Induction of adaptive changes in the Streptococcus agalactiae transcriptome by human blood

In the present investigation, we conducted a bacterial transcriptome dynamics analysis during GBS incubation with human blood. We observed a large modification in the expression of genes involved in transcriptional regulation and in the metabolism of carbohydrates, purins/pyrimidins and inorganic ions, and an up-regulation of genes involved in attachment and plasminogen contact. We also observed differences in the expression of GBS genes in blood at 40° relative to 37°C. The serotype III GBS reference strain NEM316 was cultivated in Todd Hewitt broth supplemented with 0.2% yeast extract (THY) in 5% CO2 at 37°C until OD reached 0.7. Culture was harvested by centrifugation 8 minutes at 4000 x g at 37°C, then suspended in phosphate-buffered saline (PBS). Fresh heparinized human blood was obtained from seven healthy voluntary donors (four males and three females) in accordance with a protocol approved by the Institutional Review Board of the Methodist Hospital Research Institute. The blood was maintained at 37°C no more than one hour prior to use. Bacterial suspension was then incubated with the blood of each donor at 37°C and 40°C under slight rotation to avoid sedimentation of blood and bacterial cells (the volume of blood was equivalent to the volume of bacterial culture prior to centrifugation). Samples were removed for microarrays analysis immediately after adding bacteria, and after 30 and 90 minutes of incubation. Thus, for each of the seven blood donors, we obtained results for five time points: immediately after mixing the bacterium with the blood (time 0), after 30 minutes of contact with blood (time 1) at 37°C and 40°C, and after 90 minutes of contact with blood (time 2) at 37°C and 40°C.