R-type
pyocins are high-molecular-weight
bacteriocins carried within the chromosomes of some bacterial species, such as Pseudomonas aeruginosa, and almost certainly evolved from lysogenic bacteriophages of the Myoviridae family. They contain no head structures and no
DNA and are used as defense systems, usually against other strains of the same bacterial species. They bind with their tail fibers to targeted bacterial surface molecules and then kill by inserting a core or needle that dissipates the bacterial membrane potential. Their mechanism of action, high bactericidal potency (one
pyocin particle can kill one bacterium), and focused spectrum suggest that R-type
pyocins could be developed as
antibacterial agents. In a lethal mouse
peritonitis model, submicrogram quantities of
pyocin prevent death from 90% lethal dose inocula of a
pyocin-sensitive, clinical isolate of P. aeruginosa. We show here the dose response curves, treatment windows, or periods of response after
infection and the several-log-unit acute reduction of bacterial load in blood and spleen samples, suggesting that R-type
pyocins have several characteristics that one would expect from an effective therapeutic.