首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 405 毫秒
1.
Encapsulated strains of Escherichia coli were found to be more resistant to phagocytosis and killing by bovine neutrophils; requiring in the order of 100 times more serum opsonins than non-encapsulated strains. Mid-lactation pooled whey from cows with no history of mastitis was opsonic for non-encapsulated strains, but had no effect on encapsulated organisms. In contrast, early lactation pooled whey (5-10 days post-partum) was opsonic for all strains of E. coli. It is concluded that since early lactation milk contains sufficient opsonins, severe E. coli mastitis at this stage of lactation is not due to opsonic deficiency.  相似文献   

2.
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.  相似文献   

3.
The respiratory burst activity of bovine polymorphonuclear (PMN) cells in response to milk whey- and TSB-grown S. aureus strains isolated from bovine mastitis was studied in whole blood chemiluminescence (CL) and in a CL system with purified bovine neutrophils. In both cases milk whey-grown S. aureus strains elicited significantly less CL than homologous strains grown in TSB. Ingestion of milk whey-grown S. aureus strains by bovine neutrophils was also considerably lower than that of the corresponding homologous organisms grown in TSB. Binding of complement factor C3 to serum-opsonized milk whey-grown S. aureus strains was lower compared with TSB-grown homologous organisms. Moreover, 5 of 6 S. aureus strains grown in milk whey were significantly more resistant to in vivo clearance from the peritoneal cavity of mice compared with homologous bacteria grown in TSB. S. aureus strains grown in TSB exhibited hydrophobic surface properties, whereas homologous strains grown in milk whey were hydrophilic.  相似文献   

4.
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.  相似文献   

5.
Factors that influenced the in vitro bactericidal activity of bovine neutrophils against Actinomyces pyogenes were investigated. Neutrophils and serum from 2 clinically normal donor cows were incubated with bacteria for 2 hours. To determine bactericidal activity, colony-forming units were counted after a 48-hour incubation on blood agar plates. Microscopic examination indicated that in the presence of serum, bacteria were cell associated after incubation, whereas when serum was replaced by medium, bacteria were not cell associated. Bactericidal activity of neutrophils was similar whether the sera were heat-treated at 56 C for 30 minutes or were not heated. Heating the serum at 65 C for 30 minutes significantly (P less than 0.001) reduced bactericidal activity. Bactericidal activity decreased (P less than 0.001) as serum concentration (less than 10%) decreased. More than 80% of the bacteria were killed within the 40 minutes of incubation. The opsonizing capacity of serum varied significantly (P less than 0.01) among 12 cows. Similarly, neutrophil bactericidal activity (by cow) was affected significantly (P less than 0.001). Preincubation of serum with A pyogenes significantly (P less than 0.001) reduced the opsonizing ability of the serum. Culture filtrate of A pyogenes was not chemotactic for neutrophils in vitro.  相似文献   

6.
The role of indirect binding of host proteins through glycosaminoglycans (GAGs) on adherence and internalization of Streptococcus uberis to bovine mammary epithelial cells was evaluated. Preincubation of S. uberis with GAGs followed by incubation with fetal bovine serum (FBS), bovine milk or milk proteins resulted in greater adherence to and internalization of S. uberis into mammary epithelial cells than observed in untreated controls. Highest values were detected, when final incubation was done with milk. Greater adherence to and internalization into mammary epithelial cells were observed when heparin sulfate (HEP) and milk were used compared with any other GAG and FBS. When individual milk proteins were used, greatest adherence and internalization were observed when S. uberis strains were pretreated with HEP followed by treatment with beta-casein. The findings of this study illustrate a pathogenic strategy of S. uberis that may occur during the very early stages of infection.  相似文献   

7.
Following growth in a chemically defined medium (CDM), five strains of Streptococcus uberis were tested for their ability to survive killing by bovine neutrophils. Strains 0140J, ST10, EF20 and C221 were easily killed, whereas strain C197C was highly resistant. The ability of strain 0140J to resist phagocytosis and killing was increased by supplementation of the growth medium with milk whey, casaminoacids, casein, or, to a lesser extent, bovine serum. Supplementation of the growth medium with yeast extract or bovine serum albumin did not affect the resistance of this strain. Following growth in CDM supplemented with casein, strains ST10 and C221, like strain 0140J, were significantly more resistant to killing by neutrophils. The resistance of strains EF20 and C197C was unaffected by the addition of casein to the medium; strain EF20 remained susceptible and strain C197C highly resistant to killing. The effect of supplementing the growth media with components other than casein was only studied for strain 0140J. Decapsulation of strains C197C, ST10 and 0140J, grown in CDM + casein, with type-X hyaluronidase did not significantly affect their ability to survive in the presence of bovine neutrophils.  相似文献   

8.
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.  相似文献   

9.
Modulation of peripheral blood and mammary gland neutrophil function following in vitro exposure to recombinant bovine granulocyte-macrophage colony-stimulating factor (rBoGM-CSF) was studied. Bovine blood and mammary gland neutrophils were cultured for 9 h in media containing 0.005, 0.05 or 0.5 microgram/mL rBoGM-CSF. Neutrophils treated with rBoGM-CSF exhibited significantly more chemotactic and bactericidal activities and tended to produce more superoxide anion than control cells. The effects of rBoGM-CSF on bovine neutrophil populations appeared to be dose-dependent. The production of superoxide anion and the bactericidal activity of mammary gland neutrophils were consistently higher than blood neutrophils. Only moderate increases in lipopolysaccharide-induced mammary gland neutrophil functions were observed following incubation with rBoGM-CSF which suggests that there may be a threshold of immunomodulation for these prestimulated cells. It may be possible to augment the functional capacity of bovine neutrophil populations in vivo through the therapeutic application of rBoGM-CSF and consequently enhance resistance of dairy cattle to bacterial infections.  相似文献   

10.
The aim of this study was to evaluate the influence of age and plasma treatment on neutrophil phagocytosis, CD18 expression and serum opsonic capacity in foals in field settings. Microbial infections constitute a large threat in young foals and neutrophil functions are crucial for the defense. Blood samples were obtained from 13 foals at seven time points between the ages of 2 and 56 days and once from 16 adult horses. Six of the foals were treated with adult plasma at the age of 1 week. Neutrophil phagocytosis of yeast after various opsonizations and the expression of complement adhesion receptor CD18 were analysed by flow cytometry. Autologous serum opsonization resulted in 52+/-6.1% phagocytic neutrophils in 2-day-old foals (n = 12), a significantly lower rate than in adult horses (mean 84+/-3.1%; n = 16). In foals, yeast ingestion per neutrophil was also lower than in adults. Opsonic capacity increased with age (p < 0.05), reaching adult levels at 3-4 weeks. An increase in serum opsonic capacity followed plasma treatment (p < 0.05). The phagocytic capacity of foal neutrophils at the time-points studied was equal to or higher than that in the adults, when pooled adult horse serum or anti-yeast IgG was used as opsonin. In foals, serum IgG concentration was negatively correlated to serum opsonic capacity. CD18 receptor expression was higher in neutrophils from foals (<21 days old) than in those from adult horses (p < 0.05). The results indicate that foals are transiently deficient in serum opsonic capacity, which negatively affects their capacity for neutrophil phagocytosis. These changes in serum opsonins, unrelated to IgG, may be important factors in susceptibility to infections in foals.  相似文献   

11.
Leukocidin toxin from a bovine strain of Staphylococcus aureus was partially purified by ion exchange chromatography. An enzyme-linked immunosorbent assay was developed to quantitate antibodies specific for leukocidin in bovine milk. This was used to assay quarter samples from 88 cows in a S aureus-infected herd for antibody levels to the toxin. Milk samples from 65 cows with S aureus infections in at least one quarter produced a mean optical density of 1.054, whereas milk samples from 23 cows that were free of bacteria on cultural examination had a mean optical density of 0.584. There was a significant difference (P less than 0.001) in milk anti-leukocidin levels between these 2 groups. Evaluation of serum samples from 40 of these cows indicated that the milk anti-leukocidin concentrations were reflective of systemic anti-leukocidin values. The capability of 57 milk samples to neutralize the cytolytic effect of minimal amounts of leukocidin on bovine peripheral blood neutrophils was examined. Good correlation existed between the enzyme-linked immunosorbent assay antibody concentration and toxin-neutralizing capability of individual milk samples.  相似文献   

12.
Neutrophils are the first line of defense in a mammary gland infection. However, the process of neutrophil transmigration across a membrane and ingestion of fat and/or casein when incubated in milk have been shown to inhibit bacterial phagocytosis and oxidative burst functions. Recently, a killing mechanism has been described whereby stimulated neutrophils release nuclear and granule material in fibrous webs that physically trap and kill bacteria. We demonstrate that these neutrophil extracellular traps are also produced by bovine blood neutrophils stimulated with PMA/ionomycin. Importantly, neutrophil extracellular traps can be formed when neutrophils have been incubated for up to 6h in milk prior to stimulation. This contrasts milk's rapid inhibition of bacterial phagocytosis and oxidative burst functions in the neutrophil. Furthermore, stimulation of neutrophils with bacteria common to mammary gland infections leads to neutrophil extracellular traps being formed in milk. Some bacteria tested stimulated enhanced formation of neutrophil extracellular traps in milk compared to culture media. Therefore, being unaffected by incubation in milk may indicate an important role for neutrophil extracellular traps in defense against mastitis.  相似文献   

13.
Strains of Staphylococcus aureus were isolated from bovine mastitis, subcultured and maintained in the laboratory for up to 3 years. Encapsulation was assessed by production of a diffuse colony in serum-soft agar. Eight (4%) of 200 strains were encapsulated. Three rapid passages of the remaining 192 strains through either brain-heart infusion broth containing 30% serum or modified 110 medium retrieved the capsule in 75%, but this was rapidly lost after subculture on blood agar. The stimulation of capsule production was studied in 18 of these strains by addition of various components to the passaging medium. Heat-labile factors in serum, milk and mastitic milk enhanced capsule production while bovine serum albumin, an extract of polymorphonuclear leucocytes, NaCl and immunoglobulins had minimal effect. The results indicate that encapsulation is common in bovine staphylococci and while it is lost on subculture, may be retrieved under appropriate conditions.  相似文献   

14.
The cytotoxicity of Moraxella bovis whole cells and culture filtrates was studied, using 51Cr-labeled bovine and human blood neutrophils. The cytotoxicity of living M bovis was directly related to the concentration of bacteria in the neutrophil cultures, and was maximal at an approximate neutrophil to bacteria ratio of 1:10. Cytotoxicity was maximal by 30 minutes after living bacteria were added to the suspension of the 51Cr-labeled neutrophils. Expression of the cytotoxicity was dependent on the presence of Ca2+ in the media, and was independent of the presence of Mg2+. Cytotoxic activity was eliminated by inactivating M bovis in buffers containing formalin or sodium azide. Hemolytic and nonhemolytic isolates of M bovis were examined for cytotoxic activity. All 7 of the hemolytic isolates were cytotoxic for bovine neutrophils, but all 4 of the nonhemolytic isolates were devoid of cytotoxic activity. None of the 11 isolates were cytotoxic for human neutrophils. Sterile filtrates from 6-hour shaker cultures of a hemolytic M bovis isolate were cytotoxic for bovine neutrophils. Cytotoxicity of the filtrate was eliminated by heating, incubation with trypsin, or addition of EDTA to the media. Bacterial homogenates or sterile filtrates prepared from statistically incubated cultures of M bovis were not toxic for bovine neutrophils.  相似文献   

15.
The effects of Moraxella bovis on the morphologic features of purified bovine neutrophils and bovine corneal epithelial cells were examined, using transmission and scanning electron microscopy and light microscopy. Within 2 minutes after incubation of bovine neutrophils with living M bovis, electron microscopic cellular changes included vacuolation, swelling, and loss of microplicae. Most of the neutrophils were lysed by 10 minutes of incubation. Human neutrophils phagocytosed the M bovis and remained intact, even after 30 minutes of incubation with the bacteria. Living M bovis killed bovine corneal epithelial cells in vitro. Sterile filtrates prepared from 6-hour shaker cultures of M bovis also killed bovine corneal epithelial cells, but the cytotoxic activity was less than that produced by the living bacteria. Cellular changes were first observed in specimens collected 1 hour after corneal cell monolayers were inoculated with sterile culture filtrates. The changes in these cells included pit-like lesions on the cellular surface, cellular separation, and vacuolation.  相似文献   

16.
The present study was designed to determine the effects of physiological stress on milk-somatic cell counts (SCC) and function of bovine peripheral blood leukocytes (PBL). Nine healthy lactating cows were used in the examination. Five cows were transported 100 km for 4 hr (transported group; TG), and 4 cows were penned (non-transported group; NTG). Blood and milk samples were collected at 0, 2, and 4 hr after loading, and at 2 hr, and 1, 2, 3, and 6 days after unloading. The following activities were measured: adhesion receptor (CD 18 and L-selectin) expression of neutrophils and monocytes, migration capacity and percentage of apoptotic cells of neutrophils, serum soluble L-selectin (sL-selectin), plasma cortisol, and SCC. A significant increase in plasma cortisol and milk SCC was observed in TG. Leukocytosis, derived from neutrophils was recorded in TG, and was indicated by apoptotic measurement as an increase of young cells from the marginal pool. Increased migration and decreased surface expression of both L-selectin and CD 18 in neutrophils were observed after transportation. Elevated serum sL-selectin was also noted as a result of transportation. The present study indicated that transport stress modulates peripheral blood neutrophil function, particularly enhancing migration capacity, and causes diapedesis across the mammary epithelium. Increased milk SCC in transported cattle might be due to these phenomena, and severe physiological stress may bring about an increase in SCC in milk.  相似文献   

17.
Neutrophils were isolated from the blood and mammary gland of 3 multiparous lactating cows and 3 nulliparous heifers. Neutrophil function was evaluated by phagocytosis and luminol-dependent chemiluminescence. Peroxidase activity was detected by use of transmission electron microscopy. Compared with that for blood neutrophils, percentage of phagocytosis was 9.6% lower for neutrophils isolated from the mammary gland of lactating cows, but this difference was not observed between neutrophils isolated from the mammary gland and from the blood heifers. Similarly, after subtraction of chemiluminescence values in the absence of zymosan, phagocytosing neutrophils from the mammary gland of lactating cows had lower chemiluminescence than did those from the blood of such cows. For heifers, however, chemiluminescent activity by phagocytosing neutrophils obtained from the mammary gland was similar to that of blood neutrophils. Chemiluminescent activity of resting neutrophils from the mammary gland of lactating cows pretreated with cytochalasin B was not inhibited, compared with that of nontreated resting neutrophils (controls). This was attributed to xanthine oxidase activity. Transmission electron microscopy of mammary gland neutrophils from lactating cows revealed peroxidase-positive material associated with milk-fat globule membranes and with phagosomes containing zymosan. Results indicated that ingestion of fat and casein by neutrophils isolated from milk caused a decrease in phagocytic and chemiluminescent activity. Also, luminol-dependent chemiluminescence was not a reliable measure of milk neutrophil function, because of interference by xanthine oxidase.  相似文献   

18.
The leukotoxin of Mannheimia haemolytica has a very high degree of amino acid diversity because the lktA gene has a complex mosaic structure that has been derived by horizontal DNA transfer and intragenic recombination. The objective of the present study was to determine the effect of this amino acid diversity on leukotoxin cytotoxicity against bovine and ovine cell types. This was done by comparing the luminol-dependent chemiluminescence response of bovine and ovine neutrophils after pre-incubation with the various leukotoxin types. The LktA1.1-type leukotoxin associated with bovine serotype A1 and A6 strains differs from the LktA1.2-type leukotoxin produced by ovine serotype A1 and A6 strains at a single amino acid position and has enhanced activity against bovine but reduced activity against ovine neutrophils. These findings, together with the exclusive association of the LktA1.1-type leukotoxin with bovine strains, suggest that this leukotoxin type has an adaptive advantage in the bovine host. Leukotoxins LktA6-LktA10 are associated with ovine strains and have complex mosaic structures and diverse amino acid sequences but similar levels of cytotoxic activity against bovine and ovine neutrophils, respectively. However, ovine neutrophils were more sensitive to the cytotoxic activities of these leukotoxins than were bovine neutrophils. LktA8- and LktA10-type leukotoxins are associated with serotype A2 and A7 strains that are responsible for the majority of ovine disease cases, but LktA6-, LktA7- and LktA9-type leukotoxins are associated with less common serotypes. These findings contribute to the growing body of evidence suggesting that factors other than leukotoxin cytotoxicity are responsible for the full expression of virulence in M. haemolytica. Overall, the extensive recombinational exchanges within the lktA gene of M. haemolytica have had little effect on leukotoxin function which is highly conserved.  相似文献   

19.
Klebsiella strains isolated from the cow and its environment were biochemically and serologically characterized and evaluated for their susceptibility to normal bovine serum. Thirty-one different biotypes of Klebsiella were identified among 288 cattle and environmental strains. Of these, 56.2% were indole-positive, a greater percentage than expected for Klebsiella. Biotypes 1/1/1 and 5/1/1, most frequently isolated and constituting about 37% of the total isolates, would be considered K pneumoniae by standard biochemical typing procedures. Of 65 cattle and environmental strains studied serologically, 11 serotypes, 14 biotypes, and 29 bioserotypes were identified, indicating the diversity of Klebsiella strains present in the herd. When strains from mastitic milk (n = 19) and the environment (n = 22) were compared, no bioserotype distinction or grouping that related to isolation source was obvious. The predominant bioserotype from both sources was 5/1/1-K35 (21.0% and 22.7% of the strains from mastitic milk and the environment, respectively). The growth inhibition by bovine serum of strains isolated from mastitic milk, the environment, and udder skin was similar. However, strains isolated from the mouth and rectum of the cow were significantly (P less than 0.05) more inhibited by serum.  相似文献   

20.
Neutrophils were isolated from the peripheral blood of adult equids (group 1) and were purified on a density gradient of polyvinylpyrrolidone-coated silica gel. A bactericidal assay was developed, using an equine skin isolate of Staphylococcus epidermidis as target bacterium in medium containing pooled fresh equine serum for opsonization. Significant (P less than 0.05) killing was observed after 60 or 120 minutes' incubation. Reduction in bactericidal function of blood neutrophils was not found after incubation with a virulent strain of Mycoplasma felis for 30 or 60 minutes. Similarly, the function of blood and pleural neutrophils of ponies with M felis-induced pleuritis (group 2) was not different from the function of similar neutrophils from sham-inoculated control ponies (group 3). The number of viable M felis organisms was markedly reduced in the presence of fresh equine serum and equine-specific antibodies, but not when the serum was heat inactivated. Equine neutrophils did not phagocytize M felis. Seemingly, M felis did not impair bactericidal activity of equine neutrophils. Therefore, this mechanism does not predispose equids to bacterial pleuritis.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号