In each case, complementation was observed (Fig. 3). Thus, at least for this selection of genes Tipifarnib ic50 it is likely that the gene products contributed to reducing the lethal effects of nalidixic acid. While these data do not assure that

complementation will occur in the other cases, they give us confidence to move forward with the study of the bacterial response to lethal stress. We note in some cases paradoxical survival occurred at high concentrations of nalidixic acid. This phenomenon, which is unexplained, is commonly observed with quinolones [39]. Figure 3 Complementation of hyperlethal phenotype by cloned genes. Plasmids 17-AAG mouse containing wild-type genes were transformed into the corresponding Tn5-containing mutants. The strains harboring the plasmids were then tested for nalidixic acid-mediated lethality by treating mid-log phase cells with various concentrations of nalidixic acid for 2 hr at 37°C. Percent of control indicates percent survival of treated cells relative to untreated cells sampled at the time of drug addition. For ycjW, yrbB, and ybcM, the expression was induced by adding 1 mM of IPTG 2 hr before nalidixic acid treatment. Similar results were obtained in a replicate experiment. Conclusions The present work described a novel screening process for identifying genes involved in protecting E. coli from quinolone-mediated death due to events occurring after formation of NU7441 price quinolone-gyrase-DNA

complexes. Using this screen we identified 14 poorly characterized genes. Scattered evidence suggests that many of these Etoposide order genes are linked to protective stress responses, which is supported by our finding that mutations in these putative protective genes resulted in decreased survival following treatment with several stressors. The diverse set of genes described may serve as potential targets

for future screening of small-molecule antimicrobial potentiators. Acknowledgements This work was supported by National Natural Science Foundation of China (Grant No. 30860012) and Natural Science Foundation of Yunnan Province of China (Grant No. 2005C0007R) to T.L, NIH grants AI35257 and AI 073491 to K.D, and NIH grant AI068014 to XZ. References 1. Levy SB: Antibiotic resistance-the problem intensifies. Adv Drug Deliv Rev 2005,57(10):1446–1450.PubMedCrossRef 2. Levy SB, Marshall B: Antibacterial resistance worldwide: causes, challenges and responses. Nat Med 2004,10(12 Suppl):S122–129.PubMedCrossRef 3. Buynak JD: Understanding the longevity of the beta-lactam antibiotics and of antibiotic/beta-lactamase inhibitor combinations. Biochem Pharmacol 2006,71(7):930–940.PubMedCrossRef 4. Nelson ML, Levy SB: Reversal of tetracycline resistance mediated by different bacterial tetracycline resistance determinants by an inhibitor of the Tet(B) antiport protein. Antimicrobial agents and chemotherapy 1999,43(7):1719–1724.PubMed 5.