Plasmid RP1-mediated susceptibility of Acinetobacter calcoaceticus to rat polymorphonuclear leukocyte granule contents.

The resistance plasmid RP1 was transferred by conjugation to a plasmidless strain of Acinetobacter calcoaceticus. Acquisition and expression of RP1 by A. calcoaceticus HO1-N was associated with an increase in sensitivity to the antimicrobial activity of extracted contents from rat polymorphonuclear leukocyte granules. Plasmid RP1-associated antibiotic resistance and sensitivity to granule contents were cured by exposure to acridine orange. Assays with granule extract fractions separated by fast protein liquid chromatography showed myeloperoxidase, protease, and lysozyme fractions to possess little or no antimicrobial activity against the A. calcoaceticus strains. A protein fraction designated peak D, containing two low-molecular-weight cationic peptides (M. J. Loeffelholz and M. C. Modrzakowski, Anal. Biochem., in press), did possess antimicrobial activity against both HO1-N and Ho1-N(RP1) strains, with the HO1-N(RP1) strain being significantly more sensitive.