Investigating antibacterial mechanisms of hydroquinine against Pseudomonas aeruginosa and its application as preventive contact lens solution

Abstract

Pseudomonas aeruginosa is one of the most common causes of contact-lens-related microbial keratitis (CLMK). Previous studies reported that disinfecting solutions were ineffective in preventing biofilm formation. Solutions containing novel natural agents may be an excellent option for reducing the risk of CLMK. Hydroquinine has antimicrobial potential with demonstrated activity against several bacteria, including drug-sensitive (DS) and multidrug-resistant (MDR) P. aeruginosa reference strains. Despite this, there is limited evidence confirming the antibacterial activity of hydroquinine against clinical isolates and the underlying mechanism of action. Here, this study aimed to investigate the antibacterial effect of hydroquinine in clinical P. aeruginosa strains using phenotypic antimicrobial susceptibility testing and synergistic testing. This study examined the potential inhibitory mechanisms against MDR P. aeruginosa isolates using molecular docking analysis in combination with RT-qPCR. Furthermore, this study investigated the antibacterial, anti-adhesion, and anti-biofilm properties of hydroquinine formulated multipurpose solutions (MPSs) compared to MPSs alone.

These thesis finding uncovered that hydroquinine inhibits and kills clinical P. aeruginosa at 2.50 mg/mL (MIC) and 5.00 mg/mL (MBC), respectively. Hydroquinine also showed partial synergistic effects with ceftazidime against clinical MDR P. aeruginosa strains. Using molecular docking, this study identified potential interactions between arginine deiminase (ADI) pathway-related proteins and hydroquinine. Furthermore, using RT-qPCR, hydroquinine directly affected the mRNA expression of the arc operon. This study demonstrated that the ADI-related genes, including the arginine/ornithine antiporter (arcD) and the three enzymes; arginine deiminase (arcA), ornithine transcarbamylase (arcB), and carbamate kinase (arcC) were significantly downregulated at half MIC of hydroquinine. Moreover, hydroquinine directly affected the expression levels of adhesion-related genes, namely cgrC, cheY, cheZ, fimU, and pilV. Using ISO 14729 stand-alone testing, hydroquinine met the criteria (>99.9% killing at disinfection time) against both P. aeruginosa reference and clinical strains. Using the crystal violet retention assay and FE-SEM, MPSs combined with hydroquinine were effective in inhibiting P. aeruginosa adhesion and destroying preexisting biofilms.

This study is the first report that the ADI-related proteins are potential molecular targets for the inhibitory effect of hydroquinine against clinically isolated MDR P. aeruginosa strains. Moreover, this is also the first report that hydroquinine-containing formulations have potential use as a contact lens disinfecting solution for adhesion inhibition and biofilm destruction. These findings may aid in the development of novel disinfectants aimed at combating P. aeruginosa, thereby potentially reducing the incidence of CLMK.

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