Analysis of antibacterial and antivirulence activities of certain compounds of natural origin on Proteus mirabilis strains

In this study, it was aimed to investigate the antibacterial and anti-pathogenic activities of some phytochemicals from terpenes and phenolics against Proteus mirabilis, a typical uropathogen. In this context, minimum inhibitor concentrations (MIC) of alpha-terpineol, bisabolol, decanol, farnesol, hederasaponin, carvacrol, quercetin, eugenol, eucalyptol, cinnamaldehyde, terpinen-4-ol and thymol were determined in clinical isolates of P. mirabilis isolated in Ege University Medical Faculty Medical Microbiology Department Bacteriology Laboratory and P. mirabilis HI4320 reference strain from Mobley Research Laboratories (Ann Arbor, USA). The combined effects of these compounds and antibiotics (co-amoxilav, co-trimoxazole, meropenem, nitrofurantoin, ceftazidime, ciprofloxacin) used in urinary tract infections (UTIs) were then examined using the checkerboard method. In addition, the effects of related compounds on the formation of swarming motility, urease expression and biofilm formation of the reference strain were investigated. Finally, the effects of compounds with inhibitory activity on the expression levels of certain genes (flaA, flhD, gnNA, HisG, mRpJ, ompF, rcB, rcSD, speB, umoC, ureD) that play a role in the regulation of virulence factors were examined by real-time reverse transcriptase polymerase chain reaction (RT-qPCR). Compounds showing the strongest antimicrobial activity are carvacrol (128-256 μg/ml), cinnamaldehyde (256-512 μg/ml) and thymol (128-512 μg/ml) according to the MIC values determined by microdilution method. However, no synergistic effect was observed at any concentration between antibiotics and compounds in combination studies. It has been shown that carvacrol, quercetin, cinnamaldehyde and thymol inhibit the swarming motility in a döşe dependent manner. Furthermore, cinnamaldehyde has been found to be a dose dependent inhibitör against urease expression. Carvacrol and thymol, which suppress the swarming motility, caused inhibition in the production of biofilms, although quercetin and cinnamaldehyde cause activation. When the effects of these compounds on the expression levels of selected genes were assessed, their effects were different depending on the form of the medium. In this thesis study, P. mirabilis, a model bacterium which is distinguished by prominent characteristics such as swarming motility, intensive urease synthesis, formation of crystallized biofilm, causing urinary tract and kidney stones were used, and compounds that commonly known such as thymol, carvacrol, cinnamaldehyde, quercetin were found effective against such properties. These compounds may also be effective against other uropathogens, together with this bacterium, which generally leads to polymicrobial infections. Timol and carvacrol are generally known to be toxic. However, quercetin and cinnamaldehyde have a very low toxicity. These compounds, which are used as food or in phytotherapy, are widely available in various plants. Given these advantages, it is foreseen that the relevant compounds may be utilized in the UTIs prophylaxis. Thus, by reducing the amount of antibiotics used, economic gains can be gained and the development of resistance can be reduced to a certain extent. Furthermore, the extent to which the catheter's life is prolenged when the compounds are used as coating agents should be investigated by in vivo studies, in addition to the in vitro studies performed within the scope of this thesis.