Mechanisms of action on Escherichia coli of cecropin P1 and PR-39, two antibacterial peptides from pig intestine

Cecropin P1 and PR-39 are two antibacterial peptides isolated from the upper part of the small intestine of the pig. They have been sequenced, and their antibacterial spectra have been investigated (J.-Y. Lee, A. Boman, C. Sun, M. Andersson, H. Jörnvall, V. Mutt, and H. G. Boman, Proc. Natl. Acad. Sci. USA 86:9159-9162, 1989; B. Agerberth, J.-Y. Lee, T. Bergman, M. Carlquist, H. G. Boman, V. Mutt, and H. Jörnvall, Eur. J. Biochem. 202:849-854, 1991). We have now compared these two peptides for their mechanism of action on Escherichia coli K-12 by using three strains with different markers. Our results show that cecropin P1, like other cecropins, kills bacteria by lysis and that this reaction requires more peptide to kill more cells. PR-39 requires a lag period of about 8 min to penetrate the outer membrane of wild-type E. coli; then killing is quite fast. This lag period was absent in the envA1 mutant; in this strain the outer membrane was freely permeable to both peptides. PR-39 killed growing bacteria faster than nongrowing cells; for cecropin P1 there was no such difference. It is suggested from isotope incorporation experiments that PR-39 kills bacteria by a mechanism that stops protein and DNA synthesis and results in degradation of these components.