Synergism of microcin J25 with a membrane-permeabilizing peptide against microcin-resistant bacteria

MARíA FERNANDA POMARES; RICARDO FARíAS; RAúL SALOMóN; PAULA VINCENT

Rosario, Argentina

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular; 2006

Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular

Microcin J25 (MccJ25), a peptide antibiotic produced by Escherichia coli, is active on strains from Escherichia, Salmonella and Shigella species. Other gram negative bacteria such as clinical isolates of Enterobacter cloacae, Citrobacter freundii, Klebsiella pneumoniae and Salmonella typhimurium, are completely resistant. Entry of MccJ25 into susceptible cells is mediated by the outer membrane receptor FhuA, and the inner membrane proteins TonB, ExbB, ExbD, and SbmA. The aim of the present study was to determine whether the membrane-permeabilizing peptide (MPP) KFFKFFKFFK could sensitize microcin-resistant strains against the antibiotic. When MccJ25-resistant fhuA and sbmA mutants, as well as the above clinical isolates, were coincubated with MccJ25 and MPP (30 ìg/ml) they became sensitive to the antibiotic. MPP has no direct activity when used alone. Using the dye-probe DiSC3[5] we corroborated that MPP increases membrane permeability, and this could allow nonspecific (receptor-independent) entry of MccJ25 into the cells. Interestingly, we found that E. coli SBG231, a strain carrying an RNA polymerase mutation that makes it resistant to MccJ25, was also sensitized by MPP. This suggests that the antibiotic is acting on the membrane target. Our results could have implications for a potential therapeutic use of MccJ25.