Permeability of Pseudomonas aeruginosa outer membrane to hydrophilic solutes. (1/3)

Pseudomonas aeruginosa is usually resistant to a wide variety of antibacterial agents, and it has been inferred, on the basis of indirect evidence, that this was due to the low permeability of its outer membrane. We determined the permeability of P. aeruginosa outer membrane directly, by measuring the rates of hydrolysis of cephacetrile, cephaloridine, and various phosphate esters by hydrolytic enzymes located in the periplasm. The permeability to these compounds was about 100-fold lower than in the outer membrane of Escherichia coli K-12. Also, we found that the apparent Km values for active transport of various carbon and energy source compounds were typically higher than 20 microM in P. aeruginosa, in contrast to E. coli in which the values are usually lower than 5 microM. These results also are consistent with the notion that the P. aeruginosa outer membrane indeed has a low permeability to most hydrophilic compounds and that this membrane acts as a rate limiting step in active transport processes with high Vmax values.  (+info)

In vitro evaluation of pyridine-2-azo-p-dimethylaniline cephalosporin, a new diagnostic chromogenic reagent, and comparison with nitrocefin, cephacetrile, and other beta-lactam compounds. (2/3)

Pyridine-2-azo-p-dimethylanaline cephalosporin (PADAC), a chromogenic reagent which is purple and changes to yellow upon cleavage of its beta-lactam ring, was evaluated in comparison with other chromogenic cephalosporins. PADAC exhibited little antimicrobial activity against gram-negative bacteria, but did have good activity (minimum inhibitory concentration, 0.12 to 0.5 microgram/ml) against Staphylococcus aureus, a quality comparable to nitrocefin. Nitrocefin, however, demonstrated an unexpected and uniquely potent activity against Streptococcus faecalis (minimum inhibitory concentration, less than or equal to 0.06 to 0.12 microgram/ml) The relative hydrolysis rate of PADAC when subjected to six different beta-lactamases was substantially greater than that of cephacetrile, but less than that of nitrocefin. The relative hydrolysis rates of PADAC and nitrocefin were comparable with type IIIa beta lactamase and the derived from Bacillus cereus. The inhibition of beta-lactamase hydrolysis of the chromogenic cephalosporin substrates by six enzyme-stable inhibitors was generally greater with PADAC than with nitrocefin. Unlike nitrocefin, PADAC mixed with 50% human serum or various broth culture media showed no evidence of color change or degradation over several hours. The subsequent enzyme hydrolysis rates of such mixtures were the same as in phosphate buffer. Beta-lactamase-containing bacterial suspensions and clinical specimens containing such bacteria produced positive visual and spectrophotometric color changes when mixed with PADAC or nitrocefin. Although color changes occurred more slowly with PADAC than with nitrocefin, PADAC was not adversely influenced (non-enzyme-related color change) by the protein content of specimens. PADAC appears to be a promising alternative for beta-lactamase diagnostic testing in the clinical and research microbiology laboratory.  (+info)

Metabolic fate of cephacetrile after parenteral administration in rats and rabbits. (3/3)

1. The metabolic fate of 14C-cephacetrile was studied in rats and rabbits. The plasma level of intravenously injected cephacetrile decreased with half-lives of 17 and 22 minutes in rats and rabbits respectively, this decline being associated with a rapid appearance of the active metabolite, desacetylcephacetrile. Intramuscularly injected cephacetrile was rapidly absorbed by rats with a maximum plasma level at 20 minutes and a half-life of 16 minutes. Cephacetrile and desacetylcephacetrile did not enter erythrocytes. Cephacetrile was weakly bound to the plasma protein in the rat, rabbit and man. 2. Both in rats and rabbits, almost all of the injected radioactivity was excreted in the urine within 72 hours as the intact antibiotic and desacetylcephacetrile, only small amounts appearing in feces via bile. Neither the gamma-lactone of desacetyl-7-cyanacetamidocephalosporanic acid nor the violet-reddish pigment (CGP-695) produced from cephacetrile were detectable in the plasma or urine of the animals. 3. In rats given the labeled antibiotic intravenously, the radioactivity was widely distributed with concentrations being high in the kidney, plasma and liver, and lowest in the brain. The radioactivity crossed the rat placenta and appeared in the fetus. Radioactivity in these tissues disappeared as the plasma level declined. 4. During daily intramuscular injection of 14C-cephacetrile to rat, no significant changes were observed in the peak level of the plasma radioactivity or in the half-lives. In addition, dosing of the labeled antibiotic for 7 days caused no increase in tissue levels of radioactivity.  (+info)