The mutations in the quinolone-resistance determining regions (QRDR) of the gyrA, gyrB and grlA genes and in the norA gene from five clinical isolates of methicillin resistant Staphylococcus aureus (MRSA) were examined by DNA sequencing. The mutation from Ser84 to Leu in GyrA was associated with relatively high-level resistance to quinolones, whereas the mutation from Glu88 to Gly or Lys in GyrA was associated with low-level resistance to quinolones. Mutations of the grlA gene were observed at codon 80 (Ser80) or 84 (Glu84), independent of the mutations of gyrA. No mutations were observed in either the gyrB or norA genes.

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.

The formation of experimental bladder calculus was studied. The calculus was formed by the uptake of ethylene glycolwater (1%) and retaining the silk thread in rat bladder with high frequency. The components of the calculus were calcium oxalate and calcium phosphate from the results of the electron prove micro analysis (EPMA) and ion chromatography. On the 7th day after the beginning of experiment, Pseudomonas aeruginosa was inoculated to the rat bladder via the urethra. Seven days after the infection, P. aeruginosa adhered to the surface of the calculus such as an aspect of a biofilm. It was considered that this experimental model was useful to study the adherence of bacteria, biofilm formation and its chemotherapy by antibacterial agents.