Anti-multidrug-resistant Acinetobacter baumannii activity of DS-8587: In vitro activity and in vivo efficacy in a murine calf muscle infection model.

DS-8587 is a novel broad-spectrum fluoroquinolone with extended antimicrobial activity against both Gram-positive and Gram-negative pathogens. In this study, we evaluated the in vitro and in vivo antibacterial activity of DS-8587 against multidrug-resistant (MDR) Acinetobacter baumannii. The MIC range of DS-8587 against MDR A. baumannii was 0.25-2 mg/L. These DS-8587 MICs were a minimum of 16-fold or 8-fold more potent than ciprofloxacin or levofloxacin, respectively. Bactericidal activity, a 3 log10 reduction from the initial bacterial counts, was observed within 2 h for 1593644 and 4 h for 1593684 after exposure to DS-8587. Therapeutic efficacy of DS-8587 in the murine calf muscle model was observed at 256 mg/kg. The analysis of the pharmacokinetic and pharmacodynamic index revealed that the AUC/MIC ratio showed the best correlation with efficacy. The total and free drug AUC/MIC value required for a static effect was 29.4 and 14.1, respectively. These data indicate DS-8587 would be an effective agent against MDR A. baumannii infection.

[Bactericidal effect of levofloxacin injection in combination with meropenem against Pseudomonas aeruginosa using an in vitro simulation model with a hollow fiber system].

An in vitro human plasma concentration simulation model with a hollow fiber system was established and used to evaluate the bactericidal effect of levofloxacin (LVFX) 500mg q.d. in combination with meropenem (MEPM) 1000mg t.i.d. against Pseudomonas aeruginosa. Six clinical isolates of P. aeruginosa which had MEPM MICs of 2 - 16 microg/mL, LVFX MICs of 2 microg/mL, and fractional inhibitory concentration (FIC) indices by the in vitro checkerboard method of 0.625-1 were used. In the treatment with MEPM alone, initial viable counts (10(6)-10(7) CFU/ mL) decreased, but did not reach below the detection limit (100 CFU/mL) and the regrowth of bacteria was observed. In the treatment with LVFX alone, viable counts decreased once below the detection limit, although increased after treatment for 24 hours. On the other hand, in the treatment with LVFX-MEPM combination, more potent bactericidal effects were observed compared to LVFX or MEPM alone in all strains. Especially, in the strains with MEPM MICs of 2 and 4 microg/mL, viable counts rapidly decreased below the detection limit and no regrowth was observed until 24 hours. These results suggested that LVFX-MEPM has a potential to be an effective combination against P. aeruginosa by synergistic rapid bactericidal action in clinical settings, even in the strain against which no significant synergy is confirmed by the traditional in vitro checkerboard method.

[Novel model of replicative Legionella pneumophila lung infection in DBA/2 mice].

We present here a new model of Legionella pneumophila lung infection in DBA/2 mice. By intranasal inoculation with 106 colony-forming units of L. pneumophila strain suzuki serogoup 1, persistent non-lethal lung infection was established as reflected by the detection of more than 10(4) CFU/lung of the organism 14 days after infection. Treatment of mice with cyclophosphamide before infection enhanced bacterial replication in the lungs and all cyclophosphamide-treated mice experienced lethal infection. Histopathologically, the course of non-lethal lung infection was characterized by early response of neutrophiles, then monocyte/macrophages response in the alveoli with disease progression, and diffuse alveolar wall thickening with lymphocyte migration at later phase of infection. Transmission electron microscopic evaluation of the lungs confirmed that L. pneumophila located intracellularly within neutrophiles and infrequently intracellular bacteria were observed undergoing binary fission. Therefore, the mouse model of replicative L. pneumophila lung infection provides method for evaluating pathogenesis of L. pneumophila lung infection and antibacterial therapy.

[Therapeutic efficacy of levofloxacin against a model of replicable Legionella pneumophila lung infection in DBA/2 mice].

The in vitro and in vivo antibacterial activities of levofloxacin (LVFX), a quinolone antibacterial, against clinically isolated Legionella pneumophila were investigated in comparison with those of existing antimicrobial agents approved for legionnaires disease. The minimum inhibitory concentrations (MICs) of the agents against 42 strains of L. pneumophila isolated in Japan were determined using agar dilution methods with buffered starch yeast extract agar. MIC90 of LVFX was 0.03 microg/ml and this activity was similar to ciprofloxacin and pazufloxacin, and higher than telithromycin and minocycline. Therapeutic efficacy of LVFX was studied against a pneumonia model induced by intranasal of L. pneumophila strain suzuki serogoup 1 in DBA/2 mice. Therapeutic doses in mice were selected that would closely match human exposure profile, area under the concentration-time curve (AUC) for a human oral dose of LVFX at 500 mg once a day. LVFX decreased significantly the bacterial burden in the lungs from the next day of commencing treatment. These results, including in vitro antibacterial activity against clinical isolates and therapeutic efficacy of a humanized dosing regimen, provide good evidence to support the use of LVFX at 500 mg once a day for treating patient with legionnaires disease.

In vitro and in vivo antibacterial activities of DC-159a, a new fluoroquinolone.

DC-159a is a new 8-methoxy fluoroquinolone that possesses a broad spectrum of antibacterial activity, with extended activity against gram-positive pathogens, especially streptococci and staphylococci from patients with community-acquired infections. DC-159a showed activity against Streptococcus spp. (MIC(90), 0.12 microg/ml) and inhibited the growth of 90% of levofloxacin-intermediate and -resistant strains at 1 microg/ml. The MIC 90s of DC-159a against Staphylococcus spp. were 0.5 microg/ml or less. Against quinolone- and methicillin-resistant Staphylococcus aureus strains, however, the MIC 90 of DC-159a was 8 microg/ml. DC-159a was the most active against Enterococcus spp. (MIC 90, 4 to 8 microg/ml) and was more active than the marketed fluoroquinolones, such as levofloxacin, ciprofloxacin, and moxifloxacin. The MIC 90s of DC-159a against Haemophilus influenzae, Moraxella catarrhalis, and Klebsiella pneumoniae were 0.015, 0.06, and 0.25 microg/ml, respectively. The activity of DC-159a against Mycoplasma pneumoniae was eightfold more potent than that of levofloxacin. The MICs of DC-159a against Chlamydophila pneumoniae were comparable to those of moxifloxacin, and DC-159a was more potent than levofloxacin. The MIC 90s of DC-159a against Peptostreptococcus spp., Clostridium difficile, and Bacteroides fragilis were 0.5, 4, and 2 microg/ml, respectively; and among the quinolones tested it showed the highest level of activity against anaerobic organisms. DC-159a demonstrated rapid bactericidal activity against quinolone-resistant Streptococcus pneumoniae strains both in vitro and in vivo. In vitro, DC-159a showed faster killing than moxifloxacin and garenoxacin. The bactericidal activity of DC-159a in a murine muscle infection model was revealed to be superior to that of moxifloxacin. These activities carried over to the in vivo efficacy in the murine pneumonia model, in which treatment with DC-159a led to bactericidal activity superior to those of the other agents tested.