Polymyxin B6 sulfate

Polymyxin B is a peptide antibiotic complex present as sulphate. The components were separated preparatively on a poly(styrene-divinylbenzene) (PLRP-S), 1000 A, 8 microm, 250 x 12.5 mm I.D. stationary phase maintained at 60 degrees C and using 215 nm detection. Elution was carried out with acetonitrile-sodium sulphate solution (0.7%, m/v; pH adjusted to 2.5 with trifluoroacetic acid)-water (18:50:32, v/v) at a flow-rate of 4.0 ml/min. Seven polymyxin B components were isolated and characterized using 1H and 13C NMR. The molecular masses were confirmed by mass spectrometry. The structures of two components were determined for the first time. Polymyxins B5 and B6 were identified as having the same composition as polymyxin B1 except that the fatty acid moiety was nonanoic acid and 3-hydroxy-6-methyloctanoic acid, respectively.

The toxicity of 6-mercaptopurine was potentiated by 2 mg of either Escherichia coli 026:B6 B endotoxin or Salmonella typhosa 0901 W endotoxin per kg. Nonlethal doses of heat-killed, gram-negative bacteria were also capable of potentiating the lethality of 6-mercaptopurine (6-MP). Salmonella minnesota S, the wild-type strain, and S. minnesota Re 595, a mutant containing only the lipid A and 2-keto-3-deoxyoctonate moiety of the endotoxin molecule, exhibited the same capability to enhance the toxic action of 6-MP. Endotoxin (lipopolysaccharide [LPS]) did not affect the clearance of 6-MP from the circulation, but did alter its apparent metabolism as indicated by blood levels of a metabolite, 6-thiouric acid. The concentration of blood urea nitrogen (BUN) in mice 18 h after injection of 100 mg of 6-MP per kg simultaneously with 2 mg of LPS per kg was significantly elevated over normal values. However, these BUN values were significantly less than those resulting from the administration of one mean lethal dose of either agent. The clearance from the circulation of the gram-negative organism E. coli HB, or the gram-positive organism Staphylococcus epidermidis S, was not affected by 6-MP. Endotoxin had no effect on the clearance of S. epidermidis S, but inhibited that of E. coli HB. When 6-MP and LPS were administered simultaneously with either bacterial species, only the clearance of E. coli HB was inhibited. Mice were protected from the lethality associated with combinations of 6-MP and LPS by (i) prior treatment with phenobarbital, (ii) caffeine, (iii) methylprednisolone, and (iv) polymyxin B sulfate. With the exception of caffeine, each regimen protected mice against the lethal effects of 400 mg of 6-MP per kg, and methylprednisolone or polymyxin B protected mice against 8 mg of LPS per kg.

Polymyxin-resistant (PBLr) mutants of Agrobacterium tumefaciens A6, B6, and B6M were isolated from polymyxin-sensitive (PBLs) parent strains in a defined medium containing 600 microgram of polymyxin B sulfate per millilitre. The weight and number of tumors induced by PBLr mutants on a variety of host plants such as carrot, potato, and pinto bean were 45--75% less than those induced by PBLs wild types. The crude cell envelopes (CCE) prepared from both PBLs and PBLr bacteria were inhibitory for tumor initiation when they were applied before or during the inoculation of viable tumorigenic bacteria, but not when they were applied 30 min after the inoculation of infectious bacteria. The potency to inhibit the tumor initiation by the CCE prepared from PBLs cells was approximately 50% higher than that by the equal amount of the CCE prepared from PBLr cells. The concentration of CCE preparations required to reduce tumor induction 50% in carrot and pinto bean was determined to be 2.6 mg/mL and 4.0--6.2 mg/mL for the CCE derived from PBLs and PBLr cells, respectively. These data suggest that the envelope structure or composition of PBLs and PBLr cells is distinct, and that the acquisition of resistance to polymyxin by agrobacteria modifies envelope structure or components which are essential for tumor initiation.