnormal appearance of milk, and udder inflammation. E. coli pathogenicity in the bovine udder is due to the interaction between its virulence factors and the host factors; it was also linked to the presence of a new pathotype termed mammary pathogenic E. coli (MPEC). However, the presence of this pathotype is commonly debated. Its main virulence factor is the lipopolysaccharide (LPS) that is responsible for causing an endotoxic shock, and inducing a strong immune response by binding to the toll-like receptor 4 (TLR4), and stimulating the expression of chemokines (such as IL-8, and RANTES) and pro-inflammatory cytokines (such as IL-6, and IL-1β). This strong immune response could be used to develop alternative and safe approaches to control E. coli causing bovine mastitis by targeting pro-inflammatory cytokines that can damage the host tissue. The need for alternative treatments against E. coli is due to its ability to resist many conventional antibiotics, which is a huge challenge for curing ill animals. Therefore, the aim of this review was to highlight the pathogenicity of E. coli in the mammary gland, discuss the presence of the new putative pathotype, the mammary pathogenic E. coli (MPEC) pathotype, study the host's immune response, and the alternative treatments that are used against mastitis-associated E. coli.

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.

Immune response during the onset of coliform mastitis in dairy cows vaccinated with STARTVAC®

The immune response during the onset of coliform mastitis in vaccinated cows was investigated by measuring lactoferrin (LF), interleukin-8 (IL-8), and interleukin-1β (IL-1β) concentrations and somatic cell counts in 28 milk samples at the onset of acute coliform mastitis (ACM) and 73 milk samples at the onset of peracute coliform mastitis (PCM). Vaccinated ACM, unvaccinated ACM, and vaccinated PCM showed significantly higher values for LF and IL-1β levels than unvaccinated PCM (p < .01). The IL-8 concentration was lower in vaccinated PCM than in unvaccinated PCM (p < .05). There was no significant difference in somatic cell counts for each parameter. There were no significant differences in the parameters between vaccinated and unvaccinated ACM cows, or vaccinated ACM and PCM cows. From the above results, it is suggested that mastitis vaccination improved the early immune response, particularly at the onset of PCM, and played a large role in host defense against the initial infection.

A pilot study of an anti-endotoxin Ig-enriched bovine colostrum to prevent experimental sepsis

Despite the dramatic increase in antimicrobial resistance, there is a dearth of antibiotics in development and few pharmaceutical companies working in the field. Further, any new antibiotics are likely to have a short shelf life. Ab-based interventions offer alternatives that are not likely to be circumvented by the widely prevalent antibiotic resistance genes. Bovine colostrum (BC)-the first milk after parturition, rich in nutrients and immune components-promotes gut integrity and modulates the gut microbiome. We developed a hyperimmune BC (HBC) enriched in Abs to a highly conserved LOS core region of Gram-negative bacteria by immunizing pregnant cows with a vaccine comprised of detoxified LOS from Escherichia coli O111 Rc (J5) mutant non-covalently complexed to group B meningococcal outer membrane protein (J5dLOS/OMP). This vaccine generated robust levels of anti-J5 LOS Ab in the colostrum. When given orally to neutropenic rats challenged orally with Pseudomonas aeruginosa, administration of HBC improved survival compared to non-immune rats, while both BC preparations improved survival compared to PBS controls. Elevated circulating endotoxin levels correlated with mortality. HBC and to a lesser extent non-immune BC reduced bacterial burden from the liver, lung, and spleen. We conclude that HBC and to a lesser extent BC may be effective supplements that improve outcome from lethal gut-derived disseminated infection and may reduce transmission of Gram-negative bacilli from the gastrointestinal tract.

In Vitro Susceptibility of Mastitis Pathogens Isolated from Clinical Mastitis Cases on Northern German Dairy Farms

The present research study investigated the susceptibility of common mastitis pathogens—obtained from clinical mastitis cases on 58 Northern German dairy farms—to routinely used antimicrobials. The broth microdilution method was used for detecting the Minimal Inhibitory Concentration (MIC) of Streptococcus agalactiae (n = 51), Streptococcus dysgalactiae (n = 54), Streptococcus uberis (n = 50), Staphylococcus aureus (n = 85), non-aureus staphylococci (n = 88), Escherichia coli (n = 54) and Klebsiella species (n = 52). Streptococci and staphylococci were tested against cefquinome, cefoperazone, cephapirin, penicillin, oxacillin, cloxacillin, amoxicillin/clavulanic acid and cefalexin/kanamycin. Besides cefquinome and amoxicillin/clavulanic acid, Gram-negative pathogens were examined for their susceptibility to marbofloxacin and sulfamethoxazole/trimethoprim. The examined S. dysgalactiae isolates exhibited the comparatively lowest MICs. S. uberis and S. agalactiae were inhibited at higher amoxicillin/clavulanic acid and cephapirin concentration levels, whereas S. uberis isolates additionally exhibited elevated cefquinome MICs. Most Gram-positive mastitis pathogens were inhibited at higher cloxacillin than oxacillin concentrations. The MICs of Gram-negative pathogens were higher than previously reported, whereby 7.4%, 5.6% and 11.1% of E. coli isolates had MICs above the highest concentrations tested for cefquinome, marbofloxacin and sulfamethoxazole/trimethoprim, respectively. Individual isolates showed MICs at comparatively higher concentrations, leading to the hypothesis that a certain amount of mastitis pathogens on German dairy farms might be resistant to frequently used antimicrobials.

The effect of J5 bacterins on clinical, behavioral, and antibody response following an Escherichia coli intramammary challenge in dairy cows at peak lactation

Vaccination against coliform mastitis has become part of mastitis control programs in the past 3 decades, as a means of reducing the severity of clinical mastitis. Our study objective was to evaluate the effect of 2 commercially available vaccines on clinical, behavioral, and antibody response following Escherichia coli intramammary challenge in cows near peak lactation. Cows (n = 12 per group) were vaccinated with vaccine 1 (V1) or vaccine 2 (V2) at dry-off, 21 d pre-calving, and 14 d post-calving. Twelve cows served as unvaccinated controls (CTL). Cows were challenged with E. coli in a rear quarter at approximately 100 d in milk. Milk samples were collected pre- and post-challenge to enumerate E. coli and determine somatic cell count. Serum was collected before each vaccination and at d 0, 1, 2, 3, 6, 30, and 60 relative to challenge, to study antibody response. Milk IgA and tumor necrosis factor-α concentrations were determined in whey. Vaginal temperature, cow activity, and milk yield and components were monitored post-challenge. Bacterial count, somatic cell score, milk yield and component decline, vaginal temperature, activity measures, and antibody and cytokine response were analyzed for treatment differences. The effects of parity, breed, and a repeated measure of time were also tested. Seven cows had to be removed from the study post-challenge for antibiotic treatment (CTL and V1, n = 3 each; V2, n = 1), 2 of which were euthanized (both CTL). Vaccinated cows exhibited fever (vaginal temperature ≥39.4°C) 3 h earlier than CTL cows, but we found no differences between treatments for bacterial count, somatic cell score, or milk yield reduction. Vaccinated cows spent more time lying per rest bout 2 d post-challenge, but total daily lying time was not different from CTL cows during the 7 d post-challenge. The vaccines differed in antibody response: V1 cows had greater serum IgG₁ and IgG₂ post-challenge. A parity effect was also evident: primiparous cows had lower bacterial counts, somatic cell score and a smaller milk yield decline than multiparous cows, but also had lower antibody production. Immunization with either J5 bacterin did not reduce clinical signs of mastitis in cows challenged at 100 d in milk, demonstrating that the effects of J5 vaccination had diminished at peak lactation.

Symposium review: Intramammary infections-Major pathogens and strain-associated complexity

Intramammary infection (IMI) is one of the most costly diseases to the dairy industry. It is primarily due to bacterial infection and the major intramammary pathogens include Escherichia coli, Streptococcus uberis, and Staphylococcus aureus. The severity and outcome of IMI is dependent on several host factors including innate host resistance, energy balance, immune status, parity, and stage of lactation. Additionally, the infecting organism can influence the host immune response and progression of disease. It is increasingly recognized that not only the infecting pathogen species, but also the strain, can affect the transmission, severity, and outcome of IMI. For each of 3 major IMI-associated pathogens, S. aureus, Strep. uberis, and E. coli, specific strains have been identified that are adapted to the intramammary environment. Strain-dependent variation in the host immune response to infection has also been reported. The diversity of strains associated with IMI must be considered if vaccines effective against the full repertoire of mammary pathogenic strains are to be developed. Although important advances have been made recently in understanding the molecular mechanism underpinning strain-specific virulence, further research is required to fully elucidate the cellular and molecular pathogenesis of mammary adapted strains and the role of the strain in influencing the pathophysiology of infection. Improved understanding of molecular pathogenesis of strains associated with bovine IMI will contribute to the development of new control strategies, therapies, and vaccines. The development of enabling technologies such as pathogenomics, transcriptomics, and proteomics can facilitate system-level studies of strain-specific molecular pathogenesis and the identification of key mediators of host-pathogen interactions.

A 100-Year Review: Mastitis detection, management, and prevention

Mastitis is the most frequent disease of dairy cows and has well-recognized detrimental effects on animal wellbeing and dairy farm profitability. Since the beginning of modern dairy farming, producers have sought effective methods to minimize the occurrence of mastitis in their herds. The objective of this paper is to review and highlight important advances in detection, management, and prevention of mastitis that have occurred since the first volume of the Journal of Dairy Science was published in 1917. Initial research efforts were directed at understanding the nature of pathogenic bacteria that were responsible for most intramammary infections. For decades, researchers worked to identify effective strategies to control mastitis caused by Streptococcus agalactiae and Staphylococcus aureus. To develop successful control programs, mastitis workers first had to identify mechanisms of infection, define the clinical and subclinical states of the disease, discover appropriate screening tests, determine likely points of exposure, identify pathogen-specific characteristics, and develop effective procedures for machine milking. Pioneering researchers eventually recognized that mastitis control was based on preventing new infections from occurring in healthy cows and reducing the duration that cows remained infected. Development of a control program that incorporated post-milking teat dipping, hygienic milking procedures, and strategic use of antibiotic therapy at dry-off resulted in widespread control of contagious pathogens. As herd management changed, researchers were tasked with defining control of mastitis caused by opportunistic pathogens originating from environmental sources. As mastitis pathogens have evolved, researchers have sought to define antimicrobial usage that will maintain animal wellbeing while minimizing unnecessary usage. During the last century, tremendous significant advances in mastitis control have been made but changing herd structure and more rigorous processor standards ensure that mastitis will remain an important subject focus of future research.

The Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) identification versus biochemical tests: a study with enterobacteria from a dairy cattle environment

Mastitis adversely affects milk production and in general cows do not regain their full production levels post recovery, leading to considerable economic losses. Moreover the percentage decrease in milk production depends on the specific pathogen that caused the infection and enterobacteria are responsible for this greater reduction. Phenotypic tests are among the currently available methods used worldwide to identify enterobacteria; however they tend to misdiagnose the species despite the multiple tests carried out. On the other hand The Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS) technique has been attracting attention for its precise identification of several microorganisms at species level. In the current study, 183 enterobacteria were detected in milk (n = 47) and fecal samples (n = 94) from cows, and samples from water (n = 23) and milk lines (n = 19). All these samples were collected from a farm in Rio de Janeiro with the specific purpose of presenting the MALDI–TOF MS technique as an efficient methodology to identify Enterobacteriaceae from bovine environments. The MALDI–TOF MS technique results matched the biochemical test results in 92.9% (170/183) of the enterobacteria species and the gyrB sequencing confirmed 100% of the proteomic technique results. The amino acid decarboxylation test made the most misidentifications and Enterobacter spp. was the most misidentified genus (76.9%, 10/13). These results aim to clarify the current biochemical errors in enterobacteria identification, considering isolates from a bovine environment, and show the importance for more careful readings of phenotypic tests which are often used in veterinary microbiology laboratories.

Intramammary immunization with ultraviolet-killed Escherichia coli shows partial protection against late gestation intramammary challenge with a homologous strain

The objective of this study was to evaluate the efficacy of intramammary immunization with UV-killed Escherichia coli ECC-Z on prevention of intramammary colonization after a challenge with a dose of the homologous E. coli ECC-Z live bacteria. A total of 10 cows were included in a study to evaluate the efficacy of intramammary immunization. All 10 cows received an intramammary immunization of 100 cfu of UV-killed E. coli ECC-Z bacteria into one hind quarter at the time of dry off. Approximately 2wk before the anticipated calving date, both hind quarters of all cows were challenged with 100 cfu of live E. coli ECC-Z bacteria. Five of the cows were vaccinated parenterally with a commercial J5 bacterin, and 5 cows served as controls with no parenteral vaccination. The cows were then followed over time and infection risk, clinical scores, somatic cell count, and milk production were observed over time. The results of these 10 cows showed partial protection of intramammary immunization on the outcome of a subsequent homologous intramammary challenge. Immunization resulted in a lower probability of infection, a lower bacteria count, lower somatic cell counts and milk conductivity, a lower clinical mastitis score, and increased milk production compared with unimmunized control quarters. Once the analysis was corrected for immunization, parenteral J5 vaccination had no significant effect on any of the measured parameters. These results provide the first evidence that intramammary immunization may improve the outcome of an intramammary E. coli infection in late gestation and onset of mastitis immediately following parturition. Unlike systemic vaccination, which generally does not reduce the intramammary infection risk, the intramammary immunization did show a 5-times reduced odds of an established intramammary infection after challenge. Cytokine profiles indicated a local return of proinflammatory response after challenge as the data showed a more pronounced increase in in IFN-γ with a subsequent negative feedback due to a spike in the level of IL-10 in immunized quarters relative to nonimmunized quarters. Although these results are preliminary and obtained on only 10 cows, the results provide insight into the biological benefits of triggering mucosal immunity in the mammary gland.

Activity and milk compositional changes following experimentally induced Streptococcus uberis bovine mastitis

Milk constituents and physical activity of cows experimentally infected with Streptococcus uberis mastitis were compared with those of uninfected cows. Twelve late-lactation Holsteins cows were paired based on milk production and parity. One cow in each pair was experimentally infected in the right front mammary gland with Strep. uberis. The remaining cow in each pair served as an uninfected control. Real-time analyses of milk constituents provided fat, protein, and lactose percentages at each milking. Pedometers were placed on the left front leg of all cows and activity was measured. Intramammary infections with Strep. uberis reduced milk yield in experimental cows by approximately 1.6kg/d in the first week after challenge compared with control cows. Lactose percentage in milk was reduced on d 3, 4, 5, and 6 after challenge in treatment cows compared with controls. Percentages of fat and protein in milk did not differ between infected and uninfected cows the week after infections were induced. Total steps per day were reduced and minutes resting per day were increased the week after experimental challenge in infected cows compared with control cows. The number of resting bouts did not differ between infected and uninfected cows. Changes in percentage of lactose in milk and animal activity caused by experimentally induced Strep. uberis mastitis were detected by the automated milk analyzer and pedometer systems.

Vacinação com Escherichia coli J5 no pré-parto e ocorrência de mastite e produção de leite de vacas mestiças leiteiras

Avaliaram-se a utilização da vacina Escherichia coli J5 no período pré-parto e a ocorrência de mastite e de produção de leite. Foram utilizadas 93 vacas, sendo 43 vacinadas e 50 não vacinadas. Para a análise dos dados de produção e CCS (contagem de células somáticas), utilizou-se delineamento inteiramente ao acaso em sistemas de parcelas subdivididas. Os dados de CCS e duração de casos clínicos de mastite foram transformados em Log10CCS. Para as médias de CCS e a duração de casos clínicos, usou-se o teste t. Para comparações de médias de recidivas de casos clínicos, usou-se o teste de Mann-Whitney. Para frequência de microrganismos e de mastite subclínica, usou-se o teste de qui-quadrado. A interação dessas variáveis foi analisada pelo teste de McNemar. Não houve redução na prevalência de infecções por coliformes entre a secagem e o parto nos dois grupos. A duração total dos casos clínicos de mastite em animais que apresentaram mastite clínica foi menor em vacas vacinadas. O número de episódios clínicos e a intensidade dos casos clínicos não diferiu entre os grupos. A prevalência de animais com mastite subclínica no pós-parto e a (CCS) nos 100 primeiros dias de lactação foram mais baixas no grupo de animais vacinados. Não foi observada diferença na produção de leite entre os grupos. A vacinação de vacas com E. coli J5 melhora a saúde da glândula mamária de vacas leiteiras e, consequentemente, reduz a prevalência de animais com mastite subclínica no pós-parto, bem como a duração dos casos clínicos de mastite e a CCS nos 100 primeiros dias de lactação.

Lipopolysaccharide priming enhances expression of effectors of immune defence while decreasing expression of pro-inflammatory cytokines in mammary epithelia cells from cows

Background

Udder infections with environmental pathogens like Escherichia coli are a serious problem for the dairy industry. Reduction of incidence and severity of mastitis is desirable and mild priming of the immune system either through vaccination or with low doses of immune stimulants such as lipopolysaccharide LPS was previously found to dampen detrimental effects of a subsequent infection. Monocytes/macrophages are known to develop tolerance towards the endotoxin LPS (endotoxin tolerance, ET) as adaptation strategy to prevent exuberant inflammation.

We have recently observed that infusion of 1 μg of LPS into the quarter of an udder effectively protected for several days against an experimentally elicited mastitis. We have modelled this process in primary cultures of mammary epithelial cells (MEC) from the cow. MEC are by far the most abundant cells in the healthy udder coming into contact with invading pathogens and little is known about their role in establishing ET.

Results

We primed primary MEC cultures for 12 h with LPS (100 ng/ml) and stimulated three cultures either 12 h or 42 h later with 10⁷/ml particles of heat inactivated E. coli bacteria for six hours. Priming-related alterations in the global transcriptome of those cells were quantified with Affymetrix microarrays. LPS priming alone caused differential expression of 40 genes and mediated significantly different response to a subsequent E. coli challenge of 226 genes. Expression of 38 genes was enhanced while that of 188 was decreased. Higher expressed were anti-microbial factors (β-defensin LAP, SLPI), cell and tissue protecting factors (DAF, MUC1, TGM1, TGM3) as well as mediators of the sentinel function of MEC (CCL5, CXCL8). Dampened was the expression of potentially harmful pro-inflammatory master cytokines (IL1B, IL6, TNF-α) and immune effectors (NOS2, matrix metalloproteases). Functional network analysis highlighted the reduced expression of IL1B and of IRF7 as key to this modulation.

Conclusion

LPS-primed MEC are fitter to repel pathogens and better protected against misguided attacks of the immune response. Attenuated is the exuberant expression of factors potentially promoting immunopathological processes. MEC therefore recapitulate many aspects of ET known so far from professional immune cells.

Perspectives on immunoglobulins in colostrum and milk

Immunoglobulins form an important component of the immunological activity found in milk and colostrum. They are central to the immunological link that occurs when the mother transfers passive immunity to the offspring. The mechanism of transfer varies among mammalian species. Cattle provide a readily available immune rich colostrum and milk in large quantities, making those secretions important potential sources of immune products that may benefit humans. Immune milk is a term used to describe a range of products of the bovine mammary gland that have been tested against several human diseases. The use of colostrum or milk as a source of immunoglobulins, whether intended for the neonate of the species producing the secretion or for a different species, can be viewed in the context of the types of immunoglobulins in the secretion, the mechanisms by which the immunoglobulins are secreted, and the mechanisms by which the neonate or adult consuming the milk then gains immunological benefit. The stability of immunoglobulins as they undergo processing in the milk, or undergo digestion in the intestine, is an additional consideration for evaluating the value of milk immunoglobulins. This review summarizes the fundamental knowledge of immunoglobulins found in colostrum, milk, and immune milk.

Characterization of specific egg yolk immunoglobulin (IgY) against mastitis-causing Staphylococcus aureus

AIMS

To evaluate the in vitro activity of egg yolk immunoglobulin (IgY) against mastitis-causing Staphylococcus aureus.

METHODS AND RESULTS

Specific IgY was produced by immunizing hens with formaldehyde-killed Staph. aureus, using a bacterial strain known to cause mastitis. The IgY, of 94% purity, was obtained from yolks by water dilution, salt precipitations, ultrafiltration and gel filtration. ELISA indicated that the IgY produced was specific to the antigen and five Staph. aureus isolates obtained from mastitic cows. The growth of Staph. aureus was inhibited by specific IgY at concentrations from 1 to 10 mg ml(-1) in a dose-dependent manner. The phagocytosis of Staph. aureus by milk macrophages was enhanced in the presence of specific IgY with the highest phagocytic percentage being 30% higher than that without IgY (P < 0.05).

CONCLUSIONS

The specific IgY against mastitis-causing Staph. aureus inhibited the growth of Staph. aureus and enhanced the phagocytosis of Staph. aureus by milk macrophages.

SIGNIFICANCE AND IMPACT OF THE STUDY

Specific IgY would be a potential treatment for bovine mastitis.

Nutrition and udder health in dairy cows: a review

Mastitis is still one of the three main diseases that affects the profitability of dairy farmers. Despite the implementation of the five-point mastitis control programme in the early 1970 s, the incidence in the UK has not reduced dramatically over the past 10 years. A review of the scientific literature indicates that there is a link between nutrition and mastitis in the dairy cow. The major impact of nutrition on udder health is via suppression of the immune system. Cows in negative energy balance are at a higher risk of ketosis and clinical ketosis is associated with a two-fold increase in the risk of clinical mastitis. Trace minerals and vitamins that can affect udder health are selenium and vitamin E, copper, zinc, and vitamin A and β-carotene.

Molecular subtyping of mastitis-associated Klebsiella pneumoniae isolates shows high levels of diversity within and between dairy herds

Despite advances in controlling mastitis (inflammation of the mammary gland), udder infections caused by Klebsiella pneumoniae continue to affect dairy cattle. Mastitis caused by K. pneumoniae responds poorly to antibiotic treatment, and as a consequence, infections tend to be severe and long lasting. We sought to determine whether a nonrandom distribution of specific genotypes of K. pneumoniae was associated with mastitis from 6 dairy herds located in 4 different states. A total of 635 isolates were obtained and fingerprinted by repetitive DNA sequence PCR. Significant genetic diversity was observed in 4 of the 6 dairy herds analyzed, and a total of 49 genotypic variants were identified. Within a herd, Simpson's diversity indices were 91.0, 94.1, 91.7, 88.6, 53.3, and 64.3% for dairies A, B, C, D, E, and F, respectively. The association between matrices of genetic similarity and matrices of temporal distance was negative in all the dairies analyzed. Four dairies had a high incidence of K. pneumoniae mastitis during the winter. The majority of genotypes were unique to herds of origin, and only 5 genotypes were detected in more than 2 dairies. Genotype 1 (arbitrary designation) occurred most frequently across dairies and was found in 25.2% of all mastitis cases and among 22.8% of reinfected and culled cows in dairy A. Specific genotypes also tended to be associated with a specific bedding type and dairy location. Analysis of molecular variance showed that 18% of the genetic diversity was due to variation among herds within states, and 82% of the genetic diversity was accounted for by variation of genotypes within herds. The data support the idea that mastitis is caused by a diverse group of K. pneumoniae genotypes and thus has major implications for the diagnosis, prevention, and treatment of udder infections in dairy cows.

The toll-like receptor-4 (TLR-4) pathway and its possible role in the pathogenesis of Escherichia coli mastitis in dairy cattle

Mastitis is one of the most costly production diseases in the dairy industry that is caused by a wide array of microorganisms. In this review, we focus on the Gram-negative Escherichia coli infections that often occur at periods when the innate immune defence mechanisms are impaired (i.e., parturition through the first 60 days of lactation). There is substantial evidence demonstrating that at these periods, the expected influx of polymorphonuclear neutrophil leukocytes (PMN) into the mammary gland is delayed during inflammation after intramammary infection with E. coli. Here, we provide some hypotheses on the potential mechanisms of action on how the disease may develop under circumstances of immunosuppression, and describe the potential involvement of the toll-like receptor-4 signal transduction pathway in the pathogenesis of E. coli mastitis. In addition, some ideas are proposed to help prevent E. coli mastitis and potentially other diseases caused by Gram-negative infections in general.

In Vitro Growth of Enterococci of Bovine Origin in Bovine Mammary Secretions from Various Stages of Lactation

In vitro growth responses of Enterococcus faecium and Enterococcus faecalis were tested in cell-free, fat-free bovine mammary secretions. Mammary secretions were collected during the dry period, and during early, late, and extended lactation. Sixty-three enterococcal isolates from aseptically collected bovine quarter milk samples and bedding samples from a commercial dairy herd were tested. Isolates from bovine quarter milk samples originated from mammary glands with clinical mastitis, cows with composite somatic cell score >4, postpartum milk samples, or from routine milk samples submitted to a mastitis diagnostic laboratory. Source of enterococcal isolates and the species significantly contribute to the ability of organisms to multiply in mammary secretions from various stages of lactation. Isolates collected from milk samples of the commercial herd and isolates from milk submitted to a mastitis diagnostic lab did not display enhanced growth in mammary secretions compared with isolates from bedding. Growth responses of E. faecalis were greater than those for E. faecium in secretions collected during the dry period, late lactation, and extended lactation. Bacterial growth did not differ between enterococcal species in mammary secretion collected from cows in early lactation. Differences in bacterial growth between E. faecalis and E. faecium in mammary secretions may indicate differences between species in susceptibility of mammary glands during the lactation cycle.

Relationship between antimicrobial susceptibility of clinical mastitis pathogens and treatment outcome in cows

OBJECTIVE

To determine whether there was any association between results of in vitro antimicrobial susceptibility testing of pathogens isolated from cows with mild or moderate clinical mastitis and outcome of treatment.

DESIGN

Observational study.

ANIMALS

133 cows with mild or moderate mastitis in a single quarter.

PROCEDURE

Cows were treated by means of intramammary infusion of pirlimycin (50 mg) in the affected quarter once daily for 2 days; additional intramammary treatments with the same product were administered if the milk continued to appear abnormal. Duration of treatment and days until clinical cure were recorded. Bacterial isolates were tested for antimicrobial susceptibility by means of a broth micro-dilution technique.

RESULTS

Environmental streptococci, coliforms, and coagulase-negative Staphylococcus spp were the most commonly isolated pathogens. Duration of treatment and days until clinical cure were not significantly different for cows from which pathogens that were susceptible or resistant to pirlimycin were isolated. Bacteriologic cure rates 14 and 21 days after treatment were not significantly different for cows with mastitis caused by susceptible or resistant bacteria. Similar results were found when data only from cows with mastitis caused by gram-positive isolates were analyzed.

CONCLUSIONS AND CLINICAL RELEVANCE

In the present study, differences in clinical outcome for cows with mild or moderate mastitis that could be attributed to differences in results of in vitro susceptibility testing were not identified. The use of in vitro susceptibility testing to guide intramammary mastitis treatment cannot be recommended on the basis of results of this study.

Effects of adjuvants on safety and efficacy of an Escherichia coli J5 bacterin

The effects of using a water-soluble adjuvant or an emulsified oil-based adjuvant on the safety, antibody titer, and clinical responses of an Escherichia coli J5 bacterin were tested in an experimental infection trial. Fifty-one cows were assigned to 17 blocks of 3. Two cows within each block of 3 were vaccinated with a commercially prepared E. coli J5 bacterin containing either a water-soluble adjuvant or the same bacterin preparation emulsified in oil. One cow in each block was an unvaccinated control. Cows were immunized at drying off and 42 d later. The right or left front mammary quarter of each experimental cow was challenged by intramammary infusion of E. coli 727 between 14 and 35 DIM. Areas of inflammation at the primary injection site were greater 1, 2, and 3 d following primary vaccination for bacterin containing oil-in-water adjuvant compared with bacterin containing water-soluble adjuvant. Whey anti-E. coli J5 IgG titers were higher at calving for cows vaccinated with bacterin containing oil-in-water adjuvant than for cows either vaccinated with bacterin containing water-soluble adjuvant or unvaccinated controls. Serum x-E. coli J5 IgG titers were higher at calving for vaccinated cows than for unvaccinated controls. Peak bacterial counts in milk from challenged quarters were greater for unvaccinated controls than for cows vaccinated with bacterin containing water-in-oil adjuvant. Bacterial counts in milk from challenged quarters and clinical score both were greater in unvaccinated controls than cows vaccinated with bacterin containing water-in-oil adjuvant between 12 and 24 h postchallenge. Clinical responses were similar between unvaccinated controls and cows vaccinated with bacterin containing water-soluble adjuvant.

Moderate Inflammatory Reaction During Experimental Escherichia coli Mastitis in Primiparous Cows

Nineteen primiparous cows were experimentally infected in 2 quarters with 1 x 10(4) (group A) or 1 x 10(6) (group B) cfu of Escherichia coli P4:O32 per quarter within 2 to 4 wk after parturition. Blood and milk samples were collected from all primiparous cows at regular time intervals from d -4 to d +3 relative to inoculation. Milk production rapidly decreased in both groups during E. coli mastitis, but recovery appeared to be faster in group B at d + 1 postinfusion (p.i.). The milk production losses in the noninfected quarters were substantial on the day of inoculation, which is probably due to pronounced systemic effects. However, on d + 2 p.i. milk production in the noninfected quarters nearly reached preinfection levels, indicating a moderate clinical severity following intramammary inoculation. None of the other severity criteria evolved towards a severe response pattern. Reticulorumen motility was inhibited in both groups during E. coli mastitis. The clinical episode was short lasting in both groups. Rectal temperature, heart rate, blood leukocyte count, number of colony-forming units, milk somatic cell count and several indicators for the disintegration of the blood-milk barrier returned to normal values within 24 to 72 h p.i. Primiparous cows reacted with a moderate inflammatory response following intramammary infusion with a relatively high dose of E. coli. Despite the use of a high inoculum dose, primiparous cows in both groups showed pronounced resistance against severe intramammary E. coli infection. A possible effect of the inoculum dose could be present, however, further research into the effect of the inoculum dose on the inflammatory response should be performed.

Changes in Vitamin C Concentrations in Plasma and Milk from Dairy Cows After an Intramammary Infusion of Escherichia coli

Plasma and milk concentrations of ascorbic acid and dehydro-L-ascorbic acid (DHAA) were measured before and after 21 Holstein cows (approximately 26 DIM) were given an intramammary infusion of Escherichia coli. Blood, milk from the unchallenged quarters, and milk from the challenged gland were sampled immediately before challenge (d 0) and 24 h and 7 d postchallenge. Plasma vitamin C (ascorbic acid + DHAA) concentrations decreased 39%, and concentrations of vitamin C and ascorbic acid in milk from the challenged quarter decreased 52 and 62%, respectively, in samples taken 24 h postchallenge. No change was observed in vitamin C concentrations in milk from unchallenged quarters. The concentration of DHAA in milk from challenged quarters increased 67% 24 h postchallenge. The duration of clinical mastitis, peak body temperature, number of colony-forming units of E. coli isolated from the infected gland, and loss in milk yield were associated with a change in concentration of vitamin C in milk from the challenged quarter. Increased severity of clinical signs was associated with large decreases in concentration of vitamin C in milk from the challenged quarter. Similar, but statistically weaker, relationships were observed for changes in plasma vitamin C concentrations.

Role of dietary copper in enhancing resistance to Escherichia coli mastitis

The role of dietary copper in enhancing resistance to Escherichia coli mastitis was investigated in first-lactation heifers. Twenty-three primigravid Holstein heifers were maintained on a basal (6.5 ppm copper; -Cu) diet or a diet supplemented (20 ppm) with copper sulfate (+Cu) beginning 60 d prepartum through 42 d of lactation. Liver biopsies and blood samples were taken for liver and blood minerals and plasma ceruloplasmin. Milk samples were taken weekly postpartum for bacteriology. The overall mean liver Cu concentration was about threefold higher, and the overall mean plasma Cu concentration was greater in the +Cu group than the -Cu group. At 34 d of lactation, one pathogen-free quarter per animal was infused with 22 cfu of Escherichia coli strain 727. Plasma Cu was greater at -24, 0, 18, 24, 36, 96, 192, and 240 h relative to infusion for +Cu animals. Plasma Zn concentration was higher at 24 h for the +Cu group. Milk bacterial count (log10 cfu/ml) was lower at 12, 18, and 48 h for the +Cu group. Somatic cell count (log10/ml) was lower at 18 h in +Cu animals. Clinical score at 24 h was lower for +Cu cows, while at 144 h, clinical score was lower for -Cu cows. Rectal temperature was lower at 18 h for the +Cu group. Plasma ceruloplasmin and Fe, dry matter intake and milk production did not differ. Copper supplementation reduced the clinical response during experimental E. coli mastitis, but duration was unchanged.

Rumen fermentation and nitrogen balance of lambs fed diets containing plant extracts rich in tannins and saponins, and associated emissions of nitrogen and methane

Tannins were added to experimental diets at levels of 1 and 2 g/kg DM (hydrolysable tannins; Castanea sativa wood extract) and saponins at 2 and 30 mg/kg DM (sarsaponin; Yucca schidigera extract). These levels were far below thresholds expected to be adverse in ruminants. Effects were measured in lambs by comparison with unsupplemented control diets calculated to be either deficient (10%) or adequate in protein. The diets consisted of hay, concentrate (1:1) and extra wheat starch with increasing body weight. Ruminal pH, VFA concentration, protozoa count and apparent digestibilities of organic matter and fibre did not differ among treatments. The low tannin dose significantly decreased bacteria count compared to the high saponin dose. Saponin supplementation and the high tannin dose showed some potential to reduce ruminal ammonia concentration. This was associated with weak trends towards lower urine N excretion (only tannins) and ammonia emission from manure. Methane release was increased by the low tannin dose compared to the unsupplemented control. Diet effects on heat production were not systematic. In conclusion, the extracts rich in tannins or saponins gave only slight indications for either increased body nitrogen retention or reduced nitrogen emission. However, effects might have been larger with more pronounced dietary protein deficit.

Vaccines and diagnostic methods for bovine mastitis: fact and fiction

A number of problems are uniquely associated with vaccination of dairy cows for mastitis. One of these is that the number of mastitis pathogens is numerous and heterogeneous. Vaccine efforts have concentrated mainly on the major mastitis pathogens. While at least one S. aureus bacterin has been commercially available for a number of years, no large-scale, independent field trials have been published in refereed journals which support the efficacy of this vaccine. Experimental vaccines for S. aureus composed of pseudocapsule-enriched bacterins supplemented with alpha- and/or beta-toxoids appear promising, but none of these has been commercialized. With S. uberis, some protection against homologous strain challenges was reported recently with a live strain and a bacterin, but other data from the same laboratory showed this vaccine would not protect against heterologous challenge strains. At this time there is only one highly effective vaccine for mastitis, the core-antigen vaccine for coliform mastitis. All of the commercially available vaccines for this indication are bacterins of rough mutants of E. coli strain J5 or Salmonella spp. Preliminary success with an experimental vaccine based on the plasminogen activator of S. uberis is a very different approach for a mastitis vaccine. Little success has been reported with vaccination against other mastitis pathogens. For diagnostic methods, the high somatic cell count, as measured by direct count or indirect assays, remains the cornerstone of mastitis diagnosis. However, for subclinical mastitis, bacterial cell culture is a reliable diagnostic method. Pathogen identification may rely on older biochemical testing methods or newer commercial identification systems, depending on the laboratory budget. ELISA assays also have been used to assess herd infection status. Epidemiologic studies have used DNA fingerprinting and ribotyping, but none of these methods has yet produced an easily utilized commercial format. Within the next decade, additional efficacious vaccines for several of the most common agents for bovine mastitis are likely. A review written at that time then can be more fact than fiction.

Use of systemic disease signs to assess disease severity in dairy cows with acute coliform mastitis

OBJECTIVE

To evaluate the use of systemic disease signs for classifying severity of acute coliform mastitis in dairy cows.

DESIGN

Prospective cohort study.

ANIMALS

144 dairy cows.

PROCEDURE

Cows were examined at the time of initial identification of disease (time 0) and classified as having mild, moderate, or severe disease on the basis of rectal temperature, hydration status, rumen contraction rate, and attitude. A CBC and serum biochemical analyses were performed, and milk samples were submitted for bacterial culture at time 0 and 48 hours later.

RESULTS

69 cows were classified as having mild disease, 44 as having moderate disease, and 31 as having severe disease. Median WBC and neutrophil counts were significantly lower in cows with moderate or severe disease at time 0 than in cows with mild disease. Band neutrophil count was significantly higher at 48 hours and serum calcium concentration was significantly lower at time 0 and at 48 hours in cows with severe or moderate disease, compared with cows with mild disease. Twenty-eight, 51, and 77% of cows with mild, moderate, and severe disease, respectively, had > 100,000 colony-forming units/ml of milk at time 0. The odds that a cow with severe disease would die or be culled were 3.6 times the odds for a cow with moderate disease and 11.2 times the odds for a cow with mild disease.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that a classification scheme based on readily observable systemic disease signs can be used to classify disease severity in cows with acute coliform mastitis.

A comparison of two commercially available Escherichia coli J5 vaccines against E. coli intramammary challenge

The efficacy of two commercially available Escherichia coli J5 bacterins was investigated. Jersey cows were randomly assigned to one of three treatment groups: 1) unvaccinated controls, 2) vaccinated with J.VAC (Merial Limited, Athens, GA), and 3) vaccinated with J5 bacterin. All cows were vaccinated at drying off and at 2 wk before anticipated calving. Cows that were vaccinated with the J5 bacterin also received a third immunization at calving. One quarter of each cow was challenged with approximately 64 cfu of E. coli at 14 to 30 d postcalving. Immunization by either vaccine did not influence the severity of coliform mastitis; however, the mean number of colony-forming units of E. coli recovered from challenged quarters was significantly lower for immunized cows than for control cows at 144 h postchallenge. Serum and mammary secretion immunoglobulin (Ig)G, IgG1, and IgG2 titers against E. coli J5 whole-cell antigens were enhanced in vaccinated cows. Serum and mammary secretion IgM were not different among treatment groups. Somatic cell counts in milk from challenged quarters, rectal temperatures, and the clinical status of cows following intramammary challenge were not different among treatment groups.

Efficacy of intramammary immunization with an Escherichia coli J5 bacterin

Intramammary immunization was investigated as a procedure to reduce the clinical signs of coliform mastitis. Twenty-four cows were equally distributed to the following Escherichia coli J5 immunization schedules: 1) Subcutaneous injection 14 d prior to the end of lactation, intramammary immunization 7 d after drying off, and subcutaneous injection 30 d into the dry period; 2) subcutaneous injections at drying off, at 30 d into the dry period, and within 12 h after calving; and 3) unimmunized controls. Intramammary immunizations were the infusion of vaccine via the teat canal into each of the four mammary glands. Cows were challenged by infusion of E. coli 727 into one uninfected mammary quarter at approximately 30 d after calving. Intramammary immunization enhanced antibody titers against E. coli J5 and E. coli 727 compared with subcutaneous immunization. Immunoglobulin G titers against E. coli J5 and E. coli 727 in whey were greater at the time of challenge and 7 d after challenge for cows that received the intramammary immunization than for cows immunized by only subcutaneous injections. Serum IgG titers against E. coli 727 were enhanced at 7 d after challenge for cows receiving intramammary immunizations compared with conventionally immunized cows. Serum IgM titers against E. coli 727 were higher at calving for cows receiving intramammary immunization compared with conventionally immunized cows. Immunization schedule had minimal effect on systemic and local signs of clinical mastitis following challenge.

Efficacy of an Escherichia coli J5 bacterin administered to primigravid heifers

The efficacy of an Escherichia coli J5 bacterin for reducing the incidence of intramammary infections and clinical signs of mastitis was tested in first lactation heifers. Ten primigravid heifers were immunized with an E. coli J5 bacterin. Four heifers received a placebo. The bacterin and placebo were injected subcutaneously approximately 60 d prior to calving, 28 d later, and within 48 h after calving. Vaccinated and placebo-injected heifers were challenged by intramammary infusion of E. coli 727 in one mammary gland between 23 and 37 d after calving. All challenged quarters were diagnosed with an intramammary infection within 6 h after bacteria were infused. The severity and duration of local signs of clinical mastitis were reduced in vaccinated heifers compared with placebo-injected heifers. Systemic signs of clinical mastitis were limited and did not differ between treatment groups. Bacteria counts in milk from challenged quarters were lower in vaccinated heifers than in control heifers at 12, 15, and 48 h after challenge. Serum immunoglobulin G titers against whole-cell E. coli J5 antigen at calving were higher in vaccinated heifers than they were in controls. Vaccinated heifers had higher immunoglobulin G titers than did controls in mammary secretions at calving and immediately prior to challenge. Immunization of primigravid heifers with an E. coli J5 bacterin during the last trimester of gestation and at calving reduced the severity and duration of clinical signs following intramammary challenge with a heterologous strain of E. coli.

Approaches to modeling intramammary infections in dairy cattle

In this paper, three approaches (Markov processes, discrete-event simulation, and differential equations) to modeling intramammary infections (IMI; focusing on the dynamic changes between uninfected, subclinical, and clinical udder health states) are described. The objectives were to describe the various approaches to modeling intramammary infections, determine if simulations of the examples of the three approaches yield stable prevalences, and discuss the approaches' limitations. The literature review showed that there is no agreement on the proportion of animals that change health states. The approach of discrete-event simulation modeling included the most cow-level risk factors and udder-health states (hence, was judged to replicated best the dynamics of the infection process) and yielded stable prevalences for all udder-health states. However, there remain parts of the dynamics that need further research. These include the pathogen-specific probabilities and times of occurrence for: regression of clinical IMI to subclinical IMI, flare-up of subclinical IMI to clinical IMI, and incidence of subclinical IMI. Also, the assumption in all current approaches of homogeneous mixing is violated because the primary contact structure for contagious pathogens during milking is either between cows through residual infectious milk in the milking machine or within a cow by vacuum fluctuations or teat-cup liner slips. Better contact structures should be incorporated so that the effects of control strategies can be better-estimated. Moreover, the three modeling approaches discussed assumed that all non-infected quarters are susceptible to infection--which might be denied by work in genetic resistance.

Influence of route of vaccine administration against experimental intramammary infection caused by Escherichia coli

The route of immunization of a commercially available Escherichia coli J5 bacterin was investigated. Jersey cows were randomly assigned to one of three treatment groups: 1) unvaccinated (control), 2) vaccinated subcutaneously in the neck, and 3) vaccinated in the area of the supramammary lymph node. Cows were vaccinated at drying off and at 2 wk prior to anticipated calving. Two quarters of each cow were challenged with approximately 60 cfu of E. coli at 14 d postcalving. Route of immunization in the neck or the area of the supramammary lymph node did not influence severity of coliform mastitis. However, the mean number of colony-forming units of E. coli recovered from challenged quarters was significantly lower for vaccinated cows than for control cows at 24 h postchallenge. A quicker milk yield recovery following intramammary challenge was also observed for vaccinated cows. Serum immunoglobulin (Ig) G, IgG1, and IgG2 and whey IgG1 and IgG2 antibody titers against E. coli J5 whole-cell antigens were significantly enhanced in vaccinated cows. Somatic cell counts in milk from challenged quarters and rectal temperatures following intramammary challenge were not different for cows across treatment groups. Immunization did not prevent intramammary infection.

Effects of a core antigen vaccine against gram-negative bacteria on physiologic and yield parameters of dairy cows during late lactation and the dry period

The objective of the study was to assess the effects of a core antigen vaccine against Gram-negative bacteria on feed consumption, milk yield, somatic cell count, hematologic parameters, and milk progesterone concentrations for dairy cows in late lactation and the dry period. Sixty-eight multiparous Holstein cows from two farms were paired by days in milk and were randomly selected to receive either the vaccine or placebo. Cows received a secondary immunization with the same product (vaccine or placebo) 3 wk following the primary immunization. The physiologic and yield outcomes were measured prior to each immunization, at the time of each immunization, and for one or more periods following each immunization. No significant differences between vaccinated and placebo groups were detected for daily milk weight, daily feed intake, somatic cell score, rectal body temperature, or milk progesterone concentration (pregnant cows). Cows in the vaccinated group had significant elevations in total blood leukocyte counts following the secondary immunization, which was due to an increase in the neutrophil fraction 24 h postimmunization.

alpha-Tocopherol concentrations in milk and plasma during clinical Escherichia coli mastitis

Eighteen cows were challenged by intramammary infusion with Escherichia coli 727 to determine the effects of acute clinical mastitis on alpha-tocopherol concentrations in plasma and milk. Cows were fed diets supplemented with 1000 IU of vitamin E/d from calving through the experimental period. At challenge, geometric mean DIM was 33 d. Each mammary quarter was diagnosed with an IMI and clinical mastitis at 24 and 48 h after challenge. The alpha-tocopherol concentrations in milk from challenged quarters were approximately 60% greater by 24 and 48 h after challenge than concentrations at prechallenge and 168 h postchallenge. Plasma alpha-tocopherol concentrations did not change after intramammary challenge. The alpha-tocopherol in plasma and milk was correlated at 48 and 168 h postchallenge but not at prechallenge or 24 h postchallenge. Milk alpha-tocopherol and SCC were correlated positively across all sample periods. Milk fat and milk alpha-tocopherol concentrations were correlated at each sample period except 24 h postchallenge. Increases in milk alpha-tocopherol during clinical mastitis were not correlated to milk production, DMI, or BSA concentration in milk. Changes in milk alpha-tocopherol concentration during clinical mastitis were similar to the dynamics of milk SCC.