Evaluation of PCR based on gene apxIVA associated with 16S rDNA sequencing for the identification of Actinobacillus pleuropneumoniae and related species

The pleuropneumonia caused by Actinobacillus pleuropneumoniae (App) is one the most important swine respiratory diseases. Biochemical and serological tests are widely applied for App diagnosis and characterization. However, in some isolates, conflicting results are found. The present work focus on the characterization of 29 isolates biochemically classified as A. pleuropneumoniae, collected from swine in herds with or without a clinical history of pleuropneumonia. Sixteen isolates were from healthy swine, initially classified as nonserotypable A. pleuropneumoniae; they displayed differences in the molecular characterization patterns of App (genes cpx and apxI, II, and III). Those bacteria that could not be serotyped were submitted to rDNA 16S sequencing. All 29 isolates were analyzed by PCR for the presence of the apxIVA gene. Thirteen isolates (45%) were confirmed to be A. pleuropneumoniae by PCR, nine being from diseased animals (31%) and four from healthy animals (14%) with conclusive serotyping. The rDNA 16S sequencing was used to classify the other 16 isolates in related species other than A. pleuropneumoniae, resulting in eleven A. minor, three A. porcinus, and two Pasteurella sp. Because of conflicting results between biochemical tests and rDNA 16S sequencing, the biochemical characterization was repeated, and the new results were in agreement with the rDNA 16S sequencing data. Biochemical characterization proved to be efficient for the majority of the A. pleuropneumoniae isolates. Nevertheless, conventional tests can render conflicting results, and other methodologies, such as amplification of A. pleuropneumoniae specific apxIVA gene and rDNA 16S sequencing, are very useful for improved classification. We also observed a great variety in rDNA 16S sequences from different A. minor isolates.

Histochemical and lectinhistochemical studies on nasal mucosa of pigs with or without respiratory diseases

Histochemical and lectinhistochemical examinations were carried out on nasal mucosa of pigs with or without respiratory diseases. As the results, both acid and neutral mucins coexisted in nasal mucosa of normal pigs while acid sialomucins were mainly observed in nasal mucosa of pigs infected with Bordetella bronchiseptica and/or Pasteurella multocida. Lectinhistochemistry revealed that the nasal epithelial cells of normal pigs were rich in N-acetylgalactosamine, fucose and N-acetyl-glucosamine residues which showed a tendency to disappear in porcine cytomegalovirus infection and to increase in atrophic rhinitis, respectively.

Identification of serotypes of Haemophilus pleuropneumoniae by counterimmunoelectrophoresis

Counterimmunoelectrophoresis, direct immunofluorescence and immunodiffusion procedures were used to serotype 15 strains of Haemophilus pleuropneumoniae isolated from the respiratory tract of pigs in southern Brazil. Antigens were prepared by extracting cultures with a saline solution or by the phenol-water method. Antisera were prepared in rabbits against serotypes 1, 2, 3 and 5. Thirteen of the isolates were type 5 and two were type 3. No differences were observed between the results obtained in serotyping with counter immunoelectrophoresis and direct immunodiffusion, but both procedures were significantly better than immunodiffusion except with the saline extracted antigen. Counterimmunoelectrophoresis was quicker, more sensitive and more easily performed than the other techniques.

Comparison of complement fixation test and enzyme-linked immunosorbent assay for detection of early infection with Mycoplasma hyopneumoniae

The relative merits of the complement-fixation test (CF) and enzyme-linked immunosorbent assay (ELISA) for the detection of the early antibody response to Mycoplasma hyopneumoniae were evaluated. Discriminant analysis, a statistical procedure, was used to avoid difficulties associated with variation in background color and nonspecific reactions obtained with ELISA with different sera. Specific-pathogen-free pigs were exposed by contact to other specific-pathogen-free pigs which had been inoculated with M hyopneumoniae intratracheally (experiment A) or intranasally (experiment B) 18 to 21 days previously. Sera were collected from each pig before contact exposure and once a week until necropsy. Antibodies were detected by CF at postexposure (PE) week 3 in animals in experiment A (6 of 18) and at PE week 5 in experiment B (3 of 12). The ELISA antibodies were detected at 2 weeks after beginning of contact exposure in experiments A (4 of 18) and B (1 of 12). Examination of pooled data for experiments A and B indicated that ELISA was substantially (P less than 0.05) more sensitive for detection of antibodies than was the CF test at 3 to 5 weeks after contact exposure began. At PE weeks 6 and 7, both tests were similarly effective in detecting M hyopneumoniae antibodies.

Effect of age on susceptibility of pigs to Mycoplasma hyopneumoniae pneumonia

The effect of age on susceptibility of pigs to Mycoplasma hyopneumoniae was compared in 2 experiments. In experiment A, pigs 3, 6, and 12 weeks of age were contact-exposed to pigs with established M hyopneumoniae infection for 27 days and then evaluated for pneumonia at necropsy done at 42 days after exposure began. In experiment B, pigs 3 and 11 to 12 weeks of age were contact-exposed for 20 days and then placed in separate, isolated hog houses until necropsy was done at 49 days after exposure began. Evaluations at necropsies revealed that no differences existed between age groups concerning occurrence or severity of pneumonia. Likewise, immunofluorescence and culture evaluations of lung tissue revealed that no significant differences existed among age groups concerning detection of M hyopneumoniae or time of seroconversion to the organism. Under conditions of this study, no differences were detected in susceptibility of pigs between 3 and 12 weeks of age.