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1.
The serum antileukotoxin antibody response and protection against subsequent experimental challenge with Fusobacterium necrophorum were investigated in 30 steers vaccinated with crude F. necrophorum leukotoxoid. Culture supernatant of F. necrophorum, strain 25, containing leukotoxoid was concentrated. The steers were assigned randomly to six groups (n=5): PBS control with Stimulon adjuvant; vaccinated with concentrated supernatant diluted to provide 2.5, 5.0, 10.0, or 20.0 ml with the watersoluble Stimulon adjuvant; and 5.0 ml with the Ribi oil-emulsion adjuvant. The steers were injected subcutaneously on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titres. On day 42, all the steers were challenged intraportally with F. necrophorum culture. Three weeks later (day 63), the steers were killed and necropsied for examination of their livers and assessment of protection. Steers vaccinated with crude leukotoxoid tended to have higher antileukotoxin titres than the controls, but the difference was not significant. Also, the antibody titre did not appear to be dose-dependent. In the control group, 3 out of 5 steers developed liver abscesses. The incidence of liver abscesses in steers vaccinated with Stimulon adjuvant was not dose related; however, only 8 of the 25 vaccinated steers developed abscesses. None of the steers vaccinated with the 5.0 ml dose with Ribi had any abscesses. Evidence for a relationship between antileukotoxin antibody and protection was shown by the lower titre in those steers that developed abscesses compared to those that did not. It was concluded that antileukotoxin antibody titres probably provided some degree of protection against experimentally induced liver abscesses, but further dose-titration studies using Ribi or possibly another more effective adjuvant will be needed to confirm this.Abbreviations BHI brain-heart infusion - CFU colony-forming units - ELISA enzyme-linked immunosorbent assay - MTT 3-[4,5-(dimethylthiazol-2-yl)]-2,5-diphenyltetrazodium] bromide - PBS phosphate-buffered saline - PMN polymorphonuclear neutrophils  相似文献   

2.
Fusobacterium necrophorum, a gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two types of F. necrophorum, subspecies necrophorum (biotype A) and funduliforme (biotype B), have been recognized, which differ morphologically, biochemically and biologically. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis) such as bovine hepatic abscesses and ruminant foot abscesses. Subspecies necrophorum strains are considered to be more virulent for cattle and have been shown to produce greater amounts of leukotoxin than subspecies funduliforme strains. The leukotoxin operon of F. necrophorum consists of three genes (lktBAC) of which the leukotoxin structural gene (lktA) is the second gene in the operon. In this study, the promoter regions of the leukotoxin operons from the two subspecies were identified and their nucleotide sequence compared. The promoter regions were found to differ in sequence, in length of the sequence between the upstream determinant (oppF) and the first gene of the leukotoxin operon (lktB), and in promoter strength as assayed in Escherichia coli host cells.  相似文献   

3.
To analyze immunodominant regions of leukotoxin protein of Fusobacterium necrophorum strain H05, a series of truncated forms of leukotoxin gene were expressed in Escherichia coli using the vector pGEX-6p-1 or pPROEX HTa. The results of SDS-PAGE showed the truncated forms PL1, PL2, PL4, and PL5 were expressed in Escherichia coli using the vector pGEX-6p-1, and the truncated forms PL3 was expressed in Escherichia coli using the vector pPROEX HTa. These recombinant proteins were able to react with antisera against Fusobacterium necrophorum strain A25. In five recombinant proteins, the recombinant proteins PL1, PL3 and PL4 as vaccine were able to elicit formation of the better protective effects on mice against infection of Fusobacterium necrophorum strain A25.  相似文献   

4.
Lameness in the dairy industry in New Zealand causes a problem in lost production, animal welfare and associated costs. To understand what bacteria may be present on the hooves of lame dairy cattle in this grass-fed system, samples were scraped from lame dairy cows and examined for the presence of Fusobacterium necrophorum (F. necrophorum) and Dichelobacter nodosus (D. nodosus) using the polymerase chain reaction (PCR). The PCR primers were designed to detect the presence of the lktA gene, which encodes a leukotoxin unique to F. necrophorum, and the fimA gene of D. nodosus. A total of 148 hoof scrapings were collected by farm staff over the period September 2005 to May 2006. F. necrophorum was detected in 79/148 of the samples, while D. nodosus was detected in 7/148 of the samples. The frequent finding of F. necrophorum within dairy herds in New Zealand is noteworthy and the occasional finding of D. nodosus on some dairy cattle suggests a possible role in both ovine and bovine hoof pathology.  相似文献   

5.
Bacteriologic and histologic studies of hepatic abscesses in cattle   总被引：6，自引：0，他引：6  
Twenty-eight abscessed livers were collected from feedlot cattle at an abattoir; specimens were obtained from 49 abscesses for bacteriologic culture and for histologic examination. Cultural procedures included techniques to enumerate and isolate facultative and obligate anaerobic bacteria. Anaerobic bacteria were isolated from all 49 abscesses, whereas facultative bacteria were isolated from only 22. Mean bacterial counts for anaerobic and facultative bacteria were 3 X 10(8) and 8 X 10(8) bacteria/g of purulent material, respectively. Fusobacterium necrophorum, the only anaerobe isolated, was detected in 100% of the abscesses. Fusobacterium necrophorum biotype A was isolated from 57% of the abscesses (in pure culture from 75%), and F necrophorum biotype B was isolated from 47% of the abscesses (from 96% with mixed infections). Corynebacterium pyogenes was the predominant facultative bacterium isolated. Histologic changes in abscesses were qualitatively similar; abscesses were pyogranulomatous, with a necrotic center surrounded by zones of inflammatory tissue. However, the severity of lesions varied, depending on the F necrophorum biotype involved. Portal triad fibrosis and bile-duct proliferation were most severe in biotype A and mixed biotype B infections and less severe in abscesses from which biotype B was isolated in pure culture.  相似文献   

6.
Retention of the fetal membranes and post‐partal endometritis (RFM) are common problems in dairy cows. Treatment often includes manual removal of the placenta in combination with antibiotic treatment. Earlier studies have shown that cows with endometritis post‐partum have a strong tendency to recover spontaneously. The present study focused on treatments of post‐partal endometritis with the prostaglandin synthesis inhibitor, flunixin (F) either alone or combined with oxytetracycline (T). The study was conducted in two experiments, using 12 primiparous cows in each. As a model for RFM, premature parturition was induced in late pregnant heifers by injecting PGF2α (25 mg i.m.) twice with a 24 h interval. In each experiment the cows were set into four groups and treated with either T (10 mg/kg BW i.m. once daily), F (2.2 mg/kg BW p.o. twice daily), a combination of T and F (dosage, as above) or conservatively (group 0, no drugs). The treatment periods lasted from days 11–14 post‐partum in experiment 1 (groups T1, F1, TF1 and 0) and from days 3–6 post‐partum in experiment 2 (groups T2, F2, TF2 and 0). Jugular vein blood samples were collected for analyses of flunixin and total white blood cells. Uterine biopsies were collected twice weekly for investigation of endometrial microbiology. Rectal palpation and ultrasonographic examinations were performed three times weekly for investigations of uterine involution and ovarian activity. No attempts were made to remove the placentas manually. The experiment lasted until day 56 post‐partum. The induction of parturition was successful in all heifers and 22 of 24 animals had RFM. All RFM cows had bacterial endometritis. The predominant bacteria were Escherichia coliα‐haemolytic streptococci, Fusobacterium necrophorum, Arcanobacterium (Actinomyces) pyogenes, Bacteroides spp., Pasteurella spp. and Proteus spp. Fusobacterium necrophorum and A. pyogenes could be isolated for 3–5 weeks post‐partum and E. coli, Pasteurella and Proteus could be isolated for 2–3 weeks post‐partum. Animals treated with tetracycline after placental shedding (T1 and TF1) had a more rapid recovery from infections with A. pyogenes and F. necrophorum than animals that were not treated with tetracycline. No other genera were affected. Antibiotic treatment before placental shedding (T2 and TF2) did not shorten the uterine infection but altered the bacterial flora, seen as an overgrowth of Proteus spp. (p < 0.05) and increased frequency of Pasteurella (p < 0.05). The α‐haemolytic streptococci were less common in T2 and TF2 than in other groups (NS). Antibiotic treatment of cows before placental shedding (T2 or TF2, n=6) postponed detachment of placenta compared to cows were no antibiotics were administered before placental shedding (T1, TF1, F1, F2 and 0, n=16, 9.8 days pp (median) versus 11.8, p=0.004). Neither treatment shortened uterine involution. Flunixin treatments did not seem to influence recovery from infection or uterine involution. It was concluded that early oxytetracycline treatment of retained fetal membranes in the cow did not shorten the uterine involution or uterine infection but it did slow down the detachment process of the retained placenta. Oxytetracycline treatment after placental shedding might shorten the uterine infection but otherwise did not affect the clinical results. Flunixin treatment had no influence on the clinical outcome of the disease.  相似文献   

7.
The aim of this study was to determine which of the two species, Fusobacterium necrophorum or Dichelobacter nodosus, are associated with hoof thrush in horses. Fourteen hoof samples, collected from eight horses with thrush and 14 samples collected from eight horses with healthy hooves, were examined for the presence of F. necrophorum, Fusobacterium equinum and D. nodosus. Only isolates with phenotypic characteristics representing Fusobacterium could be cultured. Total DNA extracted from the 28 hoof samples was amplified by using DNA primers designed from gene lktA, present in F. necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme and F. equinum, and gene fimA, present in D. nodosus. The lktA gene was amplified from five of the 14 infected hoof samples and from one hoof sample without thrush. The DNA sequence of the amplified ltkA gene was identical to the lktA gene of the type strain of F. necrophorum (GenBank accession number AF312861). The isolates were phenotypically differentiated from F. equinum. No DNA was amplified using the fimA primer set, suggesting that F. necrophorum, and not D. nodosus, is associated with equine hoof thrush. Hoof thrush in horses is thus caused by F. necrophorum in the absence D. nodosus. This is different from footrot in sheep, goats, cattle and pigs, which is caused by the synergistic action of F. necrophorum and D. nodosus.  相似文献   

8.
An attempt was made to develop a vaccine against salmonellosis in poultry by formalizing the Salmonella toxins (enterotoxin plus cytotoxins) that have been found to be the main virulent products of the organisms. Formalized (FT) and carbonated (CT) toxoids were prepared from partially purified toxins of Salmonella enterica subspecies enterica ser. Weltevreden (BM-1643) and S. enterica ser. Gallinarum (L-19/a). There was no mortality in birds vaccinated with formalized toxoid of serovar Weltevreden plus Freund's complete adjuvant (FCA) following homologous or heterologous (S. enterica ser. Gallinarum and S. enterica ser. Typhimurium) challenges. Protection ranged from 50% to 83.3% in the groups immunized with other preparations of S. enterica ser. Weltevreden, i.e. with FT without FCA or with CT with or without FCA. Formalized toxoid prepared from S. enterica ser. Gallinarum (FTSG) toxins given with FCA afforded 100% protection against homologous challenge, but not against heterologous serovars. In the control group, only 16.7% of the birds survived in a subgroup challenged with S. enterica ser. Gallinarum, and none withstood challenge with S. enterica ser. Weltevreden or S. enterica ser. Typhimurium. No untoward reactions were observed in any of the immunized groups. Thus, the vaccine was considered to be potent and safe.  相似文献   

9.
坏死梭杆菌是动物和人的各种坏死化脓感染的条件性致病菌.坏死梭杆菌的白细胞毒素是一种高度不稳定性分泌蛋白,被认为是主要的毒力因子.坏死梭杆菌白细胞毒素基因的开放阅读框(lktAORF)包括9 726 bp,编码3 241个氨基酸,总分子质量为336 ku的蛋白,且与其他细菌的细胞毒素没有任何相似的序列.覆盖在整个坏死梭杆菌lktA ORF上的5个短的重叠的多肽分别是BSBSE,SX,GAS,SH和FINAL,将它们在大肠埃希菌中表达,所有的多肽都有免疫原性,但GAS引起最小的抗体反应,BSBSE和SH对坏死梭杆菌攻击诱导产生了很强的保护力,比坏死梭杆菌的培养上清内全长活性lkt或无活性上清的保护性要好得多.  相似文献   

10.
The effect of cultural conditions on the production of leukotoxin by biotypes A and B of F. necrophorum was investigated. Biotypes A and B were grown in prereduced, anaerobically sterilized, brain-heart infusion (BHI) broth. The average leukotoxin titer of culture supernatant was 18 times higher from biotype A strains than from biotype B strains. Leukotoxin activity peaked during the late-log and early-stationary phases of growth, then declined precipitously in both biotypes. F. necrophorum biotype A was grown in different media (BHI, liver infusion, and Eugon broths), at various pH (6.6, 7.3, 7.7, and 8.2), incubation temperatures (30, 35, 39, and 43 degrees C), redox potentials (-352 to +375 mV), and iron concentrations (less than 0.2, 4.2, 42.1, and 361.4 microM). Anaerobic BHI broth with pH from 6.6 to 7.7 at 39 degrees C incubation temperature supported maximal F. necrophorum growth and leukotoxin production. The optimum redox potential for F. necrophorum growth was in the range of -230 to -280 mV. However, the presence of titanium III citrate or dithiothreitol (7.78 mM) in the medium decreased (P less than 0.05) the leukotoxicity of F. necrophorum. Low iron concentration (less than 0.2 microM) decreased (P less than 0.05) growth rate but not leukotoxin activity of F. necrophorum, whereas high iron concentration inhibited the leukotoxin activity.  相似文献   

11.
The spread of benzimidazole-resistant nematodes in dairy goat farms is of a great concern as probably more than 70% of the flocks are involved. As there are very few other anthelmintic options during the lactating period, we have evaluated the efficacy of copper oxide needles (CON, Copinox, Bayer, UK) in both experimental and natural infections in goats. The curative effect of CON (2–4 g) on existing worm burdens was assessed in goats experimentally infected with Teladorsagia circumcincta, Haemonchus contortus and Trichostrongylus colubriformis, compared to controls. The preventive effect of CON (4 g) on worm establishment was monitored for 2 months in animals experimentally infected with H. contortus and for 3 months in naturally infected animals on a farm exhibiting predominant infections with T. circumcincta and Oesophagostomum venulosum. In both experimental and natural conditions, the efficacy of CON was nil against Teladorsagia, Trichostrongylus and Oesophagostomum infections. In contrast, the efficacy of CON against Haemonchus was clearly established in reducing the worm burden (75%) as well as in lowering the egg output (37–95%) in relation to the establishment of new infections over several weeks. Copper oxide needles may represent an alternative to conventional anthelmintics in the control of Haemonchus infection in some goat farms.  相似文献   

12.
Epidemiological data indicate that infection of cattle with chlamydiae such as Chlamydophila (C.) pecorum, C. abortus, C. psittaci and Chlamydia suis, is ubiquitous with mixed infections occurring frequently. The apparent lack of association between infection and clinical disease has resulted in debate as to the pathogenic significance of these organisms, and their tendency to sub-clinical and/or persistent infection presents a challenge to the study of their potential effects. However, recent evidence indicates that chlamydial infections have a substantial and quantifiable impact on livestock productivity with chronic, recurrent infections associated with pulmonary disease in calves and with infertility and sub-clinical mastitis in dairy cows. Data also suggest these infections manifest clinically when they coincide with a number of epidemiological risk factors. Future research should: (1) use relevant animal models to clarify the pathogenesis of bovine chlamydioses; (2) quantify the impact of chlamydial infection at a herd level and identify strategies for its control, including sub-unit vaccine development; and (3) evaluate the zoonotic risk of bovine chlamydial infections which will require the development of species-specific serodiagnostics.  相似文献   

13.
Post‐partum period has an important role in cows' breeding due to its effects on reproductive efficiency and subsequent pregnancy. Escherichia coli, Trueperella pyogenes (Arcanobacterium pyogenes), Fusobacterium necrophorum and Prevotella melaninogenicus are recognized as major pathogens associated with uterine endometrial lesions. The objective of this study was to identify these pathogens using the polymerase chain reaction (PCR) as a culture‐independent sensitive method. A total of 172 cows were examined 25–35 days post‐partum, and 128 cows were examined at 2 weeks later (39–49 days post‐partum). Uterine discharges were collected by covered plastic infusion pipettes. The prevalence of endometritis was greater in the first examination than the second (35.5% vs. 16%). E. coli was detected in eight of the samples, T. pyogenes was detected in 13 of the samples and F. necrophorum was detected in 11 of the samples. There was no positive sample of P. melaninogenicus. Uterine contamination by T. pyogenes and F. necrophorum in the first examination was higher than the second examination. T. pyogenes affected as a tendency the prevalence of clinical endometritis in first examination. Primiparous cows showed 4.02 times higher odds of clinical endometritis compared with second‐parity cows in first examination. A multiplex PCR protocol as a simple, less expensive, fast assay was introduced to identify E. coli, T. pyogenes and F. necrophorum.  相似文献   

14.
Fusobacterium necrophorum, a gram-negative, anaerobic and rod-shaped bacterium, is generally an opportunistic pathogen and causes a wide variety of necrotic infections in animals and humans. Leukotoxin, a secreted protein, is a major virulence factor. The gene encoding the leukotoxin (lktA) in F. necrophorum has been cloned, sequenced and expressed in Escherichia coli. Because of low expression levels, problems associated with purifying full-length recombinant protein, and of the physical instability of the protein, five overlapping leukotoxin gene truncations were constructed. The recombinant polypeptides (BSBSE, SX, GAS, SH, and FINAL) were expressed in E. coli and purified by nickel-affinity chromatography. The objectives were to investigate the effectiveness of the purified truncated polypeptides to induce protective immunity in mice challenged with F. necrophorum. The polypeptides, individually or in combination, and inactivated native leukotoxin or culture supernatant of F. necrophorum were homogenized with an adjuvant and injected into mice on days 0 and 21. Blood samples were collected to measure serum anti-leukotoxin antibody titers on days 0, 21 and 42 and on day 42, mice were experimentally challenged with F. necrophorum. All polypeptides were immunogenic, with GAS polypeptide eliciting the least antibody response. Two polypeptides (BSBSE and SH) induced significant protection in mice against F. necrophorum infection. Protection was better than the full-length native leukotoxin or inactivated supernatant.The study demonstrated that the leukotoxin of F. necrophorum carries epitopes that induce protective immunity against experimental fusobacterial infection, thus providing further evidence to the importance of leukotoxin as a major virulence factor.  相似文献   

15.
Six, 5- to 10-week-old male Holstein calves were inoculated intratracheally with 5 x 10(9) logarithmic growth phase Pasteurella haemolytica biotype A serotype 1 (A1). Immunohistochemical techniques in conjunction with the use of monoclonal antibodies directed against P. haemolytica A1-derived lipopolysaccharide (LPS), capsular polysaccharide, and a polyclonal rabbit anti-leukotoxin antibody were used to localize their respective antigens in tissue sections of pneumonic lung at the light and electron microscopic levels. We found the following: 1) LPS, capsular polysaccharide, and leukotoxin were released into the inflammatory exudate; 2) LPS was found within the cytoplasm of neutrophils (located in the alveolus and alveolar wall), alveolar macrophages, endothelial cells, pulmonary intravascular macrophages, and on epithelial cell surfaces; 3) capsular polysaccharide was found in the alveolus and alveolar macrophages but not in cells of the alveolar wall; and 4) leukotoxin was associated with cell membranes of degenerating inflammatory cells located in the alveolus. This is the first study that demonstrates the presence of leukotoxin in the pulmonary inflammatory lesions caused by P. haemolytica A1 and implicates endotoxin as an important factor in the genesis of the pulmonary lesions.  相似文献   

16.
A monoclonal antibody-based sandwich immunoassay (mAb sandwich ELISA) was developed for the detection of Fasciola hepatica antigen in the faeces of cattle. The assay was applied to samples from 100 cattle infected with F hepatica, 56 animals with parasitologically proven infections of other parasites and 100 uninfected animals. F hepatica antigen was detected in all the faecal samples from animals with fasciolosis, but none of the samples from the uninfected animals or from those with other parasitic infections had significant levels of F hepatica antigens. The results indicate that the mAb sandwich ELISA is a rapid, simple and useful method for the diagnosis of active F hepatica infection in cattle.  相似文献   

17.
The genetic structure of β-haemolytic Lancefield group C streptococci isolated from horses in Australia was examined by multilocus enzyme electrophoresis. The 249 isolates comprised 70 classified phenotypically as Streptococcus equi subspecies equi, 177 classified as S equi subspecies zooepidemicus and two which were unclassifiable. Forty-one electrophoretic types were identified which could be classified into three major clusters, A, B and C. Of the isolates, 178 fell into cluster B (types 4 to 22) and lay within a genetic distance of 0·36. Sixty-nine of the 70 S equi subspecies equi isolates fell into type 12, which suggests that they were members of a single clone, and the isolates from abscesses were significantly more likely to belong to type 12 than those from horses with no clinical signs (P<0·001). There were no other significant associations between electrophoretic types or clusters and the isolation of the organism from particular sites. These data suggested that S zooepidemicus may be the archetypal species from which the clone designated subspecies equi has been derived. If isolates of the subspecies equi from other geographical regions also prove to be members of electrophoretic type 12, this hypothesis would be strengthened.  相似文献   

18.
Fusobacterium equinum, a gram negative, rod-shaped and an obligate anaerobic bacterium is a newly described species. The organism is associated with necrotic infections of the respiratory tract in horses that include necrotizing pneumonia, pleuritis and paraoral infections. The species is closely related to F. necrophorum that causes liver abscesses in cattle and sheep, calf-diphtheria in cattle, and foot-rot in sheep and cattle. Leukotoxin, an exotoxin, is an important virulence factor in bovine strains of F. necrophorum. Our objective was to examine strains (n=10) of F. equinum for leukotoxin (lktA) gene and its toxic effects on equine leukocytes. Southern hybridization and partial DNA sequencing revealed that all the 10 strains had the lktA gene with greater similarities to F. necrophorum subsp. necrophorum. The secreted leukotoxin was detected in the culture supernatant and its biological activity was determined by viability assays with equine polymorphonuclear cells (PMNs) using flow cytometry. While culture supernatants of four strains (E1, E7, E9, and E10) were highly toxic to equine PMNs; strain E5 was moderately toxic and the remaining strains (E2, E3, E4, E6, and E8) were only mildly toxic. Our data indicated that F. equinum isolates had lktA gene and its product was toxic to equine leukocytes. Therefore, leukotoxin may be an important virulence factor in F. equinum infections.  相似文献   

19.
SUMMARY The decrease in the prevalence of Corynebacterium pseudotuberculosis after two generations of vaccination against the disease it causes, was used to estimate the rate of control of caseous lymphadenitis (CLA). Three groups of 150 sheep, of which 50 in each group were artificially infected with C pseudotuberculosis and 100 in each group were uninfected sheep, were run separately for 40 months and shorn 5 times to promote the spread of CLA. One lot of 50 infected sheep and 2 lots of 100 uninfected sheep were vaccinated against CLA. The rate of spread of CLA was recorded. Sheep vaccinated against CLA and naturally exposed to infection had a 74% lower infection rate than unvaccinated sheep. Sheep vaccinated against CLA and exposed to only vaccinated infected sheep had a 97% lower infection rate. Unvaccinated sheep had a 76% infection rate, with 77% of the transmission occurring at the 4th and 5th shearings, without any discharging CLA abscesses being observed. This study supports the view that in Australian wool producing flocks, CLA spreads mainly from sheep with discharging lung abscesses to sheep with shearing cuts. Vaccinated sheep infected with CLA have 96% fewer lung abscesses compared with unvaccinated infected sheep and are therefore less likely to spread this disease to other sheep .  相似文献   

20.
Pneumonic pasteurellosis is a common respiratory infection in cattle that has major economic and welfare implications world-wide and the incidence in the UK due to Pasteurella multocida, currently the same as that associated with Mannheimia haemolytica, is increasing. Whereas much is known regarding the pathogenesis of M. haemolytica infections little information is available on the pathogenic process of pasteurellosis initiated by P. multocida. In the present work calf systemic and innate immune responses to intratracheal challenge with formalin-killed P. multocida biotype A:3 and to subsequent experimental lung infection with live P. multocida were investigated. Eight-week-old calves were challenged intratracheally on day 0 with either 109 colony forming units (cfu) of formalin-killed P. multocida biotype A:3 in 300 ml saline (n=10) or 300 ml saline alone (n=10), followed, at day 21, by challenge with 109 cfu live P. multocida. Pathophysiological and lung phagocyte responses were assessed by clinical monitoring, sequential lung lavage and blood sampling. Results for samples obtained before, during and after challenge showed clinical and acute phase protein responses to both bacterial culture and saline control treatments, although higher responses were associated with bacterial challenge. Phagocytosis of P. multocida during 1 h incubation periods with lavaged cells in vitro was unaffected by exposure in vivo to killed P. multocida and there was evidence that P. multocida was able to survive intracellularly during this assay. There was no indication that lung exposure to formalin-killed P. multocida conferred protection against subsequent homologous live challenge.  相似文献   

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