A PCR assay used to study aerosol transmission of Actinobacillus pleuropneumoniae from samples of live pigs under experimental conditions.

The study describes a polymerase chain reaction (PCR) assay for the detection of Actinobacillus pleuropneumoniae. The test is based on the amplification of the omlA gene coding for an outer membrane protein of A. pleuropneumoniae. To test the specificity of the reaction, 19 other bacterial species related to A. pleuropneumoniae or isolated from pigs were assayed. They were all found negative in the PCR assay. The detection threshold of the test was 10(2) A. pleuropneumoniae CFU/assay. The test was then applied to the detection of A. pleuropneumoniae from tonsillar biopsies and tracheobronchial lavage fluids of pigs without a culture step. The detection of A. pleuropneumoniae in these samples was performed by PCR, by conventional culture and by bacteriology with immunomagnetic beads. The number of samples that were found positive by PCR was almost three times higher than the number of samples from which A. pleuropneumoniae was isolated by both bacteriological techniques. The detection of A. pleuropneumoniae in these samples allowed us to demonstrate its aerosol transmission to pigs under experimental conditions. The trial involved 18 specific pathogen free pigs. Six pigs, infected with A. pleuropneumoniae, were located in a unit A, together with four non-infected animals (contact pigs). Eight non-infected pigs (reporter pigs) were located in a unit B, adjacent to A. We detected A. pleuropneumoniae in samples from infected animals but also from 'contact' (unit A) and 'reporter' (unit B) pigs. The results of this study show that the simple preparation of the samples followed by the PCR assay may be a useful tool for epidemiological studies.