Light inhibits rifampicin inactivation and reduces rifampicin resistance due to a cloned mycobacterial ADP-ribosylation gene

Antimicrobial susceptibility testing, drug resistance mechanisms, and therapy of infections with nontuberculous mycobacteria

Within the past 10 years, treatment and diagnostic guidelines for nontuberculous mycobacteria have been recommended by the American Thoracic Society (ATS) and the Infectious Diseases Society of America (IDSA). Moreover, the Clinical and Laboratory Standards Institute (CLSI) has published and recently (in 2011) updated recommendations including suggested antimicrobial and susceptibility breakpoints. The CLSI has also recommended the broth microdilution method as the gold standard for laboratories performing antimicrobial susceptibility testing of nontuberculous mycobacteria. This article reviews the laboratory, diagnostic, and treatment guidelines together with established and probable drug resistance mechanisms of the nontuberculous mycobacteria.

Mycobacterial subversion of chemotherapeutic reagents and host defense tactics: challenges in tuberculosis drug development

Recent worldwide emergence of multidrug-resistant and extensively drug-resistant tuberculosis is threatening to destabilize tuberculosis control programs and urging global attention to the development of alternative tuberculosis therapies. Major roadblocks limiting the development and effectiveness of new drugs to combat tuberculosis are the profound innate resistance of Mycobacterium tuberculosis to host defense mechanisms as well as its intrinsic tolerance to chemotherapeutic reagents. The triangle of interactions among the pathogen, the host responses, and the drugs used to cure the disease are critical for the outcome of tuberculosis. We must better understand this three-way interaction in order to develop drugs that are able to kill the bacillus in the most effective way and minimize the emergence of drug resistance. Here we review our recent understanding of the molecular basis underlying intrinsic antibiotic resistance and survival tactics of M. tuberculosis. This knowledge may help to reveal current targets for the development of novel antituberculosis drugs.

A rifampin-hypersensitive mutant reveals differences between strains of Mycobacterium smegmatis and presence of a novel transposon, IS1623

Rifampin is a front-line antibiotic for the treatment of tuberculosis. Infections caused by rifampin- and multidrug-resistant Mycobacterium tuberculosis strains are difficult to treat and contribute to a poor clinical outcome. Rifampin resistance most often results from mutations in rpoB. However, some drug-resistant strains have rpoB alleles that encode the phenotype for susceptibility. Similarly, non-M. tuberculosis mycobacteria exhibit higher levels of baseline resistance to rifampin, despite the presence of rpoB alleles that encode the phenotype for susceptibility. To identify other genes involved in rifampin resistance, we generated a library of Mycobacterium smegmatis mc(2)155 transposon insertion mutants. Upon screening this library, we identified one mutant that was hypersensitive to rifampin. The transposon insertion was localized to the arr gene, which encodes rifampin ADP ribosyltransferase, an enzyme able to inactivate rifampin. Sequence analysis revealed differences in the arr alleles of M. smegmatis strain mc(2)155 and previously described strain DSM 43756. The arr region of strain mc(2)155 contains a second, partial copy of the arr gene plus a novel insertion sequence, IS1623.