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1.
The capacity of hematogenous polymorphonuclear neutrophilic leukocytes (PMNL) to kill Rhodococcus equi was compared in horses of various ages. A radioisotope bactericidal assay was used to determine the capacity of PMNL to kill R equi. Assays were conducted on PMNL from horses in 3 groups: group I, 13 foals with a mean age of 3.3 days; group II, 10 group-I foals at a mean age of 35.7 days; and group III, adult dams of group-I foals. Bacteria were obtained from the lungs of a foal with R equi pneumonia and opsonized with fresh adult equine serum that contained R equi specific antibody. The mean peak percentage of R equi killed by PMNL was 78.9 for group I, 90.1 for group II, and 87.9 for group III. There was no significant difference (P greater than 0.05) among groups; however, 15% of foals in group I (2 foals) had a mean peak percentage of 30.5 killed, which was significantly (P less than 0.05) lower than the percentage for other foals in group I. The results of our investigation indicated that the capacity of PMNL to kill opsonized R equi is similar in neonatal, young, and adult horses. However, some neonatal foals have a substantially lower capacity to kill R equi, which may be an important factor in the pathogenesis of R equi infections.  相似文献   

2.
Polymorphonuclear neutrophil leukocytes (PMNL) from 8 healthy foals (2-14 weeks of age) and 2 foals with bacterial pneumonia were separated from whole blood using a 2 step Percoll gradient. Purified PMNL were tested for bactericidal function against Rhodococcus equi and Staphylococcus aureus in the presence of normal horse serum. The percentage uptake after a 15-min pre-incubation of PMNL and bacteria was also calculated. Ultrastructural examination of the interaction of R. equi and normal foal PMNL was performed after 15 min incubation. Results indicated that foal PMNL effectively phagocytose and destroy R. equi and S. aureus in the presence of normal horse serum. The mean percent uptake for R. equi was 99.3 +/- 0.4% and for S. aureus 99.9 +/- 0.1%. Further, 97.8 +/- 0.1% ingested R. equi and 98.4 +/- 0.1% ingested S. aureus were destroyed in the 15-min incubation period. Over the 3-h incubation, 91.9% of remaining R. equi were killed, but only 49.2 +/- 31.9% of S. aureus (P less than 0.01). Total bactericidal effect of foal PMNL, however, was 99.3 +/- 0.4% against R. equi and 99.9 +/- 0.1% against S. aureus. The percentage uptake and total bactericidal efficacy of neutrophils from sick foals was greater than 95%. Ultrastructural examination of the PMNL-R. equi interaction after 15 min incubation revealed phagocytosis of the bacteria and morphologic changes consistent with neutrophil degranulation. This study suggests that a defect in PMNL bactericidal capability is not likely to be a contributing factor in the pathogenesis of R. equi pneumonia in foals.  相似文献   

3.
The interaction of Rhodococcus equi with alveolar macrophages from adult horses, foals experimentally exposed to R. equi (sensitized foals) and non-exposed foals was studied using in vitro bactericidal assays, cytochemical staining and transmission electron microscopy. It was demonstrated that R. equi is a facultative intracellular parasite, able to survive and multiply within the alveolar macrophages of the host by interfering with phagosome-lysosome fusion. Opsonization of R. equi with antibody against capsular components was associated with increased phagosome-lysosome fusion and significantly enhanced (P less than 0.05) killing of the organism by alveolar macrophages from non-exposed foals. Macrophages from non-exposed foals were able to ingest the non-opsonized organism, but unable to kill greater than 65% of the infective dose by 6 h post-exposure. Alveolar macrophages from sensitized foals behaved as adult macrophages, able to kill greater than 95% of the infective dose by 6 h. Lymphocyte factors, derived by in vitro incubation of sensitized peripheral blood lymphocytes with R. equi surface antigens, enhanced macrophage bactericidal activity. Macrophages from non-exposed foals incubated in the presence of the lymphocyte factors had a 50% increase in killing of R. equi, while sensitized macrophages incubated with lymphocyte factors had a greater than 100% increase in killing capacity.  相似文献   

4.
The aim of this study was to evaluate serum IgG antibody levels and opsonizing activity in foals from pregnant mares immunized with either proteins from an R. equi strain containing virulence-associated protein A (VapA), an immunodominant surface-expressed lipoprotein encoded by a virulence plasmid crucial for virulence in foals, or a whole killed virulent R. equi preparation. Forty-eight pregnant mares were distributed into three groups, i.e. 24 immunized with R. equi VapA protein antigen associated with a water-based nanoparticle adjuvant (Montanide IMS 3012), 8 immunized with whole killed R. equi, and 16 non-immunized as control. Serum IgG and opsonizing capacity were evaluated during pregnancy in mares, and up to day 45 post-delivery in foals in which R. equi infections were recorded in the first 6 months of life. Pregnant mares immunized with virulent R. equi proteins developed higher serum IgG and opsonic activity which were transferred to the foals than either in the whole R. equi immunized or the control group. Four foals developed pneumonia in the control group while none in immunized groups. Results support further evaluation of VapA protein antigen associated with a water-based nanoparticle adjuvant as a candidate vaccine for immunization of pregnant mares resulting in passive antibody-mediated protection of foals.  相似文献   

5.
The immunoprophylactic capacity of specific immune plasma was evaluated in pony foals infected experimentally with Rhodococcus equi. Immune plasma, produced by repeated parenteral administration of viable R. equi to adult horses, was harvested and frozen. Group I (six control foals) and Group II (six principal foals) received lactated Ringers solution and immune plasma respectively at three and five days of age. R. equi were aerosolised into a caudal lung lobe of all foals at seven days of age. Clinical signs, haematological alterations, immune responses, thoracic radiographs and technetium99m pulmonary perfusion scans were monitored. All foals were destroyed and complete post mortem examinations performed. All foals developed pneumonia as evidenced by clinical, radiographic and perfusion alterations, but the survival rate of principal foals was significantly (P less than 0.01) greater than that of control foals. Five control foals developed terminal disease, whereas all principal foals recovered. There was no significant (P greater than 0.05) difference in temperature response, or peripheral blood leucocyte, neutrophil or fibrinogen concentrations between groups. ELISA values for R. equi antibody were significantly (P less than 0.001) greater in principal foals following treatment, but there was no significant (P greater than 0.05) difference in IgG or IgM concentrations between groups. Results of the haemolysis inhibition assay indicated that equi factor neutralising antibodies were transferred by immune plasma to the principal foals. Post mortem examinations of five control foals destroyed at approximately three weeks post infection because of terminal disease, revealed severe pyogranulomatous pneumonia. One control and all principal foals were either free of lesions or had resolving lesions and/or minimal scar formation at three months post infection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

6.
A protein antigen that reacted in the agar gel diffusion (AGD) test and which had equi factor(s) activity, was partially purified from the culture supernatant of Rhodococcus equi by successive column chromatography on diethylaminoethyl cellulose and Sepharose 4B. Employing a standard foal serum, the concentration of this antigen was adjusted for the AGD test. Optimal dilutions of the antigen reacted in the AGD test with sera from foals naturally infected with serologically different R. equi. The antigen prepared was considered suitable for use in field surveys of R. equi infection. Accordingly, four groups of sera were tested: those from 18 foals diagnosed as being infected with R. equi, those from 54 control foals with culture-negative R. equi pneumonia, arthritis or cellulitis, those from 46 diseased foals suspected of having R. equi infection and those from 51 clinically normal foals. A positive precipitation reaction was observed with sera from 100% of the first group, 69.5% of the third group and 17.7% of the fourth group. A negative reaction was obtained with sera from 100% of the second group.  相似文献   

7.
Antibody response of horses to Rhodococcus equi antigens.   总被引：4，自引：1，他引：3       下载免费PDF全文
The antigens extracted from strains belonging to seven capsular serotypes of Rhodococcus equi, as well as from two wild strains isolated from pneumonic foals, were examined. Whole-cell antigens and soluble products present in broth culture supernatants were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electroblotted onto nitrocellulose, and stained with serum from hyperimmunized rabbits or foals. Foal sera used included sera from pneumonic animals with known titer to equi factors; from animals bled monthly on a farm with enzootic pneumonia, and from animals bled monthly on a farm with no history of R. equi pneumonia. The humoral response of foals to somatic antigen preparations was negligible, with few differences noted between sera from healthy, subclinically affected, and sick foals. The humoral response to R. equi broth culture supernatant products appeared more marked and was related to equi factor antibody titer. These findings suggest that the humoral response to R. equi whole-cell antigens is unimportant in protection against disease, which is consistent with the behavior of the organism as a facultative intracellular pathogen.  相似文献   

8.
Humoral immune response to Rhodococcus equi in experimentally infected foals was studied with the enzyme-linked immunosorbent assay (ELISA) method. Class-specific antibodies were measured by ELISA in the sera of foals after intratracheal or oral inoculation with R. equi ATCC 6939 or T 48 and in the lung washings of a foal after intratracheal inoculation or of normal horses. After intratracheal or oral inoculation with R. equi, serum antibodies were first detected in immunoglobulin G (IgG) followed by IgM and IgA classes, but significant levels of IgM and IgA developed only in the foal infected intratracheally with R. equi T 48. Only the foal infected intratracheally with T 48 developed pneumonia. Anti-R. equi IgG and IgA antibodies appeared in lung washings of the intratracheally infected foal. There were differences in the antibody response to R. equi among the intratracheally infected foals, the orally infected foal and the naturally infected foal. These results suggest that the humoral immune response to R. equi may be affected by the type of R. equi strain and the route and extent of R. equi exposure.  相似文献   

9.
Rhodococcus equi produces two exoenzymes (REE), a cholesterol oxidase in large amounts and a phospholipase C, which cause lysis of sheep red blood cells (SRBC) sensitized with Staphylococcus aureus beta toxin. Two immunization studies were done in foals to determine the role of antibody to REE in protection against R. equi pneumonia. In the first study, three foals (mean age 10 days) were vaccinated four times at 2-week intervals with over 1 million units of partially purified exoenzymes (PREE). In the second study, three foals (mean age 19 days) were administered plasma from an adult horse vaccinated with PREE. Relatively low titres (16-32) of neutralizing antibody were detected in the foals of the former group, and passive transfer of neutralizing antibody (titres 32-64) occurred in the latter. Following immunization, principal foals and an equal number of similarly aged nonimmunized foals were challenged by aerosol with 1 x 10(10) live R. equi per day for 5 consecutive days. No severe clinical pneumonia developed in either group and, with one exception, only minor and resolving lung abscesses developed in these foals. These studies showed that antibody response of foals to immunization with PREE was poor, antibody to PREE did not prevent foals from developing lung abscesses following experimental infection, and that foals even as young as 3 weeks of age may be largely refractory to aerosol challenge with virulent R. equi.  相似文献   

10.
The purpose of this study was to determine if colostrum-deprived foals with experimentally induced Rhodococcus equi pneumonia have a decreased severity of the disease and decreased mortality rate when given hyperimmune (HI) R. equi antibody plasma (R. equi titer at least 100 % and virulence-associated protein A [VapA] at least 10000) prophylactically versus when given normal equine plasma (R. equi titer less than 20 % and VapA less than 160). Sixteen colostrum-deprived foals (R. equi titer less than 5 %) each received normal equine plasma in the first 24 hours of life (R. equi titer less than 20 %). At 14 days of age, six foals were given normal equine plasma and 10 foals were given HI plasma. All foals were subsequently infected intrabronchially with a pathogenic strain of R. equi (2.5 x 10 sup 8; organisms) at 21 days of age. Repeated physical examinations, weight measurements, complete blood cell counts, fibrinogen measurements, and thoracic radiographs (ventrodorsal and lateral) were performed to help determine the severity of the disease. Foals given HI plasma had significantly higher R. equi ELISA titers (42.4 %) than those given normal plasma (20.9 %) on the day of experimental infection. Mortality rates and severity of disease were statistically similar (P >.05) for the groups. Although none of the foals was treated with antibiotics, several with severe R. equi pneumonia recovered. Either HI or normal equine plasma administered to foals in the first few weeks of life caused no adverse effects and may be protective against R. equi, although the exact constituent responsible for protection is undetermined and requires further investigation.  相似文献   

11.
This study evaluated the prophylactic effectiveness of hyperimmune plasma (HIP) as an aid in the prevention of pneumonia caused by experimental infection with Rhodococcus equi. Thirty neonatal foals were administered R. equi HIP or saline at 2 days of age and were infected with virulent R. equi at 7 days. All foals developed signs or symptoms of respiratory disease. Radiographic scores on day 28 and neutrophil concentrations on day 49 were significantly greater in control foals, and time to respiratory effort score of 2 or higher was significantly shorter for control foals. Three foals, all in the principal group, died or were euthanized before the end of the study, but there was no significant difference in mortality between groups. VapA titers were significantly greater in principal foals. Administration of R. equi HIP decreased the severity of radiographic lesions and prolonged time to increased respiratory effort due to R. equi-induced pneumonia.  相似文献   

12.
Antibody to equi factor(s) in cases of Corynebacterium equi pneumonia in foals was detected using C. pseudotuberculosis exotoxin sensitized calf red blood cells. The test was standardized using antitoxin produced in rabbits by injection of equi factor(s). All sera from ten foals with culture-diagnosed C. equi pneumonia had antibodies to equi factor(s) (titre range 8-256, mean 74.0) and nine sera from 11 foals with suspected C. equi pneumonia also showed antibodies (titre range 4-512, mean 136.4). Two of five pneumonia foals with transtracheal aspirate cultures not yielding C. equi had such antibodies. Fifty-eight of 59 control horse sera had no antibodies; the one positive serum came from a foal on a farm where C. equi pneumonia was endemic. By contrast only five of 15 foals with experimentally-induced C. equi pneumonia had antibodies to equi factor(s), probably because the acute nature of the disease produced did not mimic the chronic course of the natural disease. Antibody to equi factor(s) can be used in the diagnosis of naturally-occurring corynebacterial pneumonia in foals.  相似文献   

13.
An enzyme-linked immunosorbent assay (ELISA) for detection of serum IgG antibodies against Tween 20-extracted antigen of strain ATCC 6939 was applied in Hidaka, Japan to a total of 752 sick foals showing a variety of signs of infectious disease. An optical density (OD) value of more than 0.3 was tentatively fixed to be positive on the basis of readings made of healthy horse sera in previous studies. During a 2 year study, 138 of the 752 sick foals showed an OD value of 0.3 or higher and were designated as 'suspected of R. equi infection'. Age distribution during the initial medical examination of the 138 seropositive foals was significant in that most (64%) foals were age 31-60 days, with a sharp decrease in subjects beyond that age. Of the 138 foals suspected of having R. equi infection, 34 foals (25%) showed OD values of over 0.9 at the initial medical examination, in addition to high blood leucocyte counts and serum fibrinogen and alpha-globulin values. The infectious foals had been treated with antibiotics just before and after serodiagnosis and 126 foals (91%) recovered from the disease. However, no clinical improvement was observed in 12 foals (9%). At necropsy, these foals revealed suppurative pneumonia and lymphadenitis of gut associated lymph nodes accompanied by abdominal abscesses. All isolates from the pulmonary and abdominal abscesses revealed R. equi. These results suggest that OD readings in the high range are associated with severe disseminated infection with R. equi.  相似文献   

14.
Clarithromycin offers numerous advantages over erythromycin and thus, is an attractive alternative for the treatment of Rhodococcus equi infections in foals. The disposition of clarithromycin was investigated in 6 foals after intragastric administration at a dose of 10 mg/kg body weight. Detectable serum concentrations of clarithromycin were found in 3 of 6 foals at 10 minutes and in all foals by 20 minutes post-administration. Time to peak serum concentration (Tmax) was 1.5 hours and peak serum concentration (Cmax) was 0.92+/-0.17 microg/ml. Mean serum concentrations decreased to 0.03 microg/ml at 24 h. No adverse reactions were noted during or after IG administration in any of the foals. Based on the pharmacokinetic parameters, the MIC90 of R. equi isolates, and predicted steady state concentrations, an oral dose of 7.5 mg/kg given every 12 hours would appear appropriate for the treatment of R. equi infections in foals.  相似文献   

15.
In order to assess the Rhodococcus equi infection in three provinces of Turkey (Bursa, Izmir and Istanbul), 696 sera from healthy foals and adult horses were tested by indirect ELISA using a R. equi reference strain (ATCC 6939) as antigen. 103 sera (14.80%) with titres >0.646 resulted positive. Seroprevalence was significantly higher (P=0.0053) in male than in female horses of Istanbul province, although higher antibody titres (mean value) were observed in the female group of Bursa and Izmir provinces with differences estimated between provinces (P=0.0002). Seroprevalence was correlated with age: foals aged less than 1 year (P<10(-4)) and horses from 5 to 10 years old (P=0.018) resulted more infected in Bursa and Izmir provinces. Our findings indicate that R. equi infection actually occurs in all investigated provinces, suggesting the importance of serological survey to diagnose the infection and to prevent the zoonotic risk.  相似文献   

16.
Bronchoalveolar lavage was performed 5 times, sequentially, on 3 healthy foals while each foal was 6 to 63 days of age. Phagocytosis and bactericidal assays were performed on recovered alveolar macrophages. Corynebacterium equi and alveolar macrophages at a ratio of 10:1 were incubated for 1 hour in medium containing 1% heat-inactivated rabbit anti-C equi serum. After incubation, greater than 90% of the alveolar macrophages contained at least 1 ingested bacterium and each alveolar macrophage contained 9.4 +/- 1.0 bacteria (mean +/- SE). After alveolar macrophages and C equi were incubated for 1 hour in medium containing heat-inactivated pooled normal horse serum, approximately 24% of the alveolar macrophages contained at least 1 bacterium and each alveolar macrophage contained 0.8 +/- 0.7 bacteria. From 6 to 61 days of age, each foal had significantly (P less than 0.05) decreased phagocytic activity by alveolar macrophages, but a significant change in killing of C equi by alveolar macrophages was not found in the foals from 21 to 61 days of age. After incubating alveolar macrophages and C equi for 4 hours in vitro, approximately 75% of ingested C equi remained viable.  相似文献   

17.
The effect on foals of prophylactic administration of hyperimmune plasma to prevent R. equi infection was investigated on three farms at which R. equi infection was endemic. Sixteen foals between 10 and 39 days of age were intravenously given 1-21 of hyperimmune plasma. ELISA antibody titres against R. equi were significantly increased and maintained at high levels for over 30 days in most of the recipient foals. The prevalence of R. equi infection was 6.3% (1/16) in the foals that received the immune plasma, and 26.3% (5/19) in the control foals not given the immune plasma on the three farms. For 2 years before and after this field trial on the three farms, 18 of 64 foals (28.1%) showed clinical signs of respiratory tract infection and four of them died of R. equi pneumonia. Heavy contamination of horses and their environment with virulent R. equi was detected by colony blotting, and plasmid profiles also suggested that foals on the three farms were constantly exposed to virulent R. equi. The results of this field trial support previous observations by some researchers that the administration of hyperimmune plasma to foals in the early days of life promotes prevention of R. equi infection on endemic farms; however, the mechanism of hyperimmune plasma protection remains unclear.  相似文献   

18.
An enzyme-linked immunosorbent assay (ELISA) was used to diagnose Corynebacterium (Rhodococcus) equi infection in foals. In tests done with different antigen-extraction procedures (sodium dodecyl sulfate, sodium deoxycholate, polyoxy-ethylene [9] p-tert-octylphenol, polyoxy-ethylene [9-10] p-tert-octylphenol, sonification, homogenization, and heat treatment at 121 C), Tween 20 was a satisfactory reactive antigen. Using hyperimmune rabbit sera or infected foal sera, we investigated the specificity and the sensitivity of the ELISA with the Tween 20 antigen of the different serotypes or of the isolates. Corynebacterium equi strain ATCC 6939 antigen had the best activity for detecting antibodies to C equi in foals. Sera from 218 healthy horses, 11 healthy foals, 17 healthy newborn foals, a foal with suspected C equi infection, and 5 infected foals were evaluated for antibodies to C equi, using ELISA. The optical density values of 206 healthy horses, 17 healthy newborn foals, and 9 healthy foals were less than 0.1. Infected foal sera, except from foal 3, and serum from a foal with suspected C equi infection had higher optical density values. Using ELISA, specific antibodies against C equi were detected in a naturally infected 6-week-old foal after the foal had a rapid increase in the number of bacteria in the feces and after the initial development of clinical signs of illness at 5 weeks of age. Therefore, ELISA was useful for the early diagnosis of C equi infection in foals.  相似文献   

19.
The aim of this study was to evaluate the usefulness of the previously identified B-cell epitope TSLNLQKDEPNGRASDTAGQ of the VapA protein of Rhodococcus equi and its association with R. equi pneumonia. A modified peptide designated PN11-14 corresponding to the epitope was recognized by all sera from experimentally infected foals with virulent R. equi ATCC103+ containing the virulence plasmid but not by its plasmid-cured derivative ATCC103- strain. Marked levels of VapA-specific immunoglobulin (Ig)G were detected in all sera from the ATCC103+ infected foals at 2 weeks after the infection. One control animal had high titres as determined by the peptide enzyme-linked immunosorbent assay (ELISA), indicating the ELISA may not absolutely differentiate between foals with R. equi pneumonia and healthy exposed foals in farms where the prevalence of disease is high. However, numbers of animals used were small. Further evaluation of the peptide ELISA with field samples is necessary to determine whether the assay is diagnostically useful. This study showed that levels of passive transfer of maternal IgG antibodies to the epitope in newborn foals could be measured. Interestingly, the maternally derived antibodies were found to significantly (P<0.05 by Student's t-test) decline 2 weeks after birth. Seroconversion against naturally occurring VapA expressing R. equi could be detected in some foals at 4 weeks of age. Antibodies to the epitope peaked and were significantly (P<0.05) greater in foals aged between 6 and 8 weeks. These results indicated that the peptide ELISA could be used to monitor anti-VapA antibodies in foals, particularly those at the age of 4-6 weeks. It is possible that the ELISA may be of some use as a diagnostic test on farms where R. equi is non-endemic. Further studies using large number of field samples are needed to verify this assumption.  相似文献   

20.
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