Characteristics of quinolone-induced small colony variants in Staphylococcus aureus.

Exposure of Staphylococcus aureus to 1 x MIC of the quinolone antibiotic pazufloxacin for 24 h, followed by plating on drug-free media, led to the emergence of small colony variants (SCVs) in addition to large colony variants (LCVs). However, following incubation with 0.25 or 4 x MIC of pazufloxacin, only LCVs were obtained. The SCVs were half as susceptible to pazufloxacin or ciprofloxacin as wild-type S. aureus, while the susceptibilities of LCVs were essentially unchanged. The reduced susceptibilities of SCVs did not result from mutations in the quinolone-resistance-determining regions of DNA gyrase and topoisomerase IV, since the sequences of these genes were identical to those of the wild-type. However, the SCVs accumulated pazufloxacin and ciprofloxacin to a lesser degree than did wild-type. Furthermore, their susceptibility to quinolones was almost unaffected by reserpine or verapamil, suggesting that the reduced uptake resulted from decreased permeability, rather than from an active efflux pump. The ability of various quinolones to induce emergence of SCVs in S. aureus, correlated with the presence of carbon-bonded substituents at the C-7 position of a quinoline or naphthyridine nucleus, or with the presence of a benzoxazine nucleus. In conclusion, pazufloxacin-induced SCVs represent a mutant that one might expect to be rapidly eliminated in vivo and, hence, not to survive as a quinolone-resistant pathogen. This finding suggests a novel approach for development of future quinolones.

[Microbiological assay method for T-3761 concentration in body fluids].

A microbiological assay method for measurement of T-3761 and its stability in body fluids were investigated. The paper disc method proved suitable for this assay using Escherichia coli Kp as a test organism and commercially available heart infusion agar as a test medium. When using the paper disc method, lower detection limit of T-3761 was approximately 0.05 microgram/ml and 0.1 microgram/ml for 1/15M phosphate buffer (pH 7.0) and human serum, respectively. T-3761 in human serum and urine was stable under freezing -20 degrees C for at least 28 days.

[Absorption, distribution, metabolism and excretion of T-3761, a new quinolone derivative, in experimental animals].

We studied the absorption, distribution, metabolism and excretion of T-3761, a new quinolone derivative, in experimental animals. The following results were obtained. 1. The peak serum levels of T-3761 after a single oral administration to various fasting animals at a dose of 5 mg/kg were high in the order of rats, dogs, mice and rabbits, showing favorable absorption in all animals except for rabbits. In mice and rats, T-3761 showed higher peak serum levels than ofloxacin and ciprofloxacin but T-3761 were more rapidly eliminated from serum than ofloxacin and ciprofloxacin. 2. Tissue concentrations of T-3761 in rats were similar to those of ofloxacin but its ratio of tissue to serum levels were lower than those of ofloxacin. 3. Urinary excretion of T-3761 as active form until 24 hours after oral administration was 27.3%, 63.1%, 41.0% and 63.3% in mice, rats, rabbits and dogs, respectively. Only unchanged T-3761 was detected as active form in urine of all animals tested. In rats, urinary concentrations until 2 hours after administration were higher than those of ofloxacin. 4. Biliary excretion of T-3761 in mice and rats were 2.9% and 1.4% as active form. 5. The absorption of T-3761 was not different in male and female rats or 8 and 14 weeks old rats. The meal lowered absorption of T-3761 in rats. There was no significant difference in serum levels, urinary excretion and distribution to tissues after multiple administration of T-3761 comparing with its single administration. 6. In rats with liver dysfunction induced by D-galactosamine, the serum levels and urinary excretion were slightly higher than in normal rats. On the other hands, in rats with kidney dysfunction induced by HgCl2, the serum levels were significantly higher and urinary excretion of T-3761 was significantly lower than in normal rats. Above results show that T-3761 has unique characteristics in absorption, excretion and distribution after oral administration to animals among new quinolones, i.e., T-3761 was eliminated rapidly and poorly distributed to tissues but showed superior absorption and high peak serum levels.