Epidemiologic study of intramammary infections with Staphylococcus aureus during a control program in nine commercial dairy herds

Modeling Mastitis Risk Management Effects on Dairy Milk Yield and Global Warming Potential

Mastitis represents a significant challenge for dairy farming, resulting in economic losses and environmental impacts. This study assesses a model for the evaluation of the impact of mastitis on dairy productivity and Global Warming Potential (GWP) under diverse management scenarios. The model considers a range of factors, including bedding materials, milking systems, health surveillance, and overcrowding. The results of the simulation demonstrate that effective management, encompassing the utilization of sand bedding, and the presence of an annual herd health monitoring plan have the potential to reduce the prevalence of mastitis and enhance milk yield by up to 10% in milking parlors and 7% in automatic milking systems. At the herd level, the GWP ranged from 1.37 to 1.78 kg CO2eq/kg Fat- and Protein-Corrected Milk (FPCM), with the use of sand bedding resulting in a 14% reduction in GWP, while the utilization of non-composted manure-based materials led to an increase of 12%. The occurrence of overcrowding and a lack of adequate cleanliness in resting areas were found to have a markedly detrimental impact on both productivity and the environmental performance of cows. These findings illustrate the dual benefits of enhanced mastitis management, namely improved milk production and reduced environmental impact. They offer valuable insights for farmers and policymakers alike.

From One Heath to One Sustainability: The Role of Contagious Mastitis Pathogens in Decreasing the Dairy Herd Sustainability

Economic, social, and environmental sustainability are the results of efforts aiming to improve all aspects of milk production, respecting animal welfare and improving herd health. An epidemiological study was designed to assess the role of contagious pathogens (S. aureus and S. agalactiae) in a cohort of 120 dairy herds located in the southern regions of Italy. Milk quality was assessed using certified methods, and the prevalence of mastitis pathogens in bulk tank milk was determined using quantitative polymerase chain reaction. Welfare scores were assessed using a scoring card that has more than 100 items, including animal-based measurements. Statistical analyses were performed using general lineal model and logistic regression procedures. The results showed that S. aureus had a significant negative effect on the amount of milk nutrients delivered to the dairy plant, and on the level of welfare, whereas the presence of S. agalactiae did not show any significant association. The major risk factors associated with the presence of S. aureus were also identified to help prioritize control programs. These results support the "One Sustainability" approach, implying that an increase in animal productivity is related to the improvement of animal health and welfare and potentially leading to the mitigation of greenhouse gas emissions.

Innovative Elastomers with Antimicrobial Activity May Decrease Infection Risks during Milking

Contagious pathogens are very costly to dairy herds, and they may have zoonotic and reverse-zoonotic potentials and may contribute to the spread of antimicrobial resistance. One of the most important risk factors for spreading these infections is milking, when liner contamination may transfer the pathogens from infected to healthy cows. There is no effective protocol to prevent the transmission of infection without the segregation of infected cows. Recently, the availability of elastomers with patented antimicrobial components in their formulations has allowed the exploration of alternative methods to reduce the risk of infection. Two different types of elastomers (rubber and silicone) and nine different formulations were challenged with three major mastitis pathogens (S. aureus, S. agalactiae, and E. coli). The results that were obtained in this study were interesting and unexpected. Indeed, to our knowledge, this is the first study to show that basic rubber materials have intrinsic antimicrobial activity. Silicone elastomers did not exhibit the same levels of bactericidal activity, although they did exhibit some antibacterial capacity. A significant decrease in bacterial survival curves was observed for all the formulations tested when antimicrobial components were added. The different results observed for the various products are likely due to the different formulations and diverse manufacturing processes. The availability of these new materials that significantly reduce the bacterial load on the liner surface may reduce the risk of spreading intramammary infections during milking. This would be an important step forward in achieving global sustainability of dairy herds, consistent with the objectives of One Health, by reducing the risks of zoonotic diseases and antimicrobial treatments.

Early Milk Total and Differential Cell Counts as a Diagnostic Tool to Improve Antimicrobial Therapy Protocols

Mastitis is a major cause of antimicrobial treatments either during lactation or at drying off. From a One Health perspective, there should be a balance between the risk of IMI that may impair cow health and welfare and the reduction of antimicrobial usage to decrease antimicrobial resistance, as may happen when applying selective dry-cow therapy. This reduction may be achieved by an early and accurate diagnosis followed by prudent and rationale therapeutical protocols. This study aims to assess the accuracy of PLCC (neutrophils + lymphocyte count/mL) in identifying cows at risk of having IMI due to major pathogens (S.aureus, Str.agalactiae, Str.uberis, and Str.dysgalactiae), and to simulate the impact of this early diagnosis on the potential number of treatments using a decision-tree model. The results of this study showed that PLCC had an overall accuracy of 77.6%. The results of the decision-tree model based on data from the 12 participating herds, with an overall prevalence of major pathogens of 1.5%, showed a potential decrease in the number of treatments of about 30% (from 3.4% to 2.5%) when PLCC in early lactation (days 5-16) was used to identify cows at risk for major pathogens compared with using SCC at the first milk test (days 17-43). The study confirmed that it is possible to improve animal health and reduce the risk of antimicrobial use through early IMI detection based on PLCC and applying a rationale and prudent antimicrobial protocol.

First molecular characterization of capsule expression and antibiotic susceptibility profile of Staphylococcus aureus isolates from bovine mastitis in Jordan

Background and Aim: Bovine mastitis has long been considered the most important cause of economic losses in the dairy industry. Staphylococcus aureus is the most frequently isolated pathogen from bovine mastitis cases worldwide. Capsular polysaccharides (CPs) of serotype 5 (CP5) or serotype 8 (CP8) are the most prevalent capsule genotypes related to infections associated with S. aureus in humans. However, a variety of CPs has been reported in ruminants and other hosts. Information regarding the relationship between genotypic and phenotypic capsule variation and bovine mastitis in Jordan is scarce. Thus, we aimed to determine the prevalence of S. aureus capsule genotypes CP5 and CP8 in milk from bovine mastitis cases and the antimicrobial susceptibility profile of the recovered isolates in 27 dairy farms in Jordan. Materials and Methods: Staphylococcus aureus strains were isolated from bovine mastitis cases in two districts of Jordan. All S. aureus isolates were initially identified using conventional biochemical and microbiological methods. Subsequently, confirmation of the identity of S. aureus was performed by polymerase chain reaction (PCR) targeting nuc gene. Capsule polysaccharide typing was performed by PCR specific for CP5 and CP8. In addition, we assessed the antibiotic susceptibility profile of S. aureus isolates against commonly used antimicrobials by the disk diffusion method according to Clinical and Laboratory Standards Institute guidelines. Results: We collected 148 clinical isolates of S. aureus from bovine mastitis cases in the Zarqa (67.6%, n = 100) and Irbid (32.4%, n = 48) districts. Most isolates possessed capsule genotypes (91.3%), predominantly CP8 (88.6%). Only 8.7% of the isolates were nontypeable by PCR. In addition, we found statistically significant differences between the geographical region and the status of methicillin-resistant capsule genotypes (p < 0.05). The rates of resistance to β-lactam, macrolide, and fluoroquinolone antibiotics were very low, but resistance to tetracyclines was considerably high (22.3%). Significantly, mastitis isolates from Irbid showed a higher rate of resistance to ciprofloxacin (8.3% vs. 0%), while isolates from Zarqa showed a significantly higher rate of resistance to gentamicin (12.0% vs. 6.2%). Conclusion: We established associations between capsule genotypes and antimicrobial resistance and the pathogenic behavior of S. aureus isolated from bovine mastitis cases. Further studies are necessary to fully elucidate the role and mechanisms of capsular expression in the epidemiological and molecular variability of S. aureus in bovine mastitis.

Milk Quality and Safety in a One Health Perspective: Results of a Prevalence Study on Dairy Herds in Lombardy (Italy)

Mastitis is one of the major diseases of dairy cows that affects milk quality and quantity and increases the potential risk for the presence of antimicrobial residues (AR) in milk, which could lead to the development of antimicrobial resistance (AMR) among human pathogens. Even if the presence of AR in milk and milk products is low in many countries, the threat is not negligible and cannot be ignored. These problems may be investigated by applying a One Health approach, and this prevalence study aimed to estimate the risks for human health related to milk production applied to dairy herds in Lombardy. Three hundred thirty-one bulk tank milk samples were randomly collected and analyzed by CombiFoss 7 and MilkoScan 7 (milk quality, bacteria, and somatic cell count), an HPLC system coupled to a Q-Exactive Orbitrap (AR), and qPCR (contagious pathogens). The data were analyzed by a generalized linear model. The results showed a relatively high prevalence of contagious pathogens (S. aureus 28.1%; Str. agalactiae 7.3%; M. bovis 3%), which primarily affect milk nutritional components decreasing mainly milk fat content (range 1%-2.5%), but did not show them to be associated to an increase of the risk of antimicrobial residues. These latter ones were recovered only in 7/331 samples at concentrations far below official MLRs. The results support currently active surveillance programs' efficacy in reducing AR risks, which may be further improved by prioritizing them based on geographical area characteristics.

Retrospective cohort study of management procedures associated with dairy herd-level eradication of Streptococcus agalactiae in the Danish surveillance program

The aim of this observational retrospective cohort study was to identify management procedures that are associated with herd-level eradication of Streptococcus agalactiae in dairy herds. The objective was to compare herds that recovered from Strep. agalactiae with herds that remained infected with Strep. agalactiae on the basis of specific management procedures. Data from the Danish surveillance program for Strep. agalactiae, where all milk delivering dairy herds are tested yearly, were used to identify study herds. One hundred ninety-six herds that were classified in the program as infected with Strep. agalactiae, in both January 2013 and January 2014, were identified as study herds. These were followed until January 2017. One hundred forty-four herds remained infected every year until January 2017. Forty-six herds recovered from Strep. agalactiae after January 2014 (were tested negative continuously after January 2015, January 2016, or January 2017 and remained noninfected in the program from recovery until January 2017). Herd characteristics and management procedures were obtained through the Danish Cattle Database. Herd characteristics included herd size, yield, milking system, and bulk milk somatic cell count (SCC). Management procedures included the proportion of cows culled within 100 d after calving due to mastitis, the extent of diagnoses relative to the extent of mastitis treatments, the proportion of cows treated for mastitis during lactation, the proportion of cows treated for mastitis early in lactation, the proportion of cows treated at dry-off, and the median length of the dry period for cows receiving dry cow treatment. All variables were calculated on herd level. Multivariable logistic regression was used to analyze the association between herd infection status and management procedures. A higher proportion of culling due to mastitis within 100 d from calving was associated with a higher probability of herd-level recovery from Strep. agalactiae in herds with conventional milking system. For example, herds with conventional milking, a bulk milk SCC of 260,000 cells/mL, and 10% early culling due to mastitis had a recovery probability of 0.13, whereas similar herds with 20% early culling due to mastitis had a recovery probability of 0.15. A higher proportion of mastitis treatments within 250 d postcalving was associated with a higher probability of herd-level recovery for herds with a relatively high bulk milk SCC. For example, herds with conventional milking, a bulk milk SCC of 260,000 cells/mL, and 10% lactational mastitis treatments had a recovery probability of 0.12, whereas similar herds with 20% lactational mastitis treatments had a recovery probability of 0.15. Herds with a low bulk milk SCC (<220,000 cells/mL) combined with a low proportion of lactational treatments (<0.2) had a relatively high probability of herd-level recovery (>0.2). Additional variables, including the proportion of dry cow treatments, were not associated with herd-level recovery from Strep. agalactiae.

MerTK negatively regulates Staphylococcus aureus induced inflammatory response via Toll-like receptor signaling in the mammary gland

Mastitis is the most commonly diagnosed infectious disease reducing milk yield and quality and is accompanied by mammary tissue damage in both humans and animals. Mastitis incurs welfare and economic costs as well as environmental concerns regarding treatment. Staphylococcus aureus (S. aureus) is a prevalent Gram-positive bacteria and a major cause of mastitis, however, pathogenesis of the intrinsic anti-inflammatory response in mammary tissues is still principally unknown. Our aim, in combatting the S. aureus induced inflammatory response in mammary tissues, was to elucidate the intrinsic anti-inflammatory role of MerTK signaling. Here, we demonstrate that Mer receptor tyrosine kinase (MerTK) regulates an intrinsic negative feedback to balance the over-reaction of the host defense system. S. aureus elicits toll-like receptors 2 and 6 (TLR2/TLR6) signaling pathways, subsequently recruiting TRAF6, whose ubiquitination is intricate to the downstream signaling including MAPKs and NF-κB. We observed that TLR2/TLR6 activation, in response to S. aureus, was concomitant with induced MerTK activation, leading to raised expression of suppressor of cytokine signaling 1 and 3 (SOCS1, SOCS3) in wild type mice mammary tissues and epithelial cells. Meanwhile, S. aureus infection in MerTK-/- mice showed significant increased phosphorylation of p65, IκBα, p38, JNK and ERK along with production of pro-inflammatory cytokines. Moreover, MerTK-/- evidently inhibited S. aureus induced phosphorylation of STAT1 and subsequent SOCS1/SOCS3 expression which are pivotal in the negative feedback mechanism for targeting TRAF6 to inhibit the TLR2/TLR6 mediated immune response. Taken together, our findings demonstrate the importance of MerTK in the regulation of the intrinsic feedback during the inflammatory response induced by S. aureus through STAT1/SOCS1/SOCS3 in mice mammary tissues and mice mammary epithelial cells (MMECs).

Current management practices and interventions prioritised as part of a nationwide mastitis control plan

The objectives of this study were to report performance and management data taken from a sample of UK dairy farms that have participated in the Agriculture and Horticulture Development Board Dairy Mastitis Control Plan (DMCP) and to identify important mastitis prevention practices that are not currently widely implemented. A total of 234 UK dairy herds were included in the study from which farm management and udder health data were collected. Herds were grouped according to their mastitis epidemiology and could be classed as (i) environmental dry period (EDP) (i.e. environmental pathogen with majority of infections being acquired during the dry period), (ii) environmental lactation (EL), (iii) contagious dry period (CDP) or (iv) contagious lactation (CL). The results of this study showed that many mastitis-related management practices that are generally considered to be important were not widely performed. A better understanding of those practices not widely adopted by UK dairy farmers at present may aid practitioners in identifying and overcoming potential barriers to improved mastitis control.

Pattern characterization of genes involved in non-specific immune response in Staphylococcus aureus isolates from intramammary infections

Staphylococcus aureus isolated from mammary gland are characterized by different genetic patterns. Ninety four isolates from 33 dairy herds were analyzed by the means of a microarray to investigate S. aureus virulence patterns and the distribution of genes believed to be involved in immune evasion. None of the 94 isolates considered were MRSA. However, 50% of the isolates belonged to complexes related to MRSA and to human diseases, while only about 25% of them can be considered as exclusively of bovine origin. The distribution of clonal complexes and the different gene patterns observed confirmed the presence of an influence of geographical localization. The assessment of the influence of genes related to immune evasion on quarter milk cell count showed as four of them showed to be significantly associated to an increase quarter milk SCC. These genes could be potential target for developing new vaccines against S. aureus.

Preparation and Preliminary Application of MAdCAM-1 Polyclonal Antibody in Dairy Cows with Subclinical Mastitis

MAdCAM-1 plays an important role in mediating immune response and inflammation. This study aimed to express and purify a fusion protein of MAdCAM-1 in prokaryotic cells and to prepare rat anti-bovine MAdCAM-1 polyclonal antibodies. Prokaryotic expression vector pGEX-4T-1-MAdCAM-1 and pET-28a-MAdCAM-1 were constructed, respectively. The above plasmids were transformed into BL21 Escherichia coli strain. These recombinant strains were induced by IPTG and identified by Western blot analysis and SDS-PAGE. Wistar rats were immunized with recombinant protein (pET-28a-MAdCAM-1) emulsified with Freund's adjuvant, and antibody titers were measured by indirect ELISA. Antibody titers reached the highest value (1:128,000) after the third immunization. Western blot showed that rat anti-bovine MAdCAM-1 polyclonal antibody can not only recognize recombinant MAdCAM-1 protein expressed in E. coli but also recognizes natural MAdCAM-1 protein extracted from bovine tissues. However, commercial anti-mouse MAdCAM-1 monoclonal antibodies did not recognize the recombinant MAdCAM-1 protein or natural protein, which indicated no cross-reactivity between bovine MAdCAM-1 and mouse MAdCAM-1. Real-time fluorescence quantitative polymerase chain reaction and Western blot analysis showed that MAdCAM-1 expression was limited in mammary lymphoid nodes of subclinical mastitis in dairy cows. We speculate that MAdCAM-1 expression is inconsistent in different periods of the dairy cows. The successful preparation of rat anti-bovine MAdCAM-1 polyclonal antibody and its preliminary application in dairy cows provide the foundation for further study of the mechanism of anti-inflammation of MAdCAM-1 in dairy cows with subclinical mastitis.

Staphylococcal enterotoxin H induced apoptosis of bovine mammary epithelial cells in vitro

Staphylococcal enterotoxins (SEs) are powerful superantigenic toxins produced by Staphylococcus aureus (S. aureus). They can cause food poisoning and toxic shock. However, their impact on bovine mammary epithelial cells (bMECs) is still unknown. In this study, the distribution of SE genes was evaluated in 116 S. aureus isolates from bovine mastitis, and the most prevalent genes were seh (36.2%), followed by sei (12.1%), seg (11.2%), ser (4.3%), sec (3.4%), sea (2.6%) and sed (1.7%). To better understand the effect of staphylococcal enterotoxin H (SEH) on bMECs, the seh gene was cloned and inserted into the prokaryotic expression vector, pET28a, and transformed into Escherichia coli BL21 (DE3). The recombinant staphylococcal enterotoxin H (rSEH) was expressed and purified as soluble protein. Bioactivity analysis showed that rSEH possessed the activity of stimulating lymphocytes proliferation. The XTT assay showed that 100 μg/mL of rSEH produced the cytotoxic effect on bMECs, and fluorescence microscopy and flow cytometry analysis revealed that a certain dose of rSEH is effective at inducing bMECs apoptosis in vitro. This indicates that SEs can directly lead to cellular apoptosis of bMECs in bovine mastitis associated with S. aureus.

Update on control of Staphylococcus aureus and Streptococcus agalactiae for management of mastitis

The primary method of spread for S agalactiae and S aureus is from cow to cow, so prevention focuses on within and between herd biosecurity to reduce or eliminate the reservoir of infection. S agalactiae is an obligate pathogen of the mammary gland, whereas S aureus is more widespread on other cow body sites and in the environment. Both organisms cause persistent infections, with S agalactiae typically causing higher SCC and bacteria counts in milk. Conventional methods of detection through culture perform well at the cow level. In bulk tanks, augmented procedures should be considered. PCR methods show promise of high sensitivity and specificity, at both the cow and bulk tank level. In developed dairy industries, prevalence of infection has decreased dramatically over the past 30 years for S agalactiae. For S aureus, the herd level of infection remains very high, although with rigorous, consistent application of control measures, within-herd prevalence has decreased. Because the milking time is the primary period for new IMI, it is the focal point of most prevention activities. Premilking and postmilking teat disinfection and proper stimulation and milk-out with adequately functioning equipment are key factors. There is growing evidence that the use of milking gloves is an integral part of contagious mastitis control and the production of high-quality milk. Treatment success is dramatically different between the 2 pathogens. For S agalactiae, eradication can be completed rapidly through a culture and treatment program with minimal culling. For S aureus, treatment success, particularly during lactation, is often disappointing and depends on cow, pathogen, and treatment factors. These factors should be reviewed prior to initiating any treatment to determine the potential for cure. Blanket dry cow therapy and strategic culling are important control procedures for contagious mastitis pathogens. Maintaining a closed herd or, at minimum, adhering to clearly defined biosecurity protocols is critical to reduce risk of reintroduction of S agalactiae or the addition of new, potentially more virulent strains of S aureus to endemic herds.

Protective effect of recombinant staphylococcal enterotoxin A entrapped in polylactic-co-glycolic acid microspheres against Staphylococcus aureus infection

Staphylococcus aureus is an important cause of nosocomial and community-acquired infections in humans and animals, as well as the cause of mastitis in dairy cattle. Vaccines aimed at preventing S. aureus infection in bovine mastitis have been studied for many years, but have so far been unsuccessful due to the complexity of the bacteria, and the lack of suitable vaccine delivery vehicles. The current study developed an Escherichia coli protein expression system that produced a recombinant staphylococcal enterotoxin A (rSEA) encapsulated into biodegradable microparticles generated by polylactic-co-glycolic acid (PLGA) dissolved in methylene chloride and stabilized with polyvinyl acetate. Antigen loading and surface properties of the microparticles were investigated to optimize particle preparation protocols. The prepared PLGA-rSEA microspheres had a diameter of approximately 5 μm with a smooth and regular surface. The immunogenicity of the PLGA-rSEA vaccine was assessed using mice as an animal model and showed that the vaccine induced a strong humoral immune response and increased the percent survival of challenged mice and bacterial clearance. Histological analysis showed moderate impairment caused by the pathogen upon challenge afforded by immunization with PLGA-rSEA microspheres. Antibody titer in the sera of mice immunized with PLGA-rSEA microparticles was higher than in vaccinated mice with rSEA. In conclusion, the PLGA-rSEA microparticle vaccine developed here could potentially be used as a vaccine against enterotoxigenic S. aureus.

Study of Staphylococcus aureus collected at slaughter from dairy cows with chronic mastitis

Staphylococcus aureus is one of the most important pathogens associated with bovine mastitis. Recent studies have shown that Staph. aureus strains may differ in virulence, and in their ability to disseminate across commercial dairy herds. The goal of this study was to determine whether Staph. aureus isolates differed in their ability to colonize mammary tissue, and whether such differences could be related to molecular characteristics. Quarter milk and mammary tissues of 22 cows from two dairy herds, were collected at slaughter and bacteriological analysis was performed. All Staph. aureus isolates were characterized by Pulsed Field Gel Electrophoresis (PFGE) and microarray. Overall 45 mammary quarters were infected and 20 Staph. aureus isolates were identified. The bacteria were mostly recovered from both milk and tissue of the same quarter in significantly higher numbers from herd A cows compared with herd B. Molecular characterization of the isolates showed distinct PFGE profiles for isolates from each herd. Differences in virulence factors between herds A and B isolates were evidenced The genes for enterotoxin D, J and R were present in herd A, those for G, I, N, M, O and U were shown in herd B, whilst both components of the leukocidin lukD/E genes were only carried by herd A isolates. Furthermore, all herd A isolates showed β-haemolysin activity, which was absent in all but one isolate from herd B. Therefore our data indicate that Staph. aureus isolates showing differences in their ability to disseminate and colonize across quarters, also have significantly different virulence characteristics.

Efficacy of immunization against bovine mastitis using a Staphylococcus aureus avirulent mutant vaccine

Bovine mastitis is responsible of major economic losses on dairy farms worldwide. In Argentine dairy herds, Staphylococcus aureus is the main causative agent of the disease. The ineffectiveness of some current practices to control S. aureus infections, often leads to a chronic and recurrent infection with persistent bacterial reservoir within a herd. Vaccination against S. aureus seems to be a rational approach for the control of the disease. In the present study, we investigate the response of dairy heifers after a combined immunization schedule with the avirulent mutant RC122 S. aureus vaccine. Vaccinated and non-vaccinated heifers were challenged 40 days after calving with the parental virulent strain. After challenge, and during the study period, milk bacterial recovery was significantly higher in non-vaccinated heifers than vaccinates. Importantly, inoculated bacteria could not be isolated from the milk of vaccinated heifers until 72 h after challenge, and the overall percentage of infected quarters in these animals was significantly lower. An increase in the level of specific IgG was observed in blood and milk of vaccinated heifers during the trial. At calving, IgG(2) was the main antibody isotype found in blood. Immune sera from vaccinated heifers increased phagocytosis over sera from non-vaccinated heifers and were able to opsonize heterologous S. aureus strains. Results demonstrated that immunization of dairy heifers with strain RC122 was able to elicit a significant opsonic antibody production in blood and milk and provides protection by a significant reduction in bacterial shedding after challenge.

Relationship between S. aureus gene pattern and dairy herd mastitis prevalence

The importance to evaluate Staphylococcus aureus virulence analysing the combination of virulence genes is largely recognised, and the recent availability of simplified microarray tools allows performing these analyses also in the dairy field. The combined availability of herd-specific S. aureus mastitis prevalence data, isolates from these herds, and microarray technology offered the opportunity to investigate the relationship between S. aureus genetic pattern and their prevalence among dairy herds. Eleven commercial dairy herds following a S. aureus control programme were enrolled in the study, and 33 S. aureus isolates were collected from these herds. Diagnostic DNA microarrays based on the array-tube platform were used for genotyping of staphylococcal DNA. The genetic analysis of the 157-genes microarray showed as only 19 genes were present in all the isolates considered, and among them the genes coding for the leukocidin subunits (LukF, LukS and LukY), haemolysins (hla, hld and an unnamed haemolysin) and enterotoxin X. Several genes considered in the arrays were absent in all the isolates, including the ones encoding the resistance to most of the antimicrobials, except for tetracycline. In our isolates, some agr alleles were never identified (B-III, C-III, D-III, C-IV and D-IV). The comparison of epidemiological data with the genetic pattern suggests that agr type II is associated to the most diffusive isolates, being recovered from the largest number of herds and with the highest frequency. Microarray technique showed to be a useful method to assess the characteristics of virulence of S. aureus isolated in dairy herds and to investigate the relationship with the prevalence of the microorganism. These results support previous evidence that specific gene patterns could be associated to S. aureus mastitis.

Relationship between virulence factor genes in bovineStaphylococcus aureussubclinical mastitis isolates and binding to anti-adhesin antibodies

Staphylococcus aureusis the most common aetiologic agent of contagious bovine mastitis. It is characterized by a wide array of virulence factors. The differences among strains jeopardize the development of effective vaccines againstStaph. aureusmastitis. We tested the immunogenicity of a peptide subunit vaccine coding for three different adhesion factors, fibrinogen-binding protein (Efb), fibronectin-binding protein A (FnbpA) and clumping factor A (ClfA). Then we evaluated the influence of some virulence factors on the ability of specific anti-adhesin antibodies to react with sixteenStaph. aureusstrains isolated from bovine subclinical mastitis. Immunization with the recombinant adhesins stimulated a strong humoural (IgG and IgA) and mucosal IgA immune response in all animals tested. Hyperimmune serum recognized with diverse efficiency the sixteenStaph. aureusstrains and this circumstance correlated well with the level of expression of adhesins. Among the different virulence factors considered to classify strains,spagene polymorphisms showed the strongest influence on isolate reactions to hyperimmune serum. Our results indicate the importance of a disease- and environment-specific analysis of isolates. Thus, as opposed to other pathogens to obtain an effective vaccine we should characterize multiple strains and identify the prevalent virulence factors expressed.

The role of teat skin contamination in the epidemiology ofStaphylococcus aureusintramammary infections

Knowledge of the epidemiological pattern and the potential sources of infections is important to controlStaphylococcus aureusin dairy herds. This paper reports the results of a study applying both pulse field gel electrophoresis (PGFE) and the assessment of a selected number of virulence genes to investigate the role of teat skin onStaph. aureustransmission among cows and on the contamination of milk. Overall 61 isolates were considered, 23 from teat skin, 33 from milk samples and 5 from curd samples. Teat swabs were taken in five herds, but in only three of them couldStaph. aureusbe isolated. Curd was sampled in three herds, butStaph. aureuscould be isolated in only two herds. The distribution of isolates among herds confirmed the presence of herd-specificStaph. aureusstrain in most of the herds. The same pattern was observed in teat skin samples, in quarter milk samples, and in the curd samples. Our findings are consistent with other studies showing the role of teat skin as a potential reservoir. Moreover,Staph. aureuswas isolated from teat skin of confirmedStaph. aureus-negative cows that were segregated from infected ones. Our findings also suggest that some strains have higher chances to survive on teat skin and therefore to increase the risk for contamination of milk and milk products due to the persistence of intramammary infections.

Development of a highly sensitive and specific assay to detect Staphylococcus aureus in bovine mastitic milk

Diagnosis of udder infections with Staphylococcus aureus by bacteriological milk testing of quarter milk samples is often not satisfactory. To get reliable results, repeated sampling is necessary, which is normally too expensive. Therefore, we developed a test that allows the highly specific detection of Staph. aureus in bovine milk samples at very low concentrations. It is based on a fast procedure to prepare bacteria from milk, followed by DNA extraction and quantitative PCR. The whole analysis is done within 5 h. For clinical milk samples, the analytical sensitivity of the assay was 50.7 times and 507 times higher than conventional bacteriology with 100 and 10 microL, respectively. The diagnostic specificity was 100%. The test is further characterized by a low intra- and interassay variability as well as by a good recovery of Staph. aureus from raw milk. Furthermore, a high correlation (R = 0.925) between the agar plate counts and the quantitative PCR methodology over the whole range of measurement was found. In addition, our test revealed considerably more positive results than bacteriology. Due to its favorable properties, the assay might become an important diagnostic tool in the context of bovine mastitis caused by Staph. aureus.

Protective effects of recombinant staphylococcal enterotoxin type C mutant vaccine against experimental bovine infection by a strain of Staphylococcus aureus isolated from subclinical mastitis in dairy cattle

Staphylococcus aureus is one of the main etiological agents of bovine mastitis; however, antibiotics that are effective against bovine strains of S. aureus are not currently available. Staphylococcal enterotoxin type C (SEC), a superantigen, is the enterotoxin most frequently expressed by bovine strains of S. aureus and one of immunogenic determinants. The purpose of this study was to evaluate the protective effectiveness of recombinant SEC mutant vaccine (MastaVactrade mark) against experimentally induced bovine infection. Three representative SEC secreting strains were selected from 9 candidate isolates that showed various intensities of pathogenicity on mice and inoculated into 5 lactating dairy cattle at a concentration of 50-5.0x10(8) CFU per quarter. The optimal experimental bovine subclinical mastitis model was produced by inoculation with 50 CFU of S. aureus 409 per quarter, a level which was not lethal to mice. After the experimental model was determined, other 3 cattle were intramuscularly administered three doses of vaccine at day 0, at 2 wks and at 6 wks. Nine quarters of 3 vaccinated cattle and 8 quarters of 3 control cattle were then challenged with S. aureus 409. An SEC-specific ELISA test conducted at 4 wks post-immunization confirmed the presence of a high antibody titer against SEC in all vaccinated cattle. The somatic cell counts from the vaccinated group remained relatively low, whereas those of control group increased significantly after challenge with S. aureus. After challenge, S. aureus was not isolated from any cattle in the vaccinated group, whereas it was isolated from 75% of the cattle in the control group. These results indicate that recombinant SEC mutant vaccine had a protective effect against S. aureus intramammary infection in lactating cattle.

Experimental trial in heifers vaccinated with Staphylococcus aureus avirulent mutant against bovine mastitis

Staphylococcus aureus, is the most frequently isolated pathogen from cases of bovine mastitis. Vaccination against S. aureus seems to be a rational approach for the control of staphylococcal mastitis. In the present work we evaluate the response of heifers vaccinated with a S. aureus avirulent mutant to the intramammary challenge with a S. aureus virulent strain. Clinical signs, production of milk, shedding of S. aureus cells, somatic cell count (SCC) and antigen-specific IgG in blood and milk, were determined. Two subcutaneous doses of a culture of the mutant, used as vaccine, was administered to four pregnant heifers 30 and 10 days before calving. The vaccinated heifers and four non-vaccinated were challenged 10 days after calving with the homologous virulent S. aureus strain, which was inoculated by intramammary route into two quarters of each animal. No local tissue damage was observed due to the administration of the vaccine. A significantly increase of specific IgG to S. aureus RC122 was detected in blood and milk of vaccinate heifers as well as a slight increase in daily milk yield during the trial. No significant difference on shedding of bacteria in milk and SCC were found among groups. In conclusion, vaccination of heifers before calving by an avirulent mutant vaccine of S. aureus, induced specific and significant antibody responses and provide better post-challenge conditions in vaccinated heifers.

Characterization of cell wall associated proteins of a Staphylococcus aureus isolated from bovine mastitis case by a proteomic approach

Staphylococcus aureus causes different pathologies in humans and animals. In particular, it is involved in intramammary infections in cows, causing economic losses and milk-safety problems. Although it is well-known that surface components (proteins and capsular polysaccharides) and exotoxins are virulence factors involved in the pathogenesis of bovine mastitis, less is known about the precise biochemical identity of such molecules. Therefore, mapping of surface proteins using specific disease- and environment-isolates provides a benchmark for strain comparison of pathogens with different pathogenic characteristics and antibiotic resistance mechanism and can aid in defining specific vaccine and therapeutic targets. In this study, we used a proteomic approach on protein extracts of lysostaphin-treated S. aureus in isotonic conditions, to produce a reproducible and well resolved 2-D electrophoresis (2-DE) reference map of surface associated proteins of isolated S. aureus from a case of bovine mastitis. The most abundant protein components were identified by Matrix assisted laser desorption ionisation-time of flight (MALDI-TOF) mass spectrometry.

Mucosal genetic immunization against four adhesins protects against Staphylococcus aureus-induced mastitis in mice

Staphylococcus aureus is the most common etiologic agent of mastitis in bovines and a major cause of economic losses in the dairy industry. Since adhesins, that anchor bacteria to the extracellular matrix (ECM), are among the most important S. aureus virulence factors, we used four adhesion factors (fibrinogen binding protein, fibronectin binding protein A, clumping factor A and collagen adhesin) as target in a DNA vaccine. Intranasal immunization with a pDNA mixture coding the four adhesins, triggered significant levels of specific serum and mucosal Ig that inhibited S. aureus adhesion to cow mammary gland epithelial cells in vitro. Splenocytes of immunized mice challenged in vitro with S. aureus extracts showed a strong proliferative response. Finally, immunized mice were significantly protected against intramammary challenge with S. aureus. Our data confirm the feasibility of a genetic mucosal vaccine targeting S. aureus adhesins and prompt further study to test the efficacy in preventing cow mastitis.

Role of several Staphylococcus aureus virulence factors on the inflammatory response in bovine mammary gland

Staphylococcus aureus causes many serious diseases in humans and animals, and it is the most common aetiologic agent of contagious bovine mastitis. The bacteria produce several virulence factors and the importance of evaluating the combination of these virulence factors has been recently emphasized. In study, the combination of several virulence factors: coagulase gene (coa), protein A gene (spa), collagen-binding protein gene (cna), fibrinogen-binding protein gene (efb), Panton-Valentin leukocydin gene (pvl) and enterotoxins (sea,seb, sec, sed, see, seg, seh, sei, sej) was considered. The analysis of the relationship between presence/absence of the different genes and the udder inflammatory response measured by milk somatic cell counts was performed by general linear models and logistic regression. The classification of isolates in clusters by virulence genes combinations showed that at least one cluster induced a higher inflammatory response. Moreover, the analysis of the association between virulence genes and the presence of a subclinical mastitis showed the role of spa and sej gene as risk factors. These results support that the development of subclinical mastitis could be related to strains characteristics and to the expression of specific combinations of the virulence factors.

Multilocus sequence typing of intercontinental bovine Staphylococcus aureus isolates

A total of 258 bovine-associated Staphylococcus aureus isolates from the United States, Chile, and the United Kingdom, plus the reference isolate S. aureus Newbould 305 (NCIMB 702892), were analyzed by multilocus sequence typing (MLST). A collection of previously characterized United Kingdom isolates were also included in the analysis. The results demonstrated that MLST is suitable for the differentiation of bovine S. aureus isolates from various sites (milk, teat skin, milking machine unit liners, hands, and bedding) and countries. The theory of the host specificity of S. aureus is supported by the detection of a previously undescribed clonal complex that comprised 87.4% of the isolates studied, with representatives from all geographic locations investigated. This suggests that a single clonal group has achieved a widespread distribution and is responsible for the majority of infections. Some sequence types (STs; ST25, ST115, ST124, and ST126) demonstrated site specificity, as they were significantly (P < 0.05) associated with milk or teat skin.

Nasal carriage of Staphylococcus aureus in dairy sheep

The purpose of this study was to assess the prevalence of Staphylococcus aureus nasal carriage of dairy sheep in farms producing cheeses manufactured with raw ewe's milk. The study showed that 29% of ewes carried S. aureus in their nares. The genetic diversity of the 136 isolates recovered from the anterior nares of the ewes, from the ambient air of the milking parlour and from cheeses was investigated using pulsed-field gel electrophoresis (PFGE) of DNA SmaI digests. The genotyping results showed that 75 out of 106 isolates recovered from nasal carriage in dairy sheep belonged to a dominant pattern (previously named OV) and a genetically related pattern (named OV'). The same profile (OV or OV') was found in the ambient air and cheeses, suggesting a continuum between isolates within these different compartments.

Epidemiological Study of Non-contagious Intramammary Infections in Nine Commercial Dairy Herds following a Staphylococcus aureus Control Programme

Changes in prevalence in intramammary infection, by pathogen type, in herds applying a stringent contagious mastitis control programme was studied. Enrollment of 1651 lactating cows and collection of milk samples was made in this ancillary study to a cohort study of the dynamics of mastitis prevalence after adoption of a strict contagious mastitis control programme that targeted the elimination of mastitis caused by Staphylococcus aureus. Nine commercial dairies in Italy were used. Aseptic collection of milk samples from all lactating cows was performed at the time of enrollment, from all cows within 7-14 days of entering the lactating herd after the date of enrollment, and from all lactating cows at 2, 4, 7, 10 and 14 months after the date of enrollment. Prevalence of intramammary infection by pathogen type was determined from culture of milk samples. Application of the strict contagious mastitis programme did not lead to an increased risk of non-contagious mastitis. The risk of coliform, environmental streptococcal and coagulase-negative staphylococcal intramammary infections decreased after adoption of the programme. The data reported herein indicate that the overall risk for any intramammary infections decreases with adoption of a strict contagious mastitis programme, and that such a programme therefore does not necessarily lead to an increase in environmental mastitis.