AM-7359--a novel oxazolidinone with low resistance potential and potent activity against drug resistant pathogens.

AM-7359 is a member of a novel series of oxazolidinones with antimicrobial activity against pathogens resistant to multiple antibiotics. Potent antibiotics with limited drug cross resistance to current therapeutic agents are needed for the treatment of drug resistant pathogens. This study investigated the resistance development to linezolid (LZD) and AM-7359 by key pathogens and the degree of cross resistance between these two oxazolidinones. Both AM-7359 and LZD, demonstrates a low frequency of resistance development. After 30 passages and selection for resistant development of four different Staphylococcus aureus and Enterococus faecium strains the minimum inhibitory concentration (MIC) for AM-7359 was 1

High-yield expression, purification, and characterization of active, soluble Bacteroides fragilis metallo-beta-lactamase, CcrA.

The gene from Bacteroides fragilis encoding a metallo-beta-lactamase, ccrA, was expressed in Escherichia coli BL21(DE3) containing the wild-type disulfide bond-catalyzing system dsb as an active, soluble enzyme in quantities exceeding 100 mg/liter using both rich and minimal media. Both the nonfusion and a glutathione S-transferase fusion enzyme lacking the periplasmic signal sequence were purified to homogeneity. Characteristics of the purified nonfusion enzyme are shown to be similar to those of the renatured enzyme previously reported. Thermal denaturation studies using circular dichroism and fluorescence spectroscopy show that CcrA undergoes a transition at approximately 50 degrees C which corresponds to the transition temperature of catalytic activity. The secondary structure of the protein and the catalytic apparatus are thus intimately linked.

Novobiocin-dependent topA deletion mutants of Escherichia coli.

Previous reports of the transduction of topA deletions in Escherichia coli suggested that delta top A transductants grow normally only if they acquire spontaneous mutations that compensate for the topoisomerase I defect. We show that P1-mediated transduction of delta topA in the presence of sublethal concentrations of novobiocin, an inhibitor of the DNA gyrase B subunit, yields uncompensated Top- isolates which are dependent on novobiocin for optimum growth. In the absence of novobiocin these delta topA strains grow slowly, indicating that topA deletions are deleterious but not lethal to the cell. We propose that inhibitors of DNA gyrase B, presumably by lowering intracellular levels of DNA supercoiling, can phenotypically suppress a topoisomerase I defect in E. coli.

Role of the supX gene in ultraviolet light-induced mutagenesis in Salmonella typhimurium.

Salmonella typhimurium strains with supX mutations are more sensitive than wild type to killing by ultraviolet (UV) irradiation. Studies with strains bearing the leuD21 mutation revealed that inactivation of the supX locus by a nonsense mutation or a deletion results in a complete lack of ability to produce induced Leu+ reversion mutations after UV irradiation. Suppression of the nonsense supX mutation or the presence of an Escherichia coli K-12 F'-borne supX+ allele restored the capacity for induced reversions and increased cell survival after UV irradiation. Introduction of plasmid pKM101 into supX mutant strains also restored their capacity for UV mutagenesis as well as increased survival. The possible nature of the supX gene product and mechanisms by which it may affect expression of the inducible SOS error-prone repair system are considered.