Induction of Mycobacterial Resistance to Quinolone Class Antimicrobials

ABSTRACTAn agar plate assay was developed for detecting the induction of drug-resistant mycobacterial mutants during exposure to inhibitors of DNA gyrase. WhenMycobacterium smegmatison drug-containing agar, resistant colonies arose over a period of 2 weeks. ArecAdeficiency reduced mutant recovery, consistent with involvement of the SOS response in mutant induction. The C-8-methoxy compounds gatifloxacin and moxifloxacin allowed the recovery of fewer resistant mutants than either ciprofloxacin or levofloxacin when present at the same multiple of the MIC; a quinolone-like 8-methoxy-quinazoline-2,4-dione was more effective at restricting the emergence of resistant mutants than its cognate fluoroquinolone. Thus, the structure of fluoroquinolone-like compounds affects mutant recovery. A spontaneous mutator mutant ofM. smegmatis, obtained by growth in medium containing both isoniazid and rifampin, increased mutant induction during exposure to ciprofloxacin. Moreover, the mutator increased the size of spontaneous resistant mutant subpopulations, as detected by population analysis. Induction of ciprofloxacin resistance was also observed withMycobacterium tuberculosisH37Rv. When measured with clinical isolates, no difference in mutant recovery was observed between multidrug-resistant (MDR) and pansusceptible isolates. This finding is consistent with at least some MDR isolates ofM. tuberculosislacking mutators detectable by the agar plate assay. Collectively, the data indicate that the use of fluoroquinolones against tuberculosis may induce resistance and that the choice of quinolone may be important for restricting the recovery of induced mutants.

Seymour Benzer. 15 October 1921 — 30 November 2007

Seymour Benzer was born in New York City in 1921. His parents were immigrants who had come to the United States some 10 years earlier from the Jewish shtetl of Sochaczew near Warsaw. A true scientific romantic, Benzer was a pioneer in two different fields of biology: the initial studies of the nature of the gene in the early days of molecular biology, and later the launching of a new field that applied mutant induction and other genetic approaches to the study of behaviour. In the century that began with the rediscovery of Mendelian units of heredity and ended with the sequencing of the human genome, Benzer's work set two milestones. His early work in bacteriophages on the fine structure of the gene defined a pivotal moment in the transition from classical to molecular genetics. His later work in the fruitfly, Drosophila melanogaster , launched an entirely new genetic strategy with which to tackle the complexity of behaviour.

RNA Interference Mutant Induction In Vivo Demonstrates the Essential Nature of Trypanosome Flagellar Function during Mammalian Infection

ABSTRACT We demonstrate that trypanosomes compromised in flagellar function are rapidly cleared from infected mice. Analysis of the PFR2 bloodstream RNA interference mutant revealed that defective cell motility occurred prior to cytokinesis failure. This validation provides a paradigm for the flagellum as a target for future assays and interventions against this human pathogen.

Expression of YAP4 in Saccharomyces cerevisiae under osmotic stress

YAP4, a member of the yeast activator protein (YAP) gene family, is induced in response to osmotic shock in the yeast Saccharomyces cerevisiae. The null mutant displays mild and moderate growth sensitivity at 0.4 M and 0.8 M NaCl respectively, a fact that led us to analyse YAP4 mRNA levels in the hog1 (high osmolarity glycerol) mutant. The data obtained show a complete abolition of YAP4 gene expression in this mutant, placing YAP4 under the HOG response pathway. YAP4 overexpression not only suppresses the osmosensitivity phenotype of the yap4 mutant but also relieves that of the hog1 mutant. Induction, under the conditions tested so far, requires the presence of the transcription factor Msn2p, but not of Msn4p, as YAP4 mRNA levels are depleted by at least 75% in the msn2 mutant. This result was further substantiated by the fact that full YAP4 induction requires the two more proximal stress response elements. Furthermore we find that GCY1, encoding a putative glycerol dehydrogenase, GPP2, encoding a NAD-dependent glycerol-3-phosphate phosphatase, and DCS2, a homologue to a decapping enzyme, have decreased mRNA levels in the yap4-deleted strain. Our data point to a possible, as yet not entirely understood, role of the YAP4 in osmotic stress response.