Figure 7.

Serum influences the production of the PAO1 QS-controlled virulence factors, LasB, LasA, and phospholipase C. (A) At late phase of growth, serum enhances LasB production. PAO1 was streaked on elastin agar (EA) or elastin agar with 10% serum (EA/S). The plates were incubated at 37°C for 24 h and then at room temperature for 48 h before examination. Images are representative of three independent experiments. (B) Serum represses LasA production at early phase. PAO1 was grown in either LB or LB/S and samples were collected at the early phase. The supernatant fractions were isolated and the level of LasA activity in each fraction was determined using the staphylolytic assay as described in Experimental Procedures. (C) In the presence of serum, PAO1 produced increased levels of phospholipase C activity at late phase. Cells were grown as described in (B). Samples were collected at early and late phases, the supernatant fractions were isolated, and the level of phospholipase C activity in each fraction was determined as described in Experimental Procedures. For (B) and (C), values represent the means of three independent experiments ± SEM; ***P < 0.001.