The new thiolactone antibiotic, thiolactomycin, is rapidly absorbed in rats when administered either orally or by intramuscular injection. A peak in concentration of the drug is reached in the blood and in various visceral organs within 15 minutes after administration. The concentration decreases rather rapidly and about 51-69 % of the drug is excreted in urine during the first 24 hours.Though the in vitro effect of thiolactomycin is moderate, it effectively protected mice challenged intraperitoneally with several strains of S. marcescens and K. pneumoniae and was more effective than carbenicillin in treating experimental acute urinary tracts infected with S. marcescens.Also, in mice whose immunodefense was decreased by treatment with cyclophosphamide, thiolactomycin was more effective than carbenicillin against S. marcescens challenge.

No abstract

Escherichia coli easily developed resistance to a new antimicrobial agent of the sideromycin group, No. 216, by spontaneous mutation. Most of the No. 216-resistant mutants tested proved not to be cross-resistant to E. coli phages TI, T5, and tj?80. On the other hand, these phage-resistant mutants were cross resistant to No. 216. The initial site for binding of No. 216 to the sensitive cells was located, at the ton A gene product (Ton A-protein) of the outer membrane. However, unlike the phage-resistant mutants, ton A protein (78K-protein) in most No. 216-resistant mutants was intact and these mutants were possessed a particular 87K protein in the outer membrane. It is suggested that No. 216 is taken up by ton A protein and then penetrates into the cell by way of a particular transport system and that a highly mutable portion may exist in this reaction system.