Search Results

You are looking at 1 - 9 of 9 items for

  • Author or Editor: Douglas W. Morck x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract

Objective—To examine the host response toward Porphyromonas levii,by evaluating chemotaxis, phagocytosis, and oxidative burst of bovine macrophages in vitro.

Sample Population—Cultured bovine macrophages obtained from monocytes harvested from blood samples of 15 Holstein steers. Porphyromonas levii was isolated from the foot rot lesion of an acutely affected feedlot steer.

Procedure—Monocytes were cultured for macrophage differentiation over 7 days. Porphyromonas levii was cultured in strict anaerobic conditions for experimentation. Chemotaxis was evaluated by quantifying macrophage migration toward P leviiin Boyden chambers. Phagocytosis was assessed by quantification of macrophages engulfing P levii following incubation with or without anti-P levii serum or purified IgG. Oxidative burst was measured by use of the nitroblue tetrazolium reduction assay.

Results—Chemotaxis toward P levii was not significantly different from control values at any of the tested bacterial concentrations. Phagocytosis of P levii was approximately 10% at a 10:1 bacterium to macrophage ratio and did not change significantly over time. When higher proportions of P levii were tested for phagocytosis, the 1,000:1 bacterium to macrophage ratio had a significant increase, compared with the 10:1 test group. Opsonization of P levii with high-titer anti-P levii serum or anti-P levii IgG produced a significant increase in macrophage phagocytosis. Oxidative production significantly increased compared with control in the 1,000:1 test group only.

Conclusions and Clinical RelevancePorphyromonas levii may evade host detection by decreased chemotaxis, phagocytosis, and oxidative burst by macrophages. Acquired immunity may be beneficial for clearance of P levii foot rot lesions in cattle. (Am J Vet Res 2002;63:757–762)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To investigate the effects of short-chain fatty acids (SCFAs) and pH on neutrophil oxidative burst, phagocytosis, and morphology after exposure to acetate, propionate, butyrate, or succinate at pH 5.5 and 6.7.

Sample Population—Neutrophils isolated from bovine blood samples and Porphyromonas levii, Prevotella spp, and Bacteroides fragilis isolated from lesions of cattle with acute interdigital phlegmon (foot rot).

Procedures—Bacteria were cultured in strictly anaerobic conditions. Bacterial SCFA production was measured with high-performance liquid chromatography. Neutrophils were isolated, stimulated with phorbol 12-myristate 13-acetate (PMA) or opsonized zymosan (OZ), and incubated with dihydroethidium or dichlorofluorescein diacetate to measure production of O2−and H2O2, respectively. Phagocytosis was assessed after exposure to serum-opsonized bacteria. Cellular morphology was assessed with differential staining.

Results—All bacteria produced at least 3 of the 4 SCFAs. Production of both O2− and H2O2 was markedly curtailed in PMA-stimulated neutrophils exposed to SCFA at pH 5.5, compared with production at pH 6.7. Succinate caused a significant dose-dependent decrease in O2− production at pH 6.7 in OZ-stimulated neutrophils. Monoprotic SCFAs elicited a significant increase in H2O2 production in OZ-stimulated neutrophils at pH 6.7 but a significant decrease at pH 5.5. Monoprotic SCFAs significantly increased phagocytosis at pH 6.7 but decreased phagocytic activity at pH 5.5. Cellular necrosis was observed in cells exposed to SCFAs at pH 5.5.

Conclusions and Clinical Relevance—Establishment and persistence of anaerobic bacteria in cattle with foot rot infection may result in part from neutrophil dysfunction secondary to the effects of bacterially secreted SCFA in acidotic microenvironments.

Full access
in American Journal of Veterinary Research

Abstract

Objectives

To determine tilmicosin concentrations in serum and tissues of rabbits given a single dose of 25 mg of tilmicosin/kg of body weight. To examine the effects of tilmicosin treatment (25 mg/kg, SC) in rabbits with pasteurellosis.

Procedure

After receipt of tilmicosin, healthy New Zealand White female rabbits (n = 3 at each time) were euthanatized at 2, 4, 8, 24, 48, and 72 hours for collection of blood samples and tissue specimens; 4 rabbits served as untreated controls. Rabbits (male and female) with pasteurellosis (n = 42) also were treated. Tilmicosin concentration was determined in serum, lung, and uterine tissues. Rabbits with pasteurellosis were treated with tilmicosin. Response was monitored, using bacteriologic culturing and antibiotic resistance and susceptibility testing, and by scoring clinical signs of disease.

Results

Serum tilmicosin concentration reached 1.91 ±0.18 μg/ml after 2 hours, decreased to 0.77 ± 0.07 μg/ml by 8 hours, and was below minimum inhibitory concentrations for Pasteurella multocida at 24 hours. Terminal half-life in serum was 5.97 hours. Lung and uterus concentrations were 14.43 ± 1.34 and 11.57 ± 0.09 ppm at 2 hours, and were 5.10 ± 1.05 and 8.87 ± 1.66 ppm at 24 hours, respectively. 69% (29/42) of rabbits with pasteurellosis responded favorably in 3 days. Second treatment was required in 31% (13/42), and 5 of these rabbits had clinical signs on day 6; 2 of these 5 had improved. Treatment success rate was 93% (39/42). Of the rabbits that were culture positive on day 0, 35% (6/17) remained positive on day 3. 1 of 6 rabbits was culture positive on day 6.

Conclusion

Tilmicosin (25 mg/kg, SC) was an effective treatment for pasteurellosis in New Zealand White rabbits.

Clinical Relevance

Tilmicosin treatment of pasteurellosis in rabbits is useful in research rabbits and in those destined for meat production. A single dose of antibiotic minimizes stress-associated handling. (Am J Vet Res 1996;57:1180-1184)

Free access
in American Journal of Veterinary Research

Objective

To determine duration of infection and association of infection with diarrhea for dairy calves with naturally acquired cryptosporidiosis and giardiosis.

Design

Cohort study.

Animals

20 Holstein calves on a single dairy farm.

Procedure

Fecal samples were collected 3 times/wk for the first 45 days after birth, then weekly until calves were 120 days old and examined for Giardia duodenalis cysts and Cryptosporidium parvum oocysts. Calves were monitored for diarrhea during the first 45 days after birth; during each episode of diarrhea, fecal samples were examined for parasitic, bacterial, and viral pathogens.

Results

All 20 calves shed Giardia cysts and Cryptosporidium oocysts at some time during the study. Mean ages at which Giardia cysts and Cryptosporidium oocysts were first detected were 31.5 and 16.3 days, respectively. Mean number of Giardia cysts in feces remained high throughout the study, whereas Cryptosporidium oocysts decreased to low or undetectable numbers 2 weeks after infection. Eighteen calves had a total of 38 episodes of diarrhea during the first 45 days after birth. Giardia duodenalis was the only pathogen identified during 6 (16%) episodes, C parvum was the only pathogen identified during 9 (24%) episodes, and G duodenalis and C parvum were identified together during 10 (26%) episodes.

Conclusions

Prevalences of giardiosis and cryptosporidiosis were high in these calves, and both parasites were associated with development of diarrhea. Cryptosporidium parvum was an important pathogen when calves were < 1 month old, but G duodenalis was more important when calves were older. Calves cleared C parvum infections within 2 weeks; however, G duodenalis infections became chronic in these calves. (J Am Vet Med Assoc 1999;214:391–396)

Free access
in Journal of the American Veterinary Medical Association

Objective—

To determine whether ceftiofur sodium would be useful for treatment of acute interdigital phlegmon (foot rot) in cattle.

Design—

Randomized controlled trial.

Animals—

308 cross-bred yearling steers with clinical signs of acute interdigital phlegmon (ie, lameness with interdigital swelling, interdigital lesions, or both).

Procedure—

Steers were randomly assigned to 1 of 3 treatment groups: ceftiofur at a dosage of 0.1 mg/kg (0.045 mg/lb) of body weight, IM, every 24 hours; ceftiofur at a dosage of 1.0 mg/kg (0.45 mg/lb), IM, every 24 hours, and oxytetracycline at a dosage of 6.6 mg/kg (3 mg/lb), IM, every 24 hours. All animals were treated for 3 days; treatment was considered successful if animals were no longer lame on day 4. Biopsy specimens were collected prior to treatment from 5 animals in each group and submitted for anaerobic bacterial culture and histologic examination.

Results—

Success rates for the high-dosage ceftiofur (94/129; 73%) and oxytetracycline (87/128; 68%) groups were significantly higher than that for the low-dosage ceftiofur group (5/50; 10%), but there were no significant differences between the high-dosage ceftiofur and oxytetracycline groups. Anaerobic bacteria most frequently isolated from biopsy specimens were Porphyromonas levii and Provetella intermedia.

Clinical Implications—

Use of ceftiofur at a dosage of 1.0 mg/kg for treatment of cattle with acute interdigital phlegmon was as effective as use of oxytetracycline at a dosage of 6.6 mg/kg. However, ceftiofur has a negligible withdrawal time and, therefore, may be a better choice for treatment of near-market weight animals. (J Am Vet Med Assoc 1998;212:254–257)

Free access
in Journal of the American Veterinary Medical Association

Summary:

The prophylactic administration of injectable tilmicosin for pneumonia in weaned beef calves was investigated in 1,806 animals. Comparisons were made among calves receiving an “on-arrival” injection of tilmicosin, calves receiving a single injection of long-acting oxytetracycline, and calves receiving no prophylaxis. Morbidity and mortality attributable to pneumonia, morbidity and mortality attributable to all causes, and case fatality were significantly lower in the group of calves that received tilmicosin, compared with calves that received long-acting oxytetracycline and calves that received no prophylactic antibiotic. Mean time to initial pneumonia treatment was significantly extended in calves that received prophylaxis, compared with those that received no antibiotic on arrival at the feedlot. Calves that received tilmicosin gained significantly more weight than calves that received oxy tetracycline. Calves that were not treated for pneumonia during the trial period gained significantly more weight than did those calves that were treated for pneumonia regardless of experimental group.

The majority of mortalities were attributable to fibrinous pneumonia (31/34). Important bacterial isolates (Pasteurella spp, Haemophilus somnus, Actinomyces pyogenes) obtained at necropsy did not have resistance to tilmicosin in association with administration of tilmicosin as prophylaxis for pneumonia. However, bacterial resistance to trimethoprim/sulfonamide and to oxytetracycline were commonly found in these postmortem isolates.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the effects of oral administration of tilmicosin in piglets experimentally infected with Actinobacillus pleuropneumoniae.

Animals—Forty 3-week-old specific-pathogen free piglets.

Procedure—Piglets were assigned to 1 of 4 groups as follows: 1) uninfected sham-treated control piglets; 2) infected untreated piglets that were intratracheally inoculated with 107 CFUs of A pleuropneumoniae; 3) infected treated piglets that were intratracheally inoculated with A pleuropneumoniae and received tilmicosin in feed (400 ppm [µg/g]) for 7 days prior to inoculation; or 4) infected treated piglets that were intratracheally inoculated with A pleuropneumoniae and received chlortetracycline (CTC) in feed (1,100 ppm [µg/g]) for 7 days prior to inoculation. Bronchoalveolar lavage (BAL) fluid and lung tissue specimens of piglets for each group were evaluated at 3 or 24 hours after inoculation. For each time point, 4 to 6 piglets/group were studied.

Results—Feeding of CTC and tilmicosin decreased bacterial load in lungs of infected piglets. Tilmicosin delivered in feed, but not CTC, enhanced apoptosis in porcine BAL fluid leukocytes. This was associated with a decrease in LTB4 concentrations in BAL fluid of tilmicosin-treated piglets, compared with untreated and CTC-treated piglets, and also with a significant decrease in the number of pulmonary lesions. Tilmicosin inhibited infection-induced increases in rectal temperatures, as measured in untreated and CTC-treated piglets. Pulmonary neutrophil infiltration and prostaglandin E2 concentrations in the BAL fluid were not significantly different among groups at any time.

Conclusions and Clinical Relevance—Oral administration of tilmicosin to infected piglets induces apoptosis in BAL fluid leukocytes and decreases BAL fluid LTB4 concentrations and inflammatory lung lesions. (Am J Vet Res 2005;66:100–107)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate immunomodulatory properties of all-trans retinoic acid and a fully oxidized β-carotene dietary product in calves with Mannheimia haemolytica–induced pneumonia.

Animals—Twenty-five 6- to 10-week-old male Holstein calves for experimental inoculations and three 8- to 30-week-old Angus heifers for blood donations.

Procedures—In vitro, neutrophils and monocyte-derived macrophages isolated from blood of healthy Angus heifers were treated with all-trans retinoic acid (1μM) or fully oxidized β-carotene (8.3 μg/mL) for various times and assessed for markers of cellular death, antimicrobial function, and production of proinflammatory leukotriene B4. Following 28 days of dietary supplementation with fully oxidized β-carotene, Holstein calves were experimentally inoculated with M haemolytica. Bronchoalveolar lavage fluid was collected at 3 and 24 hours after challenge inoculation and analyzed for markers of apoptosis.

Results—In vitro, all-trans retinoic acid and fully oxidized β-carotene induced cell-selective, caspase-3–dependent apoptosis in neutrophils, which subsequently enhanced efferocytosis in macrophages. Conversely, neither treatment altered phorbol 12-myristate 13-acetate–induced oxidative burst, phagocytosis of nonopsonized zymosan (complement or antibody independent), or M haemolytica–induced leukotriene B4 production in bovine neutrophils. In vivo, fully oxidized β-carotene enhanced leukocyte apoptosis in bronchoalveolar lavage fluid as well as subsequent efferocytosis by macrophages without altering numbers of circulating leukocytes.

Conclusions and Clinical Relevance—Neutrophil apoptosis and subsequent efferocytosis by macrophages are key mechanisms in the resolution of inflammation. Findings for the present study indicated that all-trans retinoic acid and fully oxidized β-carotene could be novel nutraceutical strategies that may confer anti-inflammatory benefits for cattle with respiratory tract disease.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To investigate the anti-inflammatory and immunomodulatory properties of tulathromycin in vitro and in experimental models of Actinobacillus pleuropneumoniae–induced pleuropneumonia and zymosan-induced pulmonary inflammation in pigs.

ANIMALS Blood samples from six 8- to 30-week-old healthy male pigs for the in vitro experiment and sixty-five 3-week-old specific pathogen–free pigs.

PROCEDURES Neutrophils and monocyte-derived macrophages were isolated from blood samples. Isolated cells were exposed to tulathromycin (0.02 to 2.0 mg/mL) for various durations and assessed for markers of apoptosis and efferocytosis. For in vivo experiments, pigs were inoculated intratracheally with A pleuropneumoniae, zymosan, or PBS solution (control group) with or without tulathromycin pretreatment (2.5 mg/kg, IM). Bronchoalveolar lavage fluid was collected 3 and 24 hours after inoculation and analyzed for proinflammatory mediators, leukocyte apoptosis, and efferocytosis.

RESULTS In vitro, tulathromycin induced time- and concentration-dependent apoptosis in neutrophils, which enhanced their subsequent clearance by macrophages. In the lungs of both A pleuropneumoniae– and zymosan-challenged pigs, tulathromycin promoted leukocyte apoptosis and efferocytosis and inhibited proinflammatory leukotriene B4 production, with a concurrent reduction in leukocyte necrosis relative to that of control pigs. Tulathromycin also attenuated the degree of lung damage and lesion progression in A pleuropneumoniae–inoculated pigs.

CONCLUSIONS AND CLINICAL RELEVANCE Tulathromycin had immunomodulatory effects in leukocytes in vitro and anti-inflammatory effects in pigs in experimental models of A pleuropneumoniae infection and nonmicrobial-induced pulmonary inflammation. These data suggested that in addition to its antimicrobial properties, tulathromycin may dampen severe proinflammatory responses and drive resolution of inflammation in pigs with microbial pulmonary infections.

Full access
in American Journal of Veterinary Research