Structure-activity relationships in a series of piperazine-2,3-dione containing penicillins and cephalosporins. II. Derivatives substituted at N(4) of the piperazine ring

Iron transport-mediated antibacterial activity of and development of resistance to hydroxamate and catechol siderophore-carbacephalosporin conjugates

Peptides containing residues of N5-acetyl-N5-hydroxy-L-ornithine were evaluated as potential artificial siderophores of beta-lactam-hypersusceptible Escherichia coli X580. Only those peptides which were capable of forming a hexadentate complex around ferric iron, which is analogous to the natural siderophore ferrichrome, were able to reverse the growth inhibition effects of the ferric iron chelator ethylenediamine di(o-hydroxyphenylacetic acid). A synthetic bis(catechol) spermidine derivative, similar to the natural siderophores enterobactin and agrobactin, also exhibited siderophore activity with this strain. Conjugation of the N5-acetyl-N5-hydroxy-L-ornithine tripeptide and the bis(catechol) siderophore to the potent carbacephalosporin loracarbef and closely related analogs provided compounds which exhibited antibacterial activity against E. coli X580. As was observed with the naturally occurring albomycins, the initial bactericidal effect was followed by the appearance of survivors that were resistant to the test compound. An enhanced killing effect was observed when the parent was incubated simultaneously with hydroxamate and catechol siderophore-antibiotic conjugates. Natural and synthetic siderophore growth promotion experiments with survivors resistant to the conjugates strongly suggested that disabled ferrichrome and enterobactin-catechol assimilation mechanisms may be responsible for the observed resistance. One isolated survivor was postulated to be a tonB mutant. The antibacterial activities of the described siderophore-carbacephalosporin conjugates appear to be related to an iron transport assimilation mechanism and would not have been detected during routine MIC testing procedures.

In vitro and in vivo evaluation of Ro 09-1428, a new parenteral cephalosporin with high antipseudomonal activity

Ro 09-1428, a new parenteral cephalosporin with a catechol moiety attached at position 7 of the cephalosporin ring, showed high in vitro activity against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, and Streptococcus pyogenes, with MICs for 90% of strains tested (MIC90s) of less than or equal to 0.39 micrograms/ml. Morganella morganii, Providencia rettgeri, Citrobacter freundii, Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pneumoniae were inhibited with MIC90s of less than or equal to 3.13 micrograms/ml. Serratia marcescens was less susceptible to Ro 09-1428, with a MIC90 of 25 micrograms/ml. The most distinctive feature of Ro 09-1428 was its potent activity against Pseudomonas aeruginosa and Acinetobacter calcoaceticus, with MIC90s of 0.39 and 6.25 micrograms/ml, respectively. Most of the ceftazidime-resistant strains of P. aeruginosa, E. cloacae, and C. freundii were inhibited by Ro 09-1428, while those of S. marcescens were resistant at a concentration of 12.5 micrograms/ml. Ro 09-1428 was more active than ceftazidime against staphylococci. PBP 3 was the most sensitive target in E. coli and P. aeruginosa. The response to ferric iron in growth medium suggests that Ro 09-1428 may be taken up by transport mechanisms similar to those of other catechol cephalosporins. In accordance with its in vitro activity, Ro 09-1428 activity was equal to or greater than ceftazidime activity in efficacy against experimental septicemias in mice. The results indicate that Ro 09-1428 is a broad-spectrum cephalosporin with advantages over ceftazidime in its activity against P. aeruginosa, staphylococci, and ceftazidime-resistant strains of C. freundii and E. cloacae.