Accordingly, NER seems
to be involved in CIP-induced DNA damage, as demonstrated in deficient E. coli strains . Although both NER and HR may commit to the repair of DPCs, it has been proposed recently that DPCs with crosslinked proteins of sizes < 12–14 kDa are repaired by NER, whereas oversized DPCs are processed exclusively by RecBCD-dependent HR . If confirmed, the later mechanism should be preferred in the repair of DPCs involving topoisomerase subunits. The repair activity was not strictly related to viability. Although the nucleoid may appear normal after repair, particularly at the low dose (0.1 μg/ml), the bacteria may not be fully viable, possibly buy CP673451 because of the lack of total fidelity in restitution and the SOS response, resulting in an error-prone repair
. Some misrepaired lesions could lead to a non-viable cell. The DNA repair experiments emphasize the importance of achieving the necessary concentrations over a prolonged time for the successful clinical effect of quinolones. DNA repair PI3K inhibitor is not cited as a mechanism of decreased sensitivity to quinolones. Nevertheless, E. coli mutants with constitutive RecA expression or defective SOS induction may survive longer . It is possible that dysfunction of buy Selumetinib certain DNA repair processes may lead to a low sensitivity to CIP, and this could increase the effect of other coexisting mechanisms of resistance. This possibility needs to be explored. It is expected that resistance to fluoroquinolones would hinder the production of DSBs, which are slowly
or rarely produced. Because DSBs appear to correlate strongly with the MIC and viability, the DNA fragmentation assay should detect resistance accurately. The preliminary study of the DNA fragmentation analysis in the four E. coli strains with low sensitivity to CIP suggests that this is the case. The 1273 strain did not show a clear effect at the MIC dose and had a lower DNA fragmentation level than that observed in other strains at the same multiple of MIC dose. This phenomenon could be related to the accumulation of ID-8 multiple resistance mechanisms, such as multiple mutations in different topoisomerase subunits and in conjunction with altered outer membrane proteins and lipopolysaccharide, and increased activity of efflux systems . Since only J-53 and J-53qnrA1 strains are isogenic, the other strains could have other differences that could influence the results. Moreover, the growth inhibition may not be dependent on inhibition of the topoisomerases leading to DNA fragmentation and the possibility exists of unknown mechanisms of action. Conclusion The DNA fragmentation assay may be a simple and rapid test to evaluate the sensitivity and resistance to quinolones. We are currently performing more comprehensive assessment of different characterized CIP-resistant and CIP-sensitive E. coli strains and in clinical samples.