Pacidamycin 3

A novel class of antibiotics was isolated from cultures of Streptomyces coeruleorubidus strain AB 1183F-64. The antimicrobial activity of the pacidamycins is selective against Pseudomonas aeruginosa. The various congeners are nucleoside peptides which differ in the terminal amino acid residues. The structures were determined using MS-MS and 2D NMR techniques.

Pacidamycins are nucleosidyl-peptide antibiotics which have activity only against Pseudomonas aeruginosa. Their MICs for other organisms such as Enterobacteriaceae, Staphylococcus aureus, most Streptococci and other Pseudomonas species are greater than 100 micrograms/ml. These compounds had no activity against erythromycin-susceptible Streptococci. The MICs for Streptococcus pyogenes with constitutive- and inducible-type of macrolide-lincosamide-streptogramin resistance were 12.5 and 25 micrograms/ml, respectively. The MICs against P. aeruginosa ranged from 8 to 64 micrograms/ml. The activity of these compounds was 1 to 2-fold less in serum than broth. Time-kill curves were performed using 4 and 8 times the MIC of pacidamycin 1. It was bactericidal against P. aeruginosa (3 log10 decrease in 4 to 6 hours). At 24 hours, resistant mutants were found in the cultures. The MICs of piperacillin and gentamicin for these mutants were the same as for the parent strain. The frequency of resistance to these compounds was less than 3.5 x 10(-6). The resistant mutants were stable after 10 transfers in antibiotic-free medium. The pacidamycins were inactive against P. aeruginosa in mouse protection test. After a single subcutaneous injection of 25 mg/kg of pacidamycin 1, the Cmax was approximately 50 micrograms/ml and the serum half-life was 0.5 hour.

The pacidamycins are a new complex of nucleosidyl-peptide antibiotics with highly specific activity against Pseudomonas aeruginosa. They are produced by Streptomyces coeruleorubidus AB 1183F-64 which was isolated from a soil sample collected at Offenburg in the FRG. The mature spore masses of the producing organism are greenish gray to blue, and the spore chains are arranged in spirals. After the structures of the pacidamycins were determined, the fermentation medium was supplemented with component amino acids. This resulted in the directed biosynthesis of several members of the complex. The overall antibiotic recovered was increased from 1 approximately 2 mg/liter to more than 100 mg/liter through a combination of strain selection, medium manipulation and amino acid feeding experiments.