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. Author manuscript; available in PMC: 2013 Sep 1.
Published in final edited form as: Mol Microbiol. 2012 Jul 26;85(6):1119–1132. doi: 10.1111/j.1365-2958.2012.08163.x

Figure 5. High sub-lethal challenge with polymyxin B inhibits secretion of SpeB and SLO, but not SIC.

Figure 5

Expression of the SpeB protease in cultures of S. pyogenes SF370 was determined following challenge with the indicated concentrations of polymyxin B by quantitation of cysteine protease activity in culture supernatant (A), by real-time RT-PCR analysis of speB transcript abundance (A, inset) by Western blot analysis of culture supernatant (B) in whole cell lysates (C) and following overnight culture on protease indicator plates containing (+) or lacking (−) 150 μM polymyxin B (D). Expression of SpeB results in a zone of clearing around colonies. Western blotting was also used to analyze the amount of SLO (E) and SIC (F) present in culture supernatant following challenge with the indicated concentrations of polymyxin B. All samples for SpeB analysis were harvested at 3 hrs post-challenge; samples for SLO and SIC were harvested 2hrs post-challenge. Open and filled triangles indicate the migration of the zymogen and mature form of SpeB, respectively. The migration of the SLO and SIC polypeptides are also indicated.