apidaecin-ib and Klebsiella-Infections

The peptides Api88 and Onc72 are highly efficient to treat Escherichia coli bacteremia in mice. Here we extended the animal studies to a systemic murine infection model using a multidrug-resistant carbapenemase-producing Klebsiella pneumoniae clinical isolate. When administered intraperitoneally three times at 2.5, 5 and 10 mg/kg bodyweight to CD-1 mice infected with a KPC-producing K. pneumoniae strain, both Api88 and Onc72 reduced the bacterial counts by at least 5 log₁₀ units, indicating that both peptides are active in vivo. Both peptide treatments increased significantly the survival rates and average survival times compared to untreated animals for all doses except for the highest dose of Onc72. This dose reduced the bacterial counts so fast that it most likely induced a sudden release of large amounts of toxic materials from the killed bacteria reducing the survival time even below that of untreated mice. In conclusion, both peptides were efficient in the lethal murine K. pneumoniae infection model, but the treatment protocol (i.e. dose and time points) has to be further optimized based on future pharmacokinetic studies.

Topics: Amino Acid Sequence; Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Bacterial Proteins; beta-Lactamases; Drug Resistance, Multiple, Bacterial; Female; Klebsiella Infections; Klebsiella pneumoniae; Mice; Molecular Sequence Data

Proline-rich antimicrobial peptides (PrAMPs) freely penetrate through the outer membrane into the periplasm of Gram-negative bacteria, before they are actively translocated by a permease/transporter-mediated uptake into the cytoplasm where they are reported to inhibit chaperone DnaK. Here we have studied the PrAMP apidaecin 1b, which is produced in honey bees in response to bacterial infections, and optimized apidaecin analogs for their bacterial uptake. The peptides were labeled with 5(6)-carboxyfluorescein and their internalization in Escherichia coli and Klebsiella pneumoniae was visualized by fluorescence microscopy and quantified by flow cytometry for four different time points over an incubation period of 4 h. Apidaecin 1b entered only 40% to 50% of the cells at detectable quantities, whereas designer peptides Api88, Api134 and Api155 entered more than 95% of the bacteria within 30 min at around fourfold higher quantities than the native peptide. Interestingly, a shortened version designated as (1-17)Api88, bound DnaK as efficiently as the 18-residue long Api88 and entered the bacteria at similar kinetics as Api88, but was unable to inhibit the bacterial growth. Similar conflicts with currently proposed mechanisms of PrAMPs were also obtained for some Ala-substituted analogs and reverse apidaecin sequences. Although peptides with C-terminal amides enter the cells much more efficiently than homologous C-terminal acids, this improved cell penetration does not improve the antibacterial activities. These studies suggest that PrAMPs utilize additional modes of action to kill sensitive organisms.

Topics: Amino Acid Sequence; Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Escherichia coli; Escherichia coli Infections; Humans; Klebsiella Infections; Klebsiella pneumoniae; Molecular Sequence Data; Proline