No abstract

These results suggest that capuramycin analogues exhibit strong antimycobacterial potential and should be considered for further evaluation in the treatment of M. tuberculosis and M. avium-M. intracellulare complex infections in humans.

Acidic treatment of a mixture of caprazamycins (CPZs) A-G isolated from a screen of novel antimycobacterial agents gave caprazene, a core structure of CPZs, in high yield. Chemical modification of the resulting caprazene was performed to give its various derivatives. The structure-activity relationships of the caprazene derivatives against several mycobacterial species and pathogenic Gram-positive and Gram-negative bacteria were studied. Although caprazene showed no antibacterial activity, the antibacterial activity was restored for its 1'''-alkylamide, 1'''-anilide and 1'''-ester derivatives. Compounds 4b (CPZEN-45), 4d (CPZEN-48), 4f and 4g (CPZEN-51) exhibited more potent activities against Mycobacterium tuberculosis and M. avium complex strains than CPZ-B. These results suggest that caprazene would be a good precursor from which novel semisynthetic antibacterial antibiotics can be designed for the treatment of mycobacterial diseases such as tuberculosis and M. avium complex infection.

To gain a better understanding of the pathological role of interferon-y (IFN-y) in specific granuloma formation, IFN-y gene-deficient mice (BALB/c and C57BL/6) were produced. The IFN-y gene in embryonic stem (ES) cells was disrupted by inserting the P-galactosidase gene (IacZ) and the neomycin resistance gene ( m u ) at the translation initiation site in exon 1 by homologous recombination. Six-week-old IFN-y-deficient and wild-type mice were inoculated with lo3 -10' bacilli of various strains of Mycobacteriurn tuberculosis (Kurono, H37Rv, H37Ra and BCG Pasteur) through their tail veins. The mice were examined 7 weeks later for granuloma formation. The avirulent BCG Pasteur and H37Ra strains (lo3-lo4 bacilli/ml) induced granulomas in the spleen, liver and lungs of IFN-y-deficient mice. The granulomas consisted of epithelioid macrophages and Langhans multinucleate giant cells, but lacked caseous necrosis. The virulent Kurono and H37Rv strains induced disseminated abscesses but not granulomas in various organs of IFN-y-deficient mice and Mac-3-positive macrophages were not detected in the abscess lesions. These results suggest that IFN-y may be primarily responsible for macrophage activation and that other factor(s) may be involved in the granuloma formation mechanism.

bWe evaluated the antituberculosis (anti-TB) activity of five ␤-lactams alone or in combination with ␤-lactamase inhibitors against 41 clinical isolates of Mycobacterium tuberculosis, including multidrug-resistant and extensively drug-resistant strains. Of those, tebipenem, an oral carbapenem, showed the most potent anti-TB activity against clinical isolates, with a MIC range of 0.125 to 8 g/ml, which is achievable in the human blood. More importantly, in the presence of clavulanate, MIC values of tebipenem declined to 2 g/ml or less.

Drug-resistant tuberculosis (TB), which includes multidrug-resistant (MDR-TB), quinolone-resistant (QR-TB) and extensively drug-resistant tuberculosis (XDR-TB), is a serious threat to TB control. We aimed to characterize the genotypic diversity of drug-resistant TB clinical isolates collected in Thailand to establish whether the emergence of drug-resistant TB is attributable to transmitted resistance or acquired resistance. We constructed the first molecular phylogeny of MDR-TB (n=95), QR-TB (n=69) and XDR-TB (n=28) in Thailand based on spoligotyping and proposed 24-locus multilocus variable-number of tandem repeat analysis (MLVA). Clustering analysis was performed using the unweighted pair group method with arithmetic mean. Spoligotyping identified the Beijing strain (SIT1) as the most predominant genotype (n=139; 72.4%). The discriminatory power of 0.9235 Hunter-Gaston Discriminatory Index (HGDI) with the 15-locus variable-number tandem repeats of mycobacterial interspersed repetitive units typing was improved to a 0.9574 HGDI with proposed 24-locus MLVA, thereby resulting in the subdivision of a large cluster of Beijing strains (SIT1) into 17 subclusters. We identified the spread of drug-resistant TB clones caused by three different MLVA types in the Beijing strain (SIT1) and a specific clone of XDR-TB caused by a rare genotype, the Manu-ancestor strain (SIT523). Overall, 49.5% of all isolates were clustered. These findings suggest that a remarkable transmission of drug-resistant TB occurred in Thailand. The remaining 50% of drug-resistant TB isolates were unique genotypes, which may have arisen from the individual acquisition of drug resistance. Our results suggest that transmitted and acquired resistance have played an equal role in the emergence of drug-resistant TB. Further characterization of whole genome sequences of clonal strains could help to elucidate the mycobacterial genetic factors relevant for drug resistance, transmissibility and virulence.

DNA gyrase mutations are a major cause of quinolone resistance in Mycobacterium tuberculosis. We therefore conducted the first comprehensive study to determine the diversity of gyrase mutations in pre-extensively drug-resistant (pre-XDR) (n ‫؍‬ 71) and extensively drug-resistant (XDR) (n ‫؍‬ 30) Thai clinical tuberculosis (TB) isolates. All pre-XDR-TB and XDR-TB isolates carried at least one mutation within the quinolone resistance-determining region of GyrA ( . MIC and DNA gyrase supercoiling inhibition assays were performed to determine the role of gyrase mutations in quinolone resistance. Compared to the MICs against M. tuberculosis H37Rv, the levels of resistance to all quinolones tested in the isolates that carried GyrA-D94G or GyrB-N538D (8-to 32-fold increase) were significantly higher than those in isolates bearing GyrA-D94A or GyrA-A90V (2-to 8-fold increase) (P < 0.01). Intriguingly, GyrB-E540D led to a dramatic resistance to later-generation quinolones, including moxifloxacin, gatifloxacin, and sparfloxacin (8-to 16-fold increases in MICs and 8.3-to 11.2-fold increases in 50% inhibitory concentrations [IC 50 s]). However, GyrB-E540D caused low-level resistance to early-generation quinolones, including ofloxacin, levofloxacin, and ciprofloxacin (2-to 4-fold increases in MICs and 1.5-to 2.0-fold increases in IC 50 s). In the present study, DC159a was the most active antituberculosis agent and was little affected by the gyrase mutations described above. Our findings suggest that although they are rare, gyrB mutations have a notable role in quinolone resistance, which may provide clues to the molecular basis of estimating quinolone resistance levels for drug and dose selection.

The in vitro activities of DC-159a against seven species of Mycobacterium were compared with moxifloxacin, gatifloxacin, levofloxacin, and rifampin. DC-159a was the most active compound against quinolone-resistant multidrug-resistant M. tuberculosis (MIC 90 , 0.5 g/ml) as well as drug-susceptible isolates (MIC 90 , 0.06 g/ml). The anti-tubercle bacilli activity of DC-159a was 4-to 32-fold more potent than those of currently available quinolones. DC-159a also demonstrated the highest activities against clinically important nontuberculous mycobacteria.To be effective, tuberculosis (TB) treatment with a multidrug regimen must be continued for at least 6 months. This complicated regimen makes TB control difficult because of the long treatment duration, resulting in nonadherence of treatment, the development of multidrug-resistant TB (MDR-TB), and an additional problem of TB and human immunodeficiency virus (HIV) coinfection. Consequently, new anti-TB agents are urgently needed to overcome these problems (14).Quinolones such as ofloxacin and levofloxacin are classified and used as second-line drugs for MDR-TB cases because they inhibit the supercoiling action of DNA gyrase, which is different from the target enzymes of first-line drugs; however, their bactericidal activities against Mycobacterium tuberculosis are weak in clinical use (15). Currently, moxifloxacin and gatifloxacin, which are 8-methoxy fluoroquinolones, have proven to have more potent activities and may enable the duration of treatment to be shortened. Therefore, combination regimens consisting of new quinolones are expected to improve the treatment of TB (3,11,13). However, there is a problem of cross-resistance among quinolones caused by the previous usage of old quinolones in the treatment of MDR-TB and other respiratory infections. Thus, the emergence of quinolone-resistant M. tuberculosis is a concern (4).DC-159a is a newly synthesized broad-spectrum 8-methoxy fluoroquinolone. This compound has been shown previously to have potent activities against various respiratory pathogens, including quinolone-resistant strains (2, 7). The present study was performed to compare the in vitro antimycobacterial activities of DC-159a with three currently available quinolones and also rifampin against M. tuberculosis, including quinoloneresistant MDR (QR-MDR) strains and six species of clinically important nontuberculous mycobacteria (NTM).(This work was presented in part at the 46th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, September 2006.) Bacterial strains were isolated from Japanese patients between 1997 and 2003. The 32 M. tuberculosis isolates included drug-susceptible isolates (n ϭ 21) and QR-MDR isolates (n ϭ 11; levofloxacin MICs, Ն2 g/ml; rifampin MICs, Ն6 g/ml; isoniazid MICs, Ն4 g/ml). The NTM isolates comprised slowly growing mycobacteria, including M. kansasii (n ϭ 22), M. avium (serovar 4 [n ϭ 10] and serovar 8 [n ϭ 23]), and M. intracellulare serovar 16 (n ϭ 17), and rapidly growing mycobacteria, includin...