Effect of curcumin on the expression of ahyI/R quorum sensing genes and some associated phenotypes in pathogenic Aeromonas hydrophila fish isolates.

Quorum sensing (QS) in Aeromonas hydrophila is mainly based on the modulation of ahyI/R genes that regulates bacterial virulence determinant phenotypes. The use of QS inhibitors would be of particular interest in inhibiting bacterial pathogenicity and infections. In this study, we aimed to determine the effect of curcumin, a natural component of Curcuma longa, on the expression of QS regulating genes, ahyI and ahyR, as well as some QS regulated virulence characteristics in pathogenic fish isolated A. hydrophila strains. The minimum inhibitory concentration (MIC) of curcumin against bacteria was determined using the broth micro-dilution method and the expression of quorum sensing genes ahyI and ahyR among the bacteria treated with curcumin was determined using quantitative polymerase chain reaction (qPCR). Also, the effect of curcumin on some QS associated traits, including biofilm formation, swarming and swimming motility, proteolytic potential, and bacterial hemolytic activity was investigated. According to the results, curcumin, at a concentration of 32 µg/mL, significantly reduced the expression of both ahyI and ahyR genes among bacterial strains up to 64.2 and 91.0%, respectively. Moreover, curcumin efficiently inhibited bacterial biofilm formation, swimming, and swarming motility. Also, bacterial proteolytic activity was slightly reduced, while hemolytic activity was not significantly affected. This study demonstrated the use of curcumin to attenuate ahyI/R QS genes and several QS associated phenotypes in A. hydrophila. These findings indicate the therapeutic potential of curcumin as an anti-QS agent, to be used against A. hydrophila pathogenesis in aquaculture.

Proteochemometric modeling of the origin of thymidylate synthase inhibition.

Due to its crucial role in DNA synthesis, thymidylate synthase (TS) has been considered as a potential therapeutic target. Inhibition of the enzyme is a promising strategy for the treatment of some hyperproliferative diseases, including infections. As TS species-specific inhibitors would be able to distinguish between the host and the pathogens, developing highly selective inhibitors is of great clinical importance. TS is among the most highly conserved enzymes over evolutionary history, making the design of its species-selective inhibitor significantly challenging. The chemical interaction space, governed by a set of non-selective TS inhibitors, has been explored for human TS and its homologous proteins in both Toxoplasma gondii and Escherichia coli using proteochemometrics modeling (PCM). Validity, robustness, and prediction power of the PCM model have been assessed applying a diverse set of internal/external validation approaches. Our PCM model has provided major structural information, which is indeed of great help to design new TS species-specific inhibitors with the simultaneous inhibition ability toward both T. gondii and E. coli. To show applicability of the PCM model, new compounds have been designed based on structural information provided by the constructed model. Final results have been very promising with regard to selectivity ratios of the designed compounds for different TS isoforms, confirming the applicability of the PCM model.