Antimicrobial action of histone H1

Recently, the emergence of multi-drug resistant bacterial strains has become an increased health-care problem of pandemic proportions. There is a clear need for new and more effective therapeutics that can also be used in antibiotic-resistant bacteria. This project focuses on the antimicrobial effects of H1 in several bacterial strains and attempts to suggest a mechanism through which H1 might exert its antimicrobial properties.;Activity of H1, isolated from calf thymus with a purity of >99%, was tested against early to mid-log phase bacterial cultures utilizing the standard colony formation assay. The interaction of H1 with the LPS component of the outer membrane was investigated by studying the changes in H1 toxicity using the ionic interactions of magnesium and calcium (the 2 predominant divalent cations found on the LPS) with LPS. The ability of H1 to displace polymyxin (known to interact strongly with the LPS) off purified LPS was studied. Changes in sensitivity to H1 of Salmonella typhimurium lipid A mutants was also examined. The potential changes in membrane permeabilization were studied utilizing the synergistic effects of H1 with lysozyme and through the use of a flow cytometer and spectrofluorometer to measure the uptake of different fluorescent probes.;H1 proved to be highly effective in killing numerous bacterial strains. The effect of H1 were dose- and time-dependent. Maximal toxicity was achieved within a 10-minute, incubation time. H1 demonstrated a strong affinity to the LPS component, specifically the lipid A, of the outer membrane of the gram-negative organisms. Flow cytometric, and fluorometric analysis further showed that H1 causes a rapid loss of membrane integrity, which was proportional to cell killing.;In summary, H1 proved a potent antibiotic for numerous bacteria including gram-negative strains, having cytotoxic rather than cytostatic effect. The mechanism by which H1 exerts its bacteria-killing properties involves several steps. First is the high-affinity binding of H1 to the lipid A component of the bacterial cell membrane. Second by the incorporation of H1 into the membrane, through the interaction with phosphotidylglyocerol and cardiolipin, that leads to irreversible disruption of the membrane integrity and subsequent death.