Effect of hydroquinine against pathogenic microorganisms and its mechanism

Abstract

Hydroquinine is an organic compound closely related to quinine-derivative drugs known to possess anti-malarial activity. Hydroquinine has also been found in abundance in some natural extracts and has been suggested to have antibacterial properties. However, there is limited evidence demonstrating the antibacterial properties of hydroquinine. Further, the exact mechanism of hydroquinine action against Pseudomonas aeruginosa has not yet been studied. Therefore, this study aimed to investigate the antibacterial properties of hydroquinine using broth microdilution method. In addition, this research has uncovered the mechanism of action of hydroquinine against P. aeruginosa by examining transcriptional changes using high‐throughput transcriptomic analysis. We further validate these findings using both genotypic analysis using PCR-based methods and phenotypic analysis. This study found that hydroquinine inhibited all eight bacterial reference strains tested. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) values of hydroquinine against all eight bacterial strains investigated ranged from 650–2,500 and 1,250–5,000 µg/mL, respectively. Transcriptomic analysis demonstrated that at ½ MIC of hydroquinine (1.250 mg/mL), 254 genes were differentially expressed (97 downregulated and 157 upregulated). Hydroquinine induced the upregulation of the RND-type efflux pump genes, a drug-resistant mechanism (4.90 to 9.47 Log2 fold change) and downregulation of virulence factor genes associated with flagella assembly, pathogenicity factors (-2.93 to -2.18 Log2‐fold change) in P. aeruginosa ATCC 27853. Furthermore, the expression of RND-type efflux pump genes were validated by multiplex quantitative reverse transcription PCR (mRT-qPCR) and an effluxR detection assay with multiplex reverse transcription digital PCR (mRT-dPCR) methods. It showed that ½ MIC of hydroquinine significantly induced the expression of the mexD and mexY genes in the P. aeruginosa strains. In addition, using the RT-qPCR method, the virulence factor gene expression associated with flagella assembly and quorum sensing showed significantly downregulated in P. aeruginosa ATCC strains under ½ MIC of hydroquinine treatment. Additionally, by analyzing cellular phenotypes of P. aeruginosa associated with virulence factors, treatment with ½ MIC of hydroquinine exhibited inhibition of motility, pyocyanin production and impaired biofilm formation. These results offer a detailed view of the global transcriptomic changes in P. aeruginosa in response to hydroquinine exposure, which is helpful in the understanding of the cellular strategies utilized during hydroquinine conditions and indicates a possible mechanism for P. aeruginosa inhibition after hydroquinine exposure.

-