A total of 105 isolates of Mycoplasma pneumoniae were evaluated for susceptibility to moxifloxacin, sparfloxacin, levofloxacin, and ciprofloxacin. Moxifloxacin, a newly synthesized compound, showed the greatest activity. The MICs and MBCs at which 50 and 90% of isolates were affected were 0.15 (MIC 50 and MBC 50 ) and 0.3 g/ml (MIC 90 and MBC 90 ) respectively. The results indicate that moxifloxacin might be promising an antimycoplasmal agent.Mycoplasma pneumoniae is the causative agent of upper respiratory tract infections and pneumonia in humans (6). Recently the efficacy of new quinolones has been demonstrated in vitro against various respiratory pathogens, including M. pneumoniae (2,4,11). In this report, we compared the in vitro activity of moxifloxacin, a new member of the fluoroquinolone group which has potent antimicrobial activities against grampositive and gram-negative bacteria (3, 9), with those of other fluoroquinolone as references against M. pneumoniae.A total of 105 strains of M. pneumoniae isolated from throat swabs from patients with pneumonia from 1986 (and earlier) to 2000 were used. These strains were subcultured fewer than five times in liquid medium and stored at Ϫ80°C until use. The antimicrobial agents used were moxifloxacin (Bay12-8039; Bayer Yakuhin Ltd.), sparfloxacin (SPFX; Dainippon Pharmaceutical Co., Ltd.) levofloxacin (LVFX; Daiichi Pharmaceutical Co., Ltd.), and ciprofloxacin (CPFX; Bayer Yakuhin Ltd.). The MICs and MBCs against each drug were determined by serial dilutions of the drugs in broth medium as described previously (5,8). Briefly, each strain of M. pneumoniae cultured for 5 days was diluted to 10 5 CFU/ml and 200 l of each sample was cultured in a sealed microtiter plate (Nunc Co., Ltd., Roskilde, Denmark) at 37°C. After 2 days of cultivation, twofold dilutions of the antimicrobial agents were added to samples of each strain. After an additional 2 days of cultivation, two and three 10-fold dilutions of each sample were used for plating on agar plates to provide a range of 500 to 1,000 CFU/10 l of the sample. The number of mycoplasmas in broth without drugs reached approximately 10 7 CFU/ml. MIC is defined as the lowest concentration of an antimcrobial agent inhibiting more than 99% of the mycoplasmal colonies with the control. The definition of MBC most often used in clinical microbiology is the lowest drug concentration that kills 99.9% of the bacterial population in a liquid medium.As shown in Fig. 1a, moxifloxacin (MIC for 50% of isolates [MIC 50 ], 0.15 g/ml; MIC for 90% of isolates [MIC 90 ], 0.3 g/ml) was more active than SPFX (MIC 50 , 0.3 g/ml; MIC 90 , 1.25 g/ml), LVFX (MIC 50 , 1.25 g/ml; MIC 90 , 2.5 g/ml), and CPFX (MIC 50 , 5.0 g/ml, MIC 90 , 5.0 g/ml). The MBCs and their distributions among the strains for these agents are shown in Fig. 1b; the MBCs of moxifloxacin (MBC 50 , 0.15 g/ml; MBC 90 , 0.3 g/ml) were markedly lower than those of SPFX (MBC 50 , 0.6 g/ml; MBC 90 , 2.5 g/ml), LVFX (MBC 50 , 2.5 g/ml; MBC 90 , 5.0 g/ml), and CPFX (MBC 50 , 5.0 g/m...

A component that binds to human lymphoid cells was isolated from the membranes of Acholeplasma laidlawii PG8. The component was extracted using the Bligh-Dyer method and purified using a silica-gel column and TLC.