Effect of Carprofen Treatment Following Experimentally Induced Escherichia coli Mastitis in Primiparous Cows

Acute Escherichia coli mastitis is one of the major sources of economic loss in the dairy industry due to reduced milk production, treatment costs, discarded milk, and occasional fatal disease. Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used as adjunctive therapy to antibiotics. The objective of the current study was to evaluate the effect of carprofen treatment following infusion of Escherichia coli into the mammary glands of primiparous cows during the periparturient period. Severity of mastitis was scored based on the average milk production in the uninfected quarters on d +2 postinoculation and a clinical severity score. Carprofen was administered intravenously at 9 h postchallenge, when clinical signs of mastitis appeared. In previous work, efficacy of NSAIDs was mainly evaluated using clinical symptoms. In the present study, the effect of carprofen on innate immune response was also assessed by quantification of inflammatory mediators. All primiparous cows reacted as moderate responders throughout the experimental period. Primiparous cows were intramammarily inoculated with 1 x 10(4) cfu of E. coli P4:O32 in 2 left quarters. Analysis of blood and milk parameters, including IL-8, complement component C5a, lipopolysaccharide-binding protein (LBP), soluble CD14, prostaglandin E2, and thromboxane B2 was performed from d 0 to d +6 relative to intramammary inoculation. Rectal temperature in carprofen-treated animals was lower than in control animals at 3 and 6 h posttreatment. Treatment also restored the decreased reticulorumen motility that occurs during E. coli mastitis to preinfection levels faster than in control animals. Carprofen treatment resulted in an earlier normalization of the clinical severity score. Eicosanoid (prostaglandin E2 and thromboxane B2) production in milk tended to be inhibited by carprofen. No significant differences in the kinetic patterns of somatic cell count, IL-8, complement component C5a, LBP, and soluble CD14 were observed. In conclusion, carprofen treatment improved general clinical condition by effective antipyrexia and restoration of reticulorumen motility but did not significantly inhibit eicosanoid production. Carprofen treatment did not result in a significant decrease of chemotactic inflammatory mediators, IL-8 and C5a, and early innate immune molecules, sCD14 and LBP. Therefore, major modulatory effects from NSAID administration were not observed in this mastitis model, although a larger study might confirm some apparent trends obtained in the present results.

Increase of Escherichia coli Inoculum Doses Induces Faster Innate Immune Response in Primiparous Cows

The objective of the current study was to evaluate the dynamics of infection and the immunological response to varying numbers of Escherichia coli injected into the mammary glands of primiparous cows during the periparturient period. Primiparous cows have been shown to be more resistant to intramammary E. coli challenge, and an increase of the inoculum dose by 2 log10 units induced a more rapid clinical response and clearance of the organisms. Recognition of lipopolysaccharide (LPS) is a key event in the innate immunity response to gram-negative infection and is mediated by the accessory molecules CD14 and LPS-binding protein (LBP). Primiparous cows were inoculated with 1 x 10(4) (Group A; n=8) or 1 x 10(6) (Group B; n=8) cfu E. coli P4:O32 in their 2 left quarters during the periparturient period. Clinical examination and analysis of blood and milk parameters, including IL-8, complement fragment 5a (C5a), LBP, and soluble CD14 (sCD14), were performed from d -4 to d +3 relative to infection. Primiparous cows in Group B initiated a more rapid clinical response following intramammary infection (IMI), resulting in typical clinical signs and changes in blood and milk parameters approximately 3 h earlier compared with primiparous cows in Group A. Based on average milk production in the noninfected quarters on d +2 postinoculation, all heifers reacted as moderate responders. Distinct differences in the kinetic patterns of rectal temperature, somatic cell count (SCC), IL-8, C5a, LBP, and sCD14 were observed between both groups during the early phase of inflammation. Both C5a and IL-8 increased before cellular influx into the infected glands, followed by increases in sCD14 and LBP. In conclusion, primiparous cows are able to clear an intramammary E. coli infection efficiently. Moreover, increasing the inoculum dose induces a more rapid inflammatory reaction, mainly because of early activation of the innate host immune response.

Escherichia coli and Staphylococcus aureus elicit differential innate immune responses following intramammary infection

Staphylococcus aureus and Escherichia coli are among the most prevalent species of gram-positive and gram-negative bacteria, respectively, that induce clinical mastitis. The innate immune system comprises the immediate host defense mechanisms to protect against infection and contributes to the initial detection of and proinflammatory response to infectious pathogens. The objective of the present study was to characterize the different innate immune responses to experimental intramammary infection with E. coli and S. aureus during clinical mastitis. The cytokine response and changes in the levels of soluble CD14 (sCD14) and lipopolysaccharide-binding protein (LBP), two proteins that contribute to host recognition of bacterial cell wall products, were studied. Intramammary infection with either E. coli or S. aureus elicited systemic changes, including decreased milk output, a febrile response, and induction of the acute-phase synthesis of LBP. Infection with either bacterium resulted in increased levels of interleukin 1beta (IL-1beta), gamma interferon, IL-12, sCD14, and LBP in milk. High levels of the complement cleavage product C5a and the anti-inflammatory cytokine IL-10 were detected at several time points following E. coli infection, whereas S. aureus infection elicited a slight but detectable increase in these mediators at a single time point. Increases in IL-8 and tumor necrosis factor alpha were observed only in quarters infected with E. coli. Together, these data demonstrate the variability of the host innate immune response to E. coli and S. aureus and suggest that the limited cytokine response to S. aureus may contribute to the well-known ability of the bacterium to establish chronic intramammary infection.

The complement in milk and defense of the bovine mammary gland against infections

The mammary gland of dairy cows, which is prone to infection by various bacteria, mobilizes local and systemic immune defenses to cope with pathogens. The complement system plays an important part in the innate immunity against microorganisms through its bactericidal, opsonic, and phlogistic functions. The amount of the complement in the milk of healthy glands of dairy cows is low. Moreover, the classical pathway of activation is not functional because of a shortage in C1q. By contrast, the alternative pathway is active, deposits C3b and C3bi on bacteria, and generates amounts of C5a which are highly variable among cows. A slight inhibition of the bactericidal/hemolytic activities, of the deposition of C1q on bacteria, and of the phlogistic activity of C5a makes milk a rather anti-inflammatory fluid. The inhibitory activity does not involve C3b/ C3bi deposition on bacteria, nor the generation of C5a by the alternative pathway. When inflammation develops, the blood-derived complement components overcome the inhibitions and complement-dependent bactericidal, opsonic and phlogistic activities may be high in milk. Further research is necessary to evaluate the contribution of C5a to the recruitment of leukocytes in the mammary gland, and to specify the links between the complement system and the response of resident cells (leukocytes and mammary epithelial cells) to infection stimulus. This will help to define the contribution of the complement system to resistance against mastitis, and could help to differentiate animals more or less resistant to this frequent and costly disease.

Mobilization of neutrophils and defense of the bovine mammary gland

The leucocytes present in normal milk are not very efficient in preventing infection, because very small numbers of bacteria are able to induce infection experimentally. The mobilization of phagocytes from the blood to milk appears crucial in coping with the expansion of the bacterial population in the mammary gland. Important parameters for the outcome of mammary infections are the bactericidal efficiency of neutrophils and the antiphagocytic and cytotoxic properties of the invading bacteria, but several studies have shown that the promptness and the magnitude of the initial recruitment of neutrophils by the infected mammary gland have a profound influence on the severity and the outcome of mastitis. This is an incentive for studying the mechanisms behind the mobilization of neutrophils to the mammary gland. Although milk macrophages may play a role in the triggering of the inflammatory response, studies on several responses to infections at various epithelium sites strongly suggest that epithelial cells are capable of responding to bacterial intrusion and play a major part in the initiation of inflammation. A better knowledge of the effector cells and of the mediators involved in the mobilization of neutrophils could help in devising strategies to modulate this important determinant of milk quality and udder defense.

Assessment of the Opsonic Activity of Purified Bovine sIgA Following Intramammary Immunization of Cows with Staphylococcus aureus

The phagocytosis of Staphylococcus aureus by bovine polymorphonuclear neutrophils (PMN) requires the presence of antibodies. Among the major isotypes of bovine antibodies, IgG2 and IgM are considered opsonic for bovine PMN. However, the role of purified bovine secretory IgA (sIgA) as an opsonin has not been assessed. In the present study, IgG2 were obtained from serum and sIgA, IgG1, and IgM were purified from the colostrums of three cows intramammarily immunized with heat-killed Staphylococcus aureus. The Ig preparations were assayed for specific antibodies, and the opsonic capacity of every isotype was investigated. Despite the presence of antibodies, we observed no distinct chemiluminescence response of PMN stimulated with sIgA- or IgG1-opsonized S. aureus, whereas IgM or IgG2 bound to bacteria induced a marked chemiluminescence response. Moreover, the counting of internalized bacteria per PMN after phagocytosis revealed a low uptake of S. aureus opsonized with sIgA or IgG1, in contrast to IgM or IgG2, which triggered efficient ingestion of bacteria. Priming of neutrophils by TNF-alpha, IFN-gamma, or C5adesArg did not promote an oxidative burst or uptake of sIgA-opsonized S. aureus to a greater extent than with IgG1-opsonized bacteria. Furthermore, analysis of uningested bacteria by flow cytometry after incubation with PMN showed a preferential uptake of IgM-opsonized S. aureus by PMN and only few sIgA-positive stained bacteria were PMN-associated. These experiments indicate that sIgA, like IgG1 and unlike IgM or IgG2, could not be considered as a major opsonin for phagocytosis of S. aureus by bovine blood PMN.

Leucotoxic activities of Staphylococcus aureus strains isolated from cows, ewes, and goats with mastitis: importance of LukM/LukF'-PV leukotoxin

Among the toxins that Staphylococcus aureus is able to secrete, bi-component toxins named leukotoxins target specifically leukocytes, mainly phagocytic cells. Isolates from cows, goats and ewes with mastitis were selected on the basis of the presence or not of the genes encoding the recently described LukM/LukF'-PV leukotoxin. Of the 128 isolates tested, 126 had moderate to high leukotoxic activity to bovine polymorphonuclear cells (PMN). The supernatants of lukM-positive isolates were much more leukotoxic than the supernatants of lukM-negative isolates: mean leukotoxic titers were 122 versus 20 and 581 versus 26 for isolates of bovine and caprine origin, respectively. Among lukM/lukF'-PV positive isolates, those of caprine and ovine origins were more leukotoxic than were isolates of bovine origin (P < 0.01). The two most abundant proteins in the culture supernatant of a highly toxic isolate were purified and identified as the two components of LukM (LukM and LukF'-PV) on the basis of their molecular mass, N-terminal amino acid sequence, and high synergistic activity. LukM/LukF'-PV induced the flattening of bovine PMN at a concentration as low as 3.6 ng/ml (0.1 nM). A higher concentration (18 ng/ml) was necessary to produce the same effect on caprine or ovine PMN. Affinity-purified antibodies to LukM or to LukF'-PV neutralized the leukotoxic effect of all the culture supernatants. They neutralized with the same efficiency the toxic activity of supernatants from lukM/lukF'-PV positive or negative isolates. These results establish that LukM/LukF'-PV is very active on PMN of ruminants and suggest that this leukotoxin could be the most active leukotoxin produced by mastitis isolates. They prompt further studies to delineate the contribution of LukM/LukF'-PV to the pathogenesis of mastitis in ruminants and the protective effect of antibodies to this leukotoxin.

Milk complement and the opsonophagocytosis and killing of Staphylococcus aureus mastitis isolates by bovine neutrophils

Phagocytosis of bacteria by bovine polymorphonuclear neutrophils (PMN) has long been regarded as essential for host defense against mastitis infection. Complement-mediated opsonisation by complement component 3 (C3) binding is an important component of the innate immune system. We investigated the role of milk complement as an opsonin and its involvement in the phagocytosis and killing of Staphylococcus aureus isolates from cases of bovine mastitis by bovine blood PMN. We show that deposition of milk C3 component occurred on six different isolates of S. aureus and that the alternative pathway was the sole complement pathway operating in milk of uninflamed mammary gland. This deposition was shown to occur at the same location as the capsule, but not on capsular antigen. Milk complement enhanced the chemiluminescence response of PMN induced by S. aureus. Nevertheless, the association of S. aureus to cells and the overall killing of bacteria by bovine PMN were not affected by the presence of milk complement. Therefore, as all milk samples contained antibodies to capsular polysaccharide type 5 and to other surface antigens, it is likely that milk antibodies were responsible for these two phagocytic events. Results of this study suggest that the deposition of milk complement components on the surface of S. aureus does not contribute to the defence of the mammary gland against S. aureus.

Bovine milk fat globules do not inhibit C5a chemotactic activity

The C5a complement fragment is a potent inflammatory molecule but its contribution to the inflammatory response of the mammary gland remains uncertain. One of the unresolved questions is the possible interference of whole milk with C5a. In this study, the chemotactic activity ofpurifled bovine C5a was tested in the presence of whole or skimmed milk. Milk from healthy glands acted as a chemoattractant, which could mask any inhibitory effect on C5a activity. To circumvent milk activity, washed milk fat globules were incubated with optimal (1 nM) or suboptimal (0.1 nM) concentrations of C5a, and the eventual chemoattractant activity was measured. There was no reduction in C5a-induced migration through a polycarbonate filter or shape-change of neutrophils. The concentrations of C5a determined by ELISA in the fluid phase were not reduced after incubation with the fat globules. It can be concluded that bovine milk fat globules do not trap or degrade C5a. Although these results do not explain the inhibitory effect of whole milk in the C5a-induced recruitment of neutrophils in milk, they suggest that milk does not inhibit the second major activity of C5a (apart from chemotaxis), i.e. the stimulation of phagocytic and bactericidal activities of neutrophils.

Complement factor B and the alternative pathway of complement activation in bovine milk

The contribution of the alternative pathway of complement activation to the capacity of normal milk to deposit C3 fragments on bacteria was tested by attempting to block C3 deposition with antibodies to the alternative pathway component factor B (fB). Factor B was purified and antibodies of the IgY class, which does not activate mammalian complement, were obtained from the egg yolk of immunized laying hens. These antibodies specifically inhibited the deposition of C3. This inhibition and the absence of deposition of C4 demonstrated that C3 deposition in normal milk resulted from the activation of the alternative pathway. Antibodies raised in rabbit were used to develop an ELISA for measuring fB concentrations in milk. The mean concentration of fB was 2.06 microg/ml (+/- 0.18, SEM), 0.57% of the mean value found in serum (360 microg/ml). This proportion was comparable to that of serum albumin (0.63% of serum value) but less than the proportion of C3 in milk (2.71%). Nevertheless, fB was apparently not a limiting factor for the functioning of the alternative pathway, since addition of purified fB to normal milk did not improve C3 deposition. In serum, mild heat-treatment (56 degrees C for 3 min or 50 degrees C for 45 min) blocked the alternative pathway and destroyed fB, as shown by loss of antigenicity in ELISA. In milk, mild heat-treatment did not abrogate C3 deposition, and fB was protected, retaining its functionality and antigenicity. Heating at 56 degrees C for at least 45 min was necessary to completely inhibit C3 deposition in normal milk.

Decreased number and bactericidal activity against Staphylococcus aureus of the resident cells in milk of dairy cows during early lactation

Phagocytic and bactericidal activity of polymorphonuclear neutrophil leukocytes (PMN) isolated from blood and milk, against Staphylococcus aureus, was compared between groups of six healthy dairy cows in early, mid- and late lactation using a bacteriological assay. PMN were isolated from blood with a high degree of purity, but the cells isolated from milk contained variable amounts of macrophages (Mphi) and lymphocytes (L). The results were therefore calculated using the percentage PMN in order to evaluate phagocytosis and killing by PMN only. Blood PMN phagocytosed 82% Staph. aureus and milk PMN 43% on average and there was no significant difference between the different stages of lactation. The bactericidal activity of blood PMN against Staph. aureus was 36+/-8% in early lactation (significantly different from mid lactation, P < 0.05), 64+/-10% in mid lactation and 53+/-6% in late lactation. Milk PMN killed only 6+/-3% Staph. aureus in early lactation (significantly different from mid lactation, P < 0.01), 27+/-3% in mid lactation and 20+/-9% Staph. aureus in late lactation. The ratio of the bactericidal activity of milk to blood PMN was 0.08, 0.43 and 0.22 in early, mid- and late lactation, respectively. In addition to the decreased function. the number of cells in milk (somatic cell count, SCC) was also 60% lower in early lactation than in mid lactation cows (P < 0.01). Our results suggest an impairment of blood and milk-resident PMN bactericidal activity against Staph. aureus and a decreased number of milk-resident PMN in dairy cows at the onset of lactation.

Cell subpopulations and cytokine expression in cow milk in response to chronic Staphylococcus aureus infection

Staphylococcus aureus is a major pathogen in bovine intramammary infections of subclinical and chronic nature. Persistent infection with S. aureus has been postulated to be associated with an impaired immune response. This study was designed to define changes in peripheral blood and milk cell subpopulations during chronic S. aureus infection. The expression of specific antigens on the surface of lymphocytes and neutrophils was studied by flow cytometry. Cytokines and cytokine transcripts elaborated by the milk-derived cells were also investigated, using ELISA and reverse transcription polymerase chain reaction, respectively. The results indicated that cell subpopulations in blood from infected cows were not modified. In contrast, changes occurred in infected milk: neutrophils were the main cell population, but they were not in a highly activated state; the CD8+ T-lymphocytes were mainly recruited compared with the CD4+ T-lymphocytes, suggesting that CD8+ T-lymphocytes play an important role in chronic S. aureus infection. Also, the proportion of the B-lymphocytes among the total lymphocyte population was increased, suggesting that a humoral response developed, and no change was observed in the gammadelta subset. No cytokine mRNA was found in milk cells from uninfected mammary glands. In contrast, interleukin (IL)-1alpha, IL-1beta, IL-6 and tumor necrosis factor alpha pro-inflammatory cytokine and IL-10 and IL-12 regulatory cytokine mRNA were synthesized in cells derived from infected mammary glands, whereas no IL-2 nor IL-4 mRNA were found. Therefore, cells present in milk during chronic S. aureus infection were activated, but did not reveal any polarization of the immune response.

Cells and cytokines in inflammatory secretions of bovine mammary gland

In response to invading bacteria, the mammary gland is protected by a variety of defence mechanisms, which can be separated into two distinct categories: innate immunity and specific immunity. Milk somatic cells consist of several cell types, including neutrophils, macrophages, lymphocytes and a smaller percentage of epithelial cells. In the healthy lactating mammary gland, macrophages are the predominant cell type whereas neutrophils are the major cell population during early inflammation. Following a bacteria invasion, neutrophil recruitment is elicited by inflammatory mediators that are produced in the infected gland by cells, possibly macrophages, activated by bacteria phagocytosis or responding to bacterial toxins or metabolites. Several cytokines, including interleukin- (IL-) 1 beta, IL-6, IL-8, tumour necrosis factor- (TNF-) alpha and interferon- (IFN-) gamma are known to be important to elicit the acute phase response and allow the accumulation of leukocytes at the site of infection. In addition to their role in early non-specific defences, macrophages also play a key role in the specific immune system, as antigen processing and presenting cells for the T cells. Few lymphocytes are found in milk of healthy glands where the predominant phenotype is CD8+ T cells. During the inflammatory reaction, T cells are recruited in milk and CD4+ cells become the predominant phenotype. The understanding of the specific and nonspecific immune mechanisms involved in the mammary gland defence against invading bacteria may lead to the development of new vaccines and to the use of cytokines to design immunomodulatory strategies for the control of bovine mastitis.

Influence of bispecific antibodies on the in vitro bactericidal activity of bovine neutrophils against Staphylococcus aureus

We conducted the following study to determine if bispecific antibodies enhance the bactericidal activity of bovine neutrophils. Bispecific antibodies were synthesized by chemically crosslinking bovine neutrophil monoclonal antibodies to Staphylococcus aureus 305 capsule polysaccharide monoclonal antibodies. The efficiency of chemically coupling monoclonal antibody monomers was approximately 50% for each bispecific antibody produced. Monoclonal antibodies against neutrophils enhanced the respiratory burst activity of neutrophils by 2.3- to 2.5-fold. To determine the influence of bispecific antibodies on neutrophil function, S. aureus 305 was preincubated with various concentrations of bispecific antibodies and neutrophils were then added to the opsonized bacteria at different bacteria to neutrophil ratios. The bactericidal activity of neutrophils was expressed as a percentage reduction in colony-forming units in test cultures compared with the number of colony-forming units in control test cultures that did not contain bispecific antibodies or neutrophils. The addition of bispecific antibodies to test cultures increased the bactericidal activity of neutrophils. A reduction in colony-forming units as a function of increasing the S. aureus 305 to neutrophils ratio was observed in both the absence and presence of bispecific antibodies. However, a greater reduction was observed in the presence of bispecific antibodies. Increasing concentrations of bispecific antibodies enhanced the bactericidal activity of neutrophils at a constant S. aureus 305 to neutrophil ratio of 1:500. The results indicate that bispecific antibodies that recognize both S. aureus 305 capsular polysaccharide and neutrophil antigens potentiate the bactericidal activity of neutrophils.

Kinetics of cells and cytokines during immune-mediated inflammation in the mammary gland of cows systemically immunized with Staphylococcus aureus alpha-toxin

OBJECTIVE

To examine changes in inflammatory mediators, lymphocyte subpopulations and neutrophil activation that occur during an immune-mediated recruitment of neutrophils in the mammary gland.

SUBJECTS

11 clinically healthy cows.

TREATMENT

5 cows received 2 subcutaneous injections of 30 microg of alpha-toxin of Staphylococcus aureus, two months apart. Three months after the last immunization, 5 microg of alpha-toxin were injected, via the teat end, in one randomly selected quarter of the 5 immunized cows and of the 6 unimmunized cows (control group).

METHODS

Blood and milk samples were collected at several times during 4 days post-challenge. Blood and milk cells were purified to be stained with specific mAbs and analysed by flow cytometry, or to be used for cytokine RT-PCR. Bovine serum albumin, haptoglobin, cytokines and C5a were also analysed in milk or plasma samples using radial immunodiffusion assay or ELISA.

RESULTS

Large amounts of cells (> 1 million/ml of milk) were recruited in the quarters of the immunized cows, whereas no recruitment occurred in the control group. In blood of immunized animals, haptoglobin was present and expression of surface adhesion molecules on neutrophils was modified whereas no change was observed concerning the lymphocyte subpopulations. On milk-derived neutrophils, the expression of CD11b and CD18 was upregulated compared to blood, in contrast to CD62L that was downregulated. The CD8+ cells were recruited as soon as 12 h post-challenge, in contrast to the CD4+ cells, 96 h post-challenge. No IL-1beta, TNF-alpha, IL-8 and C5a were detected using ELISA. mRNA of IL-1alpha, IL-1beta, IL-6, TNF-alpha, IL-8 and IL-12 were found in almost all the samples.

CONCLUSIONS

The immunization triggered an early and massive neutrophil recruitment from the blood into the milk compartment as well as the recruitment of a cytotoxic/suppressor lyphocyte population during the early acute phase response. These results could help to devise new vaccinal strategies to fight against staphylococcal mastitis.

Phagocytosis and killing of Staphylococcus aureus by bovine neutrophils after priming by tumor necrosis factor-alpha and the des-arginine derivative of C5a

OBJECTIVES

To evaluate effects of proinflammatory mediators on phagocytosis and killing of Staphylococcus aureus, the oxidative burst (OB), and expression of receptors for opsonins by bovine neutrophils.

SAMPLE POPULATION

Neutrophils from 10 cattle.

PROCEDURE

Neutrophils were primed with recombinant bovine tumor necrosis factor-alpha (TNF-alpha) or the des-arginine derivative of bovine C5a (C5a(desArg)) and mixed with S aureus. Phagocytosis and OB were measured by use of flow cytometry. Rate of phagocytosis and intracellular killing were evaluated. Expression of receptors for immunoglobulins and the C3bi fragment of complement were estimated by use of flow cytometry.

RESULTS

Priming of neutrophils by TNF-alpha improved phagocytosis of S aureus with a concentration-dependent effect. Phagocytosis of preopsonized washed bacteria was increased by activation of neutrophils with C5a(desArg). Phagocytosis was optimal when neutrophils primed with TNF-alpha were activated with C5a(desArg). The OB of phagocytizing neutrophils was highest when TNF-alpha and C5a(desArg) were used in combination. Bactericidal activity of neutrophils was stimulated by priming with TNF-alpha or C5a(desArg). Binding of bovine IgM or IgG2 to bovine neutrophils was not stimulated byTNF-alpha, C5a(desArg), or both, and aggregated IgG1 did not bind to neutrophils regardless of their activation state. Both TNF-alpha and C5a(desArg) increased expression of beta2 integrins (CD18), with the highest expression when they were used in combination.

CONCLUSIONS AND CLINICAL RELEVANCE

The mediators TNF-alpha and C5a(desArg) stimulated phagocytic killing by neutrophils and potentiated each other when used at suboptimal concentrations. Bovine neutrophils have enhanced bactericidal activities at inflammatory sites when TNF-alpha, C5a(desArg), or both are produced locally.

Generation of complement fragment C5a in milk is variable among cows

The appearance of chemotactic fragments of complement at sites of infection is an important component of innate immunity. The contribution of C5a, the most biologically active complement fragment, to the recruitment of phagocytes in milk is not well defined, in particular the amount of C5a that is released in normal milk before inflammation. The generation of C5a in normal milk upon activation of complement by invading bacteria depends on the amount of available C5 and on the activity of the C3/C5-convertase of the alternative pathway. Concentrations of C5 were measured in one fore and one rear uninfected quarter of 19 Holstein cows. Values were consistent within cows, but widely dispersed among cows (0.19 to 1.94% blood concentration). C5 concentrations in milk were loosely related to concentrations in blood. By comparison, the range of milk concentrations of C3 (1.4 to 4.4%, mean 2.46 +/- 0.63% of blood concentration) was narrower. Two groups of six cows with high milk concentrations of C5 (cows H5: mean = 1.31%) and six cows with low milk concentrations of C5 (cow L5: mean = 0.21%) were constituted for further analysis of complement activation. There was a positive correlation between concentrations in milk of BSA and C5, but not between concentrations of BSA and C3. The activities of the C3- and C5-convertases were assessed through the deposition on complement-activating bacteria (Streptococcus agalactiae) of C3 and C5 fragments, respectively. The deposition of C3 was 1.7-fold higher, and the deposition of C5 was 2.75-fold higher in milk from H5 cows than in milk of L5 cows. Higher concentrations of C5 and better functioning of C5-convertase were mirrored by a much higher concentration of C5a in milk from H5 cows (12.30 ng/ml) than in milk of L5 cows (0.76 ng/ml) after activation of complement with zymosan. These results indicate that cows differed widely in their capacity to generate C5a in milk before inflammation, and that milk C5 concentrations were a primary limiting factor for C5a generation. Cows with the lowest milk concentrations of C5 are likely unable to use the complement system for the initial recruitment of leukocytes.

Differential induction of complement fragment C5a and inflammatory cytokines during intramammary infections with Escherichia coli and Staphylococcus aureus

The prompt recruitment of neutrophils to the site of infection is essential for the defense of the bovine mammary gland against invading pathogens and is determinant for the outcome of the infection. Escherichia coli is known to induce clinical mastitis, characterized by an intense neutrophil recruitment leading to the eradication of the bacteria, whereas Staphylococcus aureus induces subclinical mastitis accompanied by a moderate neutrophil recruitment and the establishment of chronic mastitis. To elicit the neutrophil recruitment into the udder, inflammatory mediators must be produced after recognition of the invading pathogen. To our knowledge, those mediators have never been studied during S. aureus mastitis, although understanding of the neutrophil recruitment mechanisms could allow a better understanding of the differences in the pathogeneses elicited by E. coli and S. aureus. Therefore, we studied, at several time points, the accumulation of neutrophils and the presence of the chemoattractant complement fragment C5a and of the cytokines interleukin-1beta (IL-1beta), tumor necrosis factor alpha, and IL-8 in milk after inoculation of E. coli or S. aureus in lactating bovine udders. The low levels of C5a and the absence of cytokines in milk from S. aureus-infected cows, compared to the high levels found in milk from E. coli-infected animals, mirror the differences in the severities of the two inflammatory reactions. The cytokine deficit in milk after S. aureus inoculation in the lactating bovine mammary gland could contribute to the establishment of chronic mastitis. This result could help in the design of preventive or curative strategies against chronic mastitis.

Quantification of C5a/C5a(desArg) in bovine plasma, serum and milk

Complement activation generates two potent inflammatory mediators from C5, C5a and its derivative C5a(desArg), which results from the removal of the C-terminal arginine by ubiquitous carboxypeptidases. In this paper we describe the purification of milligram amounts of bovine C5a(desArg) by a simplified procedure, and the preparation of mouse monoclonal antibodies (MAbs) to C5a/C5a(desArg) which do not recognize native C5. A MAb was used to develop a sandwich ELISA which made it possible to quantify levels of C5a/C5adesArg in bovine biological fluids. Small amounts (means +/- SEM) of C5a/C5a(desArg) were found in EDTA-plasma (0.58 +/- 0.06 ng.mL-1). The anticoagulant EDTA was more efficient than citrate or heparin in inhibiting in vitro activation of the complement system. Complement activation occurred during coagulation since the baseline concentration of C5a/C5a(desArg) (15.4 +/- 4.1 ng.mL-1) was higher than in plasma. Zymosan, a potent activator of the complement cascade, was used to generate C5a/C5a(desArg). The time-course of the reaction and the dose-effect of zymosan were investigated. Optimal conditions were incubation at 39 degrees C for 1 or 2 h with 2 mg of zymosan per mL of serum. The maximal concentration of C5a/C5a desArg attained in zymosan-activated serum was 4.28 +/- 0.14 micrograms.mL-1. Normal milk (from healthy, uninflamed mammary glands) contained on average 0.12 ng of C5a/C5a(desArg).mL-1 (range 0.02-0.19 ng.mL-1). The maximal amount of C5a/C5a(desArg) which was generated in milk with zymosan was 1.1 ng.mL-1 (range 0.68-2.17 ng.mL-1). In milk from quarters with subclinical infections by coagulase-negative staphylococci, values were 0.18 ng.mL-1 and 2.37 ng.mL-1 for spontaneous and zymosan-generated C5a/C5a(desArg) concentrations, respectively. In milk from Escherichia coli endotoxin-induced mastitis, C5a/C5a(desArg) concentrations (means of four cows) before and after zymosan activation reached 6.5 ng.mL-1 and 55 ng.mL-1, respectively. These results indicate that a C5-convertase can operate in normal milk, that only minute amounts of C5a/C5a(desArg) can be generated (less than 1/1,000 of plasma potential), but that much higher concentrations are reached in milk during endotoxin-induced inflammation. The ELISA made it possible to determine normal ranges of C5a/C5a(desArg) in bovine blood plasma and in milk, and is a valuable tool to define the variations of its concentrations in exudates during inflammatory reactions.

Immune recruitment and bactericidal activity of neutrophils in milk of cows vaccinated with staphylococcal alpha-toxin

The ability of Staphylococcus aureus alpha-toxin to recruit neutrophils in the milk of vaccinated cows and the bactericidal efficiency of these neutrophils were evaluated. Six lactating Holstein cows that were free of intramammary infection received systemic immunization by subcutaneous injection of Freund's incomplete adjuvant with alpha-toxin (n = 2), alpha-toxin mixed with type 5 capsular polysaccharide (n = 2), or a conjugate of these two antigens (n = 2). Controls (n = 4) and vaccinated cows (n = 6) received intramammary infusions of alpha-toxin. No increase in somatic cell count was recorded in quarter milk samples from unimmunized cows; however, 10 micrograms of alpha-toxin induced a local inflammatory reaction in vaccinated cows that was characterized by early and massive cellular recruitment into the mammary gland. More than 90% of the recruited cells were neutrophils. The speed and magnitude of the cellular recruitment were dose-dependent; the threshold dose was 0.6 microgram. Milk samples showed significant bactericidal activity against the type 5 S. aureus strain, regardless of the vaccine used, and showed a decrease in bacterial count of about 2 log10 from the initial inoculum. The best efficiency was recorded during the early phase of cellular recruitment with concomitant activation of blood-derived neutrophils. This study demonstrates that a bacterial virulence factor, alpha-toxin, is able to induce immune recruitment of neutrophils for efficient bactericidal activity in milk when cows are immunized with alpha-toxin that is used either as a nonconjugate vaccinate or as a carrier protein in a conjugate vaccine. The study also suggests that neutrophils that are recruited from blood are activated during inflammation in response to specific antigens.

Complement fragment C5a and inflammatory cytokines in neutrophil recruitment during intramammary infection with Escherichia coli

Generation of inflammatory mediators and leukocyte recruitment to infection at an epithelial surface were studied during Escherichia coli-induced mastitis. One uninfected gland of each of eight midlactation cows was challenged with only 30 CFU of E. coli McDonald strain 487, a serum-resistant isolate from a cow with mastitis. Bacteria grew logarithmically during the first 10 to 12 h after challenge, reaching concentrations of more than 10(5) CFU/ml with no detectable host response during this time. An intense inflammatory reaction began approximately 12 h after the challenge and was characterized by a breakdown in the blood-milk permeability barrier followed by pyrexia and a pronounced leukocytic influx. Coincident with the onset of mammary inflammation was the appearance of neutrophil chemotactic activity in the milk from infected glands. Factors able to upregulate CD18 expression on peripheral blood neutrophils also appeared in milk at this time. The lack of appearance of chemotactic and CD18-upregulating activities until 12 h after challenge indicated that delays in neutrophil recruitment resulted from an initial lack of bacterial recognition and inflammatory mediator production. Production of complement fragment C5a, tumor necrosis factor, and interleukin-1 (IL-1) occurred earlier than production of IL-6 or IL-8. The early and intense production of C5a indicates that this chemoattractant may be more important than IL-8 during the initial recruitment and activation of neutrophils to a developing E. coli infection.

Evaluation of selected antibiotic residue screening tests for milk from individual goats

Because somatic cell counts (SCC) of caprine milk are higher than SCC of bovine milk, the performance of antibiotic residue tests for screening bovine milk was investigated for caprine milk. Eighty-five does that were free of antibiotic usage for at least 30 d and that were free of clinical mastitis were sampled at three milkings during a 37-d period. At each sampling, foremilk was collected for bacteriological analysis, and composite bucket milk samples were collected for antibiotic testing and SCC. Day of lactation, parity, 305-d mature equivalent milk yield, and SCC averaged 221 d (57 to 577 d), 2.3 lactations (one to nine lactations), 1160 kg (623 to 1750 kg), and 2.2 x 10(6)/ml (0.3 to 30.7 x 10(6)/ml), respectively. The mean Dairy Herd Improvement Association test day milk yield for the month of sample collection was 3 kg (1.4 to 6.4 kg). Intramammary infections were present in 54% of the goats and in 36% of the udder halves. Assays included positive (5 and 10 ppb of penicillin-G and 50 ppb of ceftiofur) and negative controls that had been prepared in caprine milk and controls supplied by the manufacturers. One false-negative outcome and one false-positive outcome were recorded. For one sampling day, a positive linear relationship existed between SCC and the results of one test, and a quadratic relationship existed between SCC and the results of another test. The antibiotic residue screening tests for milk from individual goats adequately identified milk that was free of antibiotic. These tests are therefore recommended for use with caprine milk.

Heterogeneity of cell-associated CP5 expression on Staphylococcus aureus strains demonstrated by flow cytometry

It was reported previously that two capsular polysaccharides, types 5 and 8 (CP5 and CP8), account for 70 to 80% of Staphylococcus aureus strains isolated from human and animal sources. The capsular material has been shown to play a part in virulence and in resistance to phagocytosis. With a view to investigating the role that CP plays in pathogenicity or protection, relative measurement of cell-associated CP is desirable. Flow cytometry, which permits the analysis of individual bacteria, was used to that end. Thirty isolates expressing CP5, of human (n = 7) and animal (cow, n = 11; goat, n = 3; swine, n = 3; hen, n = 3; and rabbit, n = 3) origin, were cultivated on either brain heart infusion agar (BHI) or modified medium 110 (mod 110) agar. Staphylococci were incubated with a mouse anti-CP5 monoclonal antibody (an immunoglobulin M, which does not react with staphylococcal protein A) and then stained with a fluorescein-labeled anti-murine antibody. The bacteria were washed, sonicated, and analyzed by flow cytometry. Except for three isolates, the expression of cell-bound CP5 was higher when bacteria were cultivated on mod 110 than when they were cultivated on BHI. We found a wide intraisolate phenotypic heterogeneity in surface-exposed CP5 in many strains, which appeared as mixtures of stained and unstained bacteria. Four main patterns could be distinguished on the basis of the distribution of the fluorescence of individual bacteria within the strain population as a function of growth medium. Great variations in both percentages of stained bacteria and fluorescence intensity were recorded among strains regardless of their origin. Flow cytometry analysis provided information on both the relative amounts and the distribution patterns of the surface expression of CP. This information is potentially useful for the evaluation of the part played by the capsule in the interaction of bacteria with host cells or for the study of the activities of antibodies to this target antigen, such as opsonization or prevention of adherence.

Sensitization of the bovine mammary gland to Escherichia coli endotoxin

The effect of repeated infusions of Escherichia coli endotoxin on the acute phase response in the bovine mammary gland was assessed through the concentrations of tumor necrosis factor alpha (TNF-alpha) in milk. Four clinically normal lactating cows received two intramammary infusions of E coli endotoxin (33 micrograms) 24 h apart in the same mammary quarter. Along with the second infusion, the cows received one dose of endotoxin in the contralateral quarter. Milk was collected at varying intervals before and after infusion and TNF-alpha concentrations were determined by ELISA. Following the first infusion at 0 h, the mean concentrations of TNF-alpha augmented from undetectable concentrations to a maximum of 0.4 ng/mL at 4 h and declined to below 0.04 ng/mL at 24 h, the time of the second infusion. In the quarters challenged twice, the increase in TNF-alpha concentrations was abrupt, culminating at 11.7 ng/mL 6 h later (at 30 h). The increases in TNF-alpha concentrations were similar in the contralateral quarters infused once. TNF-alpha concentrations in the control, uninfused quarters of infused cows remained undetectable (< 0.04 ng/mL). Despite the low TNF-alpha response following the first infusion, mean somatic cell counts increased markedly, being only slightly lower than after the second infusion (10(7)/mL and 5 x 10(7)/mL at 8 h and 32 h, respectively) in the quarters challenged twice. After the first infusion, none of the cows developed fever, but following the second infusion, rectal temperature increased markedly, culminating 6 h after the second infusion. These results show that an infusion in one quarter of an amount of endotoxin sufficient to induce a pronounced cell recruitment but insufficient to induce a marked TNF-alpha secretion following the first infusion sensitized not only that quarter but also the contralateral one to a second infusion with the endotoxin. It is thus possible that sensitization of the whole udder follows a first contact with a moderate dose of endotoxin in one quarter.

Cell culture system for studying bovine neutrophil diapedesis

Neutrophils are the major defense against bacterial infection in the bovine mammary gland. Neutrophils migrate from blood into the lumen of the gland in response to inflammatory stimuli. This study describes the development of a system of cell culture that can be used to study neutrophil diapedesis through secretory and ductal mammary epithelial barriers. The culture system consists of successive layers of collagen, fibroblasts, collagen, and a confluent monolayer of secretory or ductal epithelial cells layered on a porous membrane. Confluence was determined by electrical resistance and trypan blue diffusion. Neutrophil diapedesis occurred from the basal to the apical surface of the monolayers. Purified complement C5a, fetal bovine serum that had been activated by zymosan, and fetal bovine serum that had been activated by Escherichia coli induced neutrophil diapedesis. Neutrophil diapedesis was greater across ductal cell monolayers. Blood neutrophils from five cows differed in their ability to migrate through the multilayered culture system in response to C5a. Monoclonal antibodies to C5a blocked diapedesis induced by purified C5a but had no effect on diapedesis induced by fetal bovine serum that had been activated by zymosan or by fetal bovine serum that had been activated by E. coli endotoxin, indicating that factors other than C5a were chemotactic for neutrophils. Monomeric IgG2, immune complexes, and E. coli endotoxin did not induce neutrophil diapedesis.

Deposition of complement components on Streptococcus agalactiae in bovine milk in the absence of inflammation

Bovine milk is generally considered to be almost devoid of complement, on the basis of undetectable hemolytic activity, unless inflammation recruits plasma components. This study examines the deposition of complement components on a mastitis-causing isolate of Streptococcus agalactiae by enzyme-linked immunosorbent assay (ELISA). Neat milk from mid-lactating, uninflamed mammary glands (normal milk) effected marked C3 deposition on bacteria. Kinetic studies showed a protracted lag period (30 to 45 min) preceding C3 deposition, which required about 2 h to reach a maximum. Experiments with diluted serum suggested that this slow C3 deposition resulted mainly from the low concentration of certain components of complement in milk. Bacteria incubated in neat milk readily bound bovine conglutinin, indicating the presence of iC3b. Elution of covalently bound C3 fragments with hydroxylamine confirmed the deposition of C3b and iC3b on bacteria. Deposition of C4 on bacteria was not detected in neat milk, suggesting that C3 deposition did not result from the activation of the classical pathway. This was not the result of a lack of antibodies. However, C4 deposition could be obtained by adding purified bovine C1q to normal milk, and C3 deposition was accelerated, suggesting the participation of the classical pathway. The deposition of C1q on antibody-sensitized bacteria was impeded by milk compared with that of C1q diluted in phosphate-buffered saline. Concentrations of C1q in normal milk were very low, ranging from 150 to 250 ng/ml. Overall, these findings indicate that C1q was a limiting factor of the classical pathway in normal milk. The capacity of milk to deposit C3 fragments on mastitis-causing S. agalactiae prompts further studies to investigate its role in opsonophagocytosis.

Phenotypic variability of X-protein expression by mastitis-causing Streptococcus agalactiae of serotype NT/X and opsonic activities of specific antibodies

This study examined the role of antibodies against the X-protein, a surface-localized antigen frequently associated with streptococci causing mastitis in cattle, in the opsonization and phagocytosis of unencapsulated Streptococcus agalactiae. The analysis of various strains of serotype NT/X by flow cytometry, after labeling with a monoclonal antibody to X-protein, revealed that they consisted of a mixture of unstained and stained bacteria. Cloning of mother strains yielded clones of unstained bacteria but not homogeneous clones of stained bacteria. Analysis by ELISA of an unstained clone (4.1) derived from the reference NT/X strain 24/60 indicated that it expressed low amount of X-protein at its surface, about 25 times less than the stained clone 24/60 5.6. Colloidal gold immunolabeling showed the X-protein at the periphery of bacteria (of clone 5.6 and in lower amount of clone 4.1), at a distance from the cell wall. Bovine antibodies (essentially IgG) to X-protein behaved like the monoclonal antibody in the cytometric assay. They activated the classical pathway of complement as shown by the deposition of C1q and C4 on bacteria. Deposition of C4 also occurred on the low-surface-producing clone 4.1 in the presence of antibodies to X-protein, although less efficiently than on the high-surface-producing clone 5.6. When used alone, antibodies promoted the ingestion of bacteria and heat-inactivated immune serum promoted the chemiluminescence activity and the killing by polymorphonuclear cells. In conclusion, antibodies to X-protein induced the deposition of C3 by the classical pathway and were also able to stimulate opsonophagocytic killing of X-bearing S. agalactiae in the absence of deposited C3.

Activation of the classical pathway of complement by binding of bovine lactoferrin to unencapsulated Streptococcus agalactiae

The ability of lactoferrin (Lf) bound to Streptococcus agalactiae to interfere with the deposition of complement components on the bacterial surface was investigated by enzyme-linked immunosorbent assay (ELISA). By using a strain of S. agalactiae which activates the alternative pathway of complement in the absence of antibodies, it was found that pretreatment of bacteria with Lf shortened the lag phase preceding the deposition of C3 on bacteria. The kinetics of C3 deposition was comparable to that obtained by adding antibodies against S. agalactiae to agammaglobulinaemic precolostral calf serum (PCS) heated at 56 degrees for 3 min to inactivate the alternative pathway. Accelerated C3 deposition did not occur in the absence of Ca2+ ions. Deposition of C4 on bacteria occurred only when either antibodies or Lf were added to PCS. These results demonstrate that the interaction of lactoferrin with bacteria activated the classical pathway of complement in the absence of antibodies. The binding of purified C1q to bacteria was promoted in a dose-dependent manner by Lf, suggesting that recruitment of classical pathway of complement resulted from the interaction of C1q with Lf adsorbed to the bacterial surface. Phagocytosis of bacteria opsonized with heated PCS (at 56 degrees for 3 min) and Lf was comparable to that occurring in the presence of heated PCS and antibodies. In conclusion, Lf was able to substitute for antibodies in order to activate the classical pathway of complement and to opsonize unencapsulated S. agalactiae efficiently.

Binding of bovine fibronectin to mastitis-causing Streptococcus agalactiae induces adherence to solid substrate but not phagocytosis by polymorphonuclear cells

Streptococcus agalactiae is frequently associated with mastitis in cattle, and fibronectin is a host protein which interferes with infection, particularly at mucosal sites. The binding of bovine fibronectin to S. agalactiae was investigated by enzyme-linked immunosorbent assay (ELISA). Binding was time-dependent and dose-dependent. Most of the strains tested showed low ELISA activity, but some strains (six out of 17) had much higher activity. The highest-binding strains of S. agalactiae were able to adhere to bovine fibronectin-coated polystyrene. Adherence was inhibited by arginine or gelatin, but was slightly favored by soluble fibronectin. Fibronectin did not contribute to the opsonization (deposition of complement C3) and phagocytosis of the strain which bound the highest amount of fibronectin, even when polymorphonuclear cells were activated with serum-derived chemotaxin (C5a). These data suggest that fibronectin might promote tissue adherence but not phagocytosis of S. agalactiae in the mastitis process.

Binding of bovine lactoferrin to Streptococcus agalactiae

Bovine lactoferrin is an iron-binding protein present in mammary gland secretions. The exposure of Streptococcus agalactiae to bovine lactoferrin resulted in the binding of this protein to all the 12 strains of bovine origin tested, and also, although to a lesser degree, to the five tested strains of human origin. The interaction of lactoferrin with one high-binding bovine strain (24/60, the prototype NT/X strain) was studied. Binding was time-dependent, dose-dependent, and saturable. The binding of lactoferrin was slightly affected by cultivation conditions, and appeared to be heat-stable. The binding of biotinylated lactoferrin was inhibited by unlabelled lactoferrin but not by bovine serum albumin.

Opsonization of Streptococcus agalactiae of bovine origin by complement and antibodies against group B polysaccharide

The contribution of bovine complement and antibodies (Ab) against the group B polysaccharidic antigen (GBA) to the opsonization of Streptococcus agalactiae isolated from bovine mastitis cases was investigated by using affinity-purified Ab. GBA-specific Ab were not opsonic by themselves, but in the presence of complement (precolostral calf serum) with an opsonization time of 15 min, they exhibited a dose-dependent opsonic activity in a polymorphonuclear leukocyte chemiluminescence assay. Kinetic studies of the deposition of complement component C3 on protein X-bearing nontypeable (NT/X) strains with an enzyme-linked immunosorbent assay showed that C3 was deposited on bacteria in the absence of Ab but that GBA-specific Ab markedly accelerated the process by reducing the lag phase, which extended up to 15 min when Ab were absent. In the absence of Ab, C3 deposition was inhibited by 5 mM salicylaldoxime or heat treatment at 56 degrees C for 3 min and necessitated Mg2+ ions but not Ca2+ ions, suggesting that activation of complement was effected by the alternative pathway only. When GBA-specific Ab were added to complement, the inhibitory treatments lost much of their efficacy, suggesting that the classical pathway was recruited. Deposition of C3 on NT/X strains in the absence of Ab induced chemiluminescence and phagocytic killing. With the addition of GBA-specific Ab, the numbers of surviving bacteria were halved (P < 0.05) compared with killing in the presence of complement alone. It can be concluded that NT/X strains are activators of the alternative pathway of complement and that GBA-specific Ab reinforce the opsonic efficiency of serum by recruiting the classical pathway and slightly enhancing phagocytic killing.

Isotype antibody response in cows to Streptococcus agalactiae group B polysaccharide-ovalbumin conjugate

Adult dairy cows were immunized with group B antigen (GBA) of Streptococcus agalactiae or GBA coupled to ovalbumin, both emulsified in incomplete Freund adjuvant, and their sera were examined by an enzyme-linked immunosorbent assay measuring bovine immunoglobulin isotypes (immunoglobulin G1 [IgG1], IgG2, and IgM) specific for GBA. All of the cows possessed naturally acquired antibodies against GBA, which implied that primary antibody responses could not be studied. At the highest dose tested (200 micrograms), free GBA elicited a slight increase in antibody titers only in the IgM isotype, to which most of the naturally acquired antibodies to GBA belonged. A second administration of antigen was not more effective. The conjugate was able to induce a strong humoral response against GBA, particularly in the IgG1 and IgG2 subisotypes, and a second injection of the conjugate induced a doubling of the peak antibody titers. Therefore, conjugation of GBA to a protein carrier markedly improved the antibody response, which showed the main characteristics of T-cell dependency. The opsonic activity of serum against an unencapsulated strain of S. agalactiae was reinforced by the immunization with the conjugate.

Protein X of Streptococcus agalactiae induces opsonic antibodies in cows

Protein X of Streptococcus agalactiae is a surface protein frequently associated with strains isolated from cases of mastitis of dairy cows. By immunizing cows with purified protein X, we obtained an antibody response which was restricted to X-bearing strains of S. agalactiae in a whole-cell enzyme-linked immunosorbent assay. This response resulted in an increase in the opsonic activity of serum for strains bearing protein X, as assessed through the augmentation of the chemiluminescence response of phagocytosing polymorphonuclear cells and through an increased ingestion of bacteria, although the proportion of ingested bacteria which were killed (about 60%) remained unchanged. Protein X behaved as a target of opsonins and, as such, could be a protective antigen worth incorporating in a vaccine against S. agalactiae mastitis.

Purification of the protein X of Streptococcus agalactiae with a monoclonal antibody

The protein X of Steptococcus agalactiae is a surface antigen included in the typing scheme of group B streptococci (GBS). We have developed a monoclonal antibody to the protein X and used it to purify this antigen by affinity chromatography. Electrophoresis in polyacrylamide, and immunoblotting using the monoclonal antibody or a rabbit antiserum raised with the affinity purified protein X, revealed a major band in the region of 200 kDa and a smaller one at 100 kDa. The isolated protein X will make possible investigations of its potential role in virulence and protection.

The kinetics of inflammation and phagocytosis during bovine mastitis induced by Streptococcus agalactiae bearing the protein X

The protein X of Streptococcus agalactiae is a surface antigen borne by a high proportion of strains isolated from bovine mastitis. We have tested the capacity of two strains of X-bearing Streptococcus agalactiae to induce mastitis in dairy cows. The reference X-strain (411.07) produced an intramammary infection with local clinical signs in the three inoculated quarters. Another X-bearing strain (443.31) of bovine origin produced infection in all 11 quarters inoculated with only 25 or 85 colony-forming units. In naive cows, strain 433.31 induced less exudation of plasma into the milk, shedding of bacteria, macroscopic alteration, and a lower somatic cell count (SCC) than did the reference strain. Only one quarter spontaneously eliminated the infection before antibiotic treatment 9 days after inoculation. The serum of all the cows contained naturally acquired or induced antibodies to the challenge strain (443.31) and possessed opsonic activity. Before inflammation occurred, the milk was almost devoid of antibody or opsonic activities. The early phase of infection was characterized by rapid multiplication of streptococci in the milk, followed by a sharp drop in bacterial counts concomitant with the onset of inflammation. Three cows immunized with protein X displayed higher SCC and bactericidal activity in milk from the inoculated quarter at the onset of inflammation than non-immunized cows. Two of the three immunized cows underwent an early and transient febrile episode and eliminated the infection.

Effect of milk or colostrum on phagocytosis of glass- or plastic-adherent Streptococcus agalactiae by bovine granulocytes

In the presence of milk, bovine polymorphonuclear cells (PMN) assumed a polarized shape, a feature of motile cells, and their adherence to plastic was augmented. Milk enhanced the phagocytosis of glass- or plastic-adherent Streptococcus agalactiae. In contrast, PMN were not stimulated by colostrum.

Phagocytosis of mastitis isolates of Staphylococcus aureus and expression of type 5 capsular polysaccharide are influenced by growth in the presence of milk

Phagocytosis by bovine polymorphonuclear granulocytes of seven capsular polysaccharide type 5 Staphylococcus aureus strains isolated from mastitis [corrected] was investigated by means of luminol-dependent chemiluminescence. Bacteria were grown on four different agar media (brain heart infusion, Columbia broth, modified staphylococcus medium 110, and skim milk) and were opsonized by normal bovine serum. When compared to growth on brain heart infusion agar, Columbia agar, and modified staphylococcus medium 110 agar, growth on skim milk agar rendered five of the strains more resistant to opsonization. The other two strains were resistant in all culture media used. Short periods of incubation in milk after growth on brain heart infusion agar did not augment resistance to phagocytosis, indicating that mere adsorption of milk components on bacteria was not responsible. The variability of the chemiluminescence response of polymorphonuclear leukocytes was pronounced among strains with each growth medium except milk. Growth on modified staphylococcus medium 110 and on milk agar favored the masking of teichoic acid, as shown by inagglutinability with rabbit antiserum. Interestingly, agglutination by a monoclonal antibody to capsular polysaccharide type 5 was optimal when bacteria were grown on skim milk agar. This suggests that capsular polysaccharide participated in the masking effect. These findings indicate that masking of the bacterial target of most of the naturally acquired opsonins present in normal bovine serum occurred when bacteria grew in the presence of milk, resulting in an increased resistance to phagocytosis by polymorphonuclear leukocytes.

Encapsulation of Staphylococcus aureus isolates from mastitic milk: relationship between capsular polysaccharide types 5 and 8 and colony morphology in serum-soft agar, clumping factor, teichoic acid, and protein A

A total of 193 Staphylococcus aureus isolates from bovine, caprine, and ovine mastitis producing type 5 or 8 capsular polysaccharides were investigated for colony morphology in serum-soft agar and agglutinability by an anti-teichoic acid serum, after cultivation in modified staphylococcus medium no. 110. Also, 40 of these strains were cultivated in brain heart infusion and submitted to clumping factor and protein A detection tests. Considering capsular serotyping as a reference method, diffuse growth in serum-soft agar and inagglutinability by anti-teichoic acid serum identified, respectively, 57.5 and 45% of encapsulated strains cultivated in brain heart infusion and 85.5 and 77.2% of those cultivated in modified staphylococcus medium 110. Consequently, these indirect techniques underestimated encapsulation and were greatly influenced by culture conditions. Whatever the medium used, diffuse colony morphology in serum-soft agar was generally characterized by a masking of teichoic acid and protein A. By contrast, these surface antigens were detected in association with compact morphology; the presence of a thin or discontinuous capsular material could explain this result. Moreover, the masking of teichoic acid and the removal of capsular polysaccharide by washing in saline suggest that type 8 capsular polysaccharide is more abundant and labile than type 5.

The contribution of mammary infections by coagulase-negative staphylococci to the herd bulk milk somatic cell count

Quarter foremilk samples were taken at 2-3 weekly intervals for several years in an experimental herd comprising about 45 cows. The samples were submitted to bacteriological analysis and somatic cell counting. The most prevalent quarter infections from 1982 to 1988 were by coagulase-negative staphylococci (15-20% of all the quarters sampled). Most of these (75.6%) persisted until drying-off. Dry cow therapy eliminated 86.5% of these infections. Comparison of udder quarters within cows, involving 775 samples from pairs of non-infected quarters and quarters infected by coagulase-negative staphylococci, yielded geometric means of somatic cell counts of 210,000 and 420,000 cells/ml, respectively. The correlation (r = 0.87) between the herd bulk milk somatic cell count (SCC) and its estimation from the quarter milk somatic cell count performed on the same day allowed us to evaluate the contribution of the different categories of quarters, according to their infection status, to the herd bulk milk SCC. Quarters infected by a major pathogen (8.5% of samples) gave rise to 46.6% of the total number of cells, while quarters infected by coagulase-negative staphylococci (17.8% of samples) gave rise to 18.1%. Although coagulase-negative staphylococci represented only a secondary source of somatic cells as compared to major pathogens, they were not a negligible source considering the threshold of 300,000 somatic cells advocated for herd milk of good quality.

Assessment of phagocytosis of plastic adherent group B streptococci by ELISA quenching

An ELISA was devised to quantitate the number of group B streptococci (GBS) adherent to flat-bottomed 96-well microtiter plates. Ingestion of GBS by bovine polymorphonuclears (PMN) led to a decrease in ELISA values. This ELISA quenching proved to be proportional to phagocytosis. The method is suitable for kinetic studies of phagocytosis using glutaraldehyde to block the uptake of bacteria. The ELISA quenching test is applicable to a large number of samples and permits the use of the semi-automated equipment developed for ELISA.

Ingestion and killing of Streptococcus agalactiae by bovine granulocytes in the presence of natural opsonins

An enzyme-linked immunosorbent assay (ELISA) demonstrated the presence of naturally acquired antibodies against Streptococcus agalactiae in normal bovine serum (NBS). In milk wheys, ELISA values were much lower than in sera. Pre-colostral calf serum (PCS) was shown to lack antibodies to type II and III S. agalactiae. The opsonic requirements of 10 human and 10 bovine strains were investigated by evaluating the phagocytosis-induced reduction of the incorporation of radiolabeled thymidine by streptococci. Antibodies present in NBS were required for the efficient ingestion of both human and bovine isolates type II by bovine granulocytes. Three out of five type III bovine isolates were opsonized in the absence of specific antibodies (opsonization by PCS) and type II and III bovine isolates did not require complement opsonization. By contrast, inactivation of complement reduced phagocytosis of human isolates and only one type III strain of human origin was opsonized by PCS. These findings suggest that human isolates had higher opsonic requirements. The phagocytic killing of 6 type III strains (5 mastitis isolates and the reference typing strain) was investigated. Opsonization by normal serum enabled bovine blood granulocytes to ingest and kill S. agalactiae. Nevertheless, greater than or equal to 35% of bacteria remained viable at the end of the phagocytosis incubation in 10% NBS. Heat treatment of serum decreased the efficacy of killing for only 3 of the 6 tested strains. An IgG2 fraction of normal adult bovine serum promoted active ingestion, which was still increased in the presence of PCS. Normal wheys displayed large variations in their ability to promote ingestion of S. agalactiae by blood granulocytes. The promoting effect was systematically less than that of serum from the same cow, and this can be related to the lower ELISA values found in wheys.

Adherence, spreading, and locomotion of bovine polymorphs: effect of proteins and metabolic inhibitors

Adherence of bovine polymorphonuclear cells (PMN) on plastic, glass, and nylon wool fibers was assayed in the presence or in the absence of proteins and metabolic inhibitors. PMN adhered strongly and flattened on naked surfaces (without proteins). This process was active (did not occur at 5 degrees C), independent of divalent cations, and resisted the action of inhibitors except that of 10(-3) M iodoacetic acid, an inhibitor of glycolysis. A dose-dependent inhibitory effect was exerted on PMN adherence by fibrinogen and gelatin, whereas ovalbumin and human serum-albumin (HSA) inhibited only cell spreading. Bovine serum inhibited spreading and reduced attachment. In the presence of HSA, PMN adherence to plastic required the correct temperature (37 degrees C) and an intact glycolytic pathway and oxidative metabolism. PMN migration under agarose was reduced on naked plastic when compared to plastic pre-coated with gelatin. Incorporation of gelatin or HSA in the agarose also permitted the cells to respond to serum chemoattractants, without stimulation of random locomotion. Incorporation of heated precolostral calf serum in agarose resulted in the highest response to serum chemoattractants but also in stimulated random locomotion. These results suggest that PMN adhered too strongly to naked surfaces to be able to respond well chemotactically, and that the proteins used in the migration test under agarose operated mainly through a reduction of cell-surface interactions.

Effect of naturally occurring intramammary infections by minor pathogens on new infections by major pathogens in cattle

New mammary infections were recorded in 3 dairy herds during a lactation period by bacteriologic examination of milk samples at 3-week intervals. Influences of the infection status of quarters at the time of new infection and of microorganisms responsible for bacterial invasion were analyzed. The new infection rate in uninfected quarters was about 3 times the rate in quarters already harboring bacterial considered minor pathogens (coagulase-negative staphylococci and Corynebacterium bovis) or major pathogens (Staphylococcus aureus, streptococci). The frequency of new infections with major pathogens was almost halved by preexisting infections with minor pathogens (P = 0.05), mainly because of coagulase-negative staphylococci (P = 0.05) and, to a lesser extent, C bovis (P = 0.19). New infections by minor pathogens also were less frequent in quarters harboring a major pathogen (P less than 0.05), indicating that the competition or antagonism between mammary infections was a general phenomenon.