Release of the periplasmic ribonuclease I into the medium from Escherichia coli treated with the membrane-active polypeptide antibiotic polymyxin B

Interaction of complement and polymyxin with gram-negative bacteria

The interaction of complement and polymyxin with gram-negative bacteria has been investigated by using three strains of Salmonella typhimurium in an attempt to determine the loci of complement action. It has been shown that the bactericidal activities of complement and polymyxin towards a smooth gram-negative organism are similarly affected by various components of the bactericidal test system. Further, complement and polymyxin have been shown to act synergistically in the bactericidal event. Evidence is presented which suggests that each agent produces lesions in the outer membrane of gram-negative bacteria, allowing lysozyme to interact with its glycopeptide substrate. An attack on the inner cytoplasmic membrane follows, since cell respiration is rapidly inhibited and this membrane becomes sufficiently disorganized to permit massive leakage of beta-galactosidase from the cytoplasm of the target cells.

Relation of beta-lactamase activity and cellular location to resistance of Enterobacter to penicillins and cephalosporins

The Enterobacter species E. aerogenes, E. cloacae, and E. hafnia were examined for resistance to penicillin and cephalosporin derivatives. All were resistant to benzyl penicillin, ampicillin, 6 [d(-)alpha-amino-p-hydroxyphenylacetamido] penicillanic acid, cephaloridine, cephalothin, and cephalexin. A significant number were sensitive to carbenicillin and 6 [d(-)alpha-carboxy-3-thienylacetamido] penicillanic acid. No differences among the three species were noted. The beta-lactamase activity was cell-bound, and was not released by osmotic shock, toluene treatment, or diphenylamine treatment. It was rarely released into the growth medium. The beta-lactamase activity was primarily directed against cephalosporin derivatives. Synthesis of beta-lactamase was chromosomally mediated. Resistance to ampicillin seemed to be partly related to entry of the molecule into the bacteria since exposure to ethylenediaminetetraacetate lowered the minimal inhibitory concentration.