Transcript profiling of Actinobacillus pleuropneumoniae in BALF

Actinobacillus pleuropneumoniae is the etiologic agent of contagious pleuropneumonia, an economically important disease of commercially reared swine throughout the world. To cause this disease, A. pleuropneumoniae must rapidly overcome porcine pulmonary innate immune defenses. Since bronchoalveolar fluid (BALF) contains many of the innate immune components found in the lung, we examined the gene expression of a virulent serovar 1 strain of A. pleuropneumoniae after exposure to concentrated BALF. This experiment was also carried out with a malT mutant of the same strain. Labelled cDNA synthetised from tester condition (namely wt BALF, mutant BHI and mutant BALF) was co-hybridized on the microarray with labelled cDNA from the control condition (wt BHI). Control was labelled with Cy3. At least four hybridizations were conducted for each sample combination type. Microarray analysis was carried out using the TM4 Suite of softwares (TIGR) and the SAM algorithm, using a false discovery rate (FDR) value of 0%. For the planktonic and adhesion experiments, Cy5 signal (test) was compared to Cy3 signal (control) in order to obtain a list of significant differentially expressed genes. In order to obtain the list of differentially expressed genes between planktonic growth and adhesion, log2 ratios were compared in TM4 also using the SAM algorithm.