Hydroquinine is an organic compound that is closely related to quinine-derivative drugs and contains anti-malarial and anti-arrhythmia activities. It has been also found in abundance in some natural extracts that possess antibacterial properties. However, there is little evidence demonstrating the antibacterial effect of hydroquinine. Therefore, we aimed to investigate the antibacterial properties of hydroquinine using broth microdilution methods. In addition, we evaluated the transcriptional responses of P. aeruginosa to hydroquinine-induced stress using RNA sequencing with transcriptomic analysis and validated the results using PCR-based methods. The MIC and MBC values of hydroquinine against all eight bacterial strains investigated ranged from 650 to 2500 and from 1250 to 5000 µg/mL, respectively. Transcriptomic analysis demonstrated that RND efflux pump transcripts were overexpressed (4.90–9.47 Log2 fold change). Using mRT-dPCR and RT-qPCR, we identified that mRNA levels of mexD and mexY genes were overexpressed in response to just half the MIC of hydroquinine in P. aeruginosa. In conclusion, we uncover the antimicrobial potential of hydroquinine as well as identify changes in gene expression that may contribute to bacterial resistance. Further work will be required to explore the efficacy and potential use of hydroquinine in the clinic.

Hydroquinine is an organic alkaloid compound that exhibits antimicrobial activity against several bacterial strains including strains of both drug-sensitive and multidrug-resistant P. aeruginosa. Despite this, the effects of hydroquinine on virulence factors in P. aeruginosa have not yet been characterized. We therefore aimed to uncover the mechanism of P. aeruginosa hydroquinine-sensitivity using high-throughput transcriptomic analysis. We further confirmed whether hydroquinine inhibits specific virulence factors using RT-qPCR and phenotypic analysis. At half the minimum inhibitory concentration (MIC) of hydroquinine (1.250 mg/mL), 254 genes were differentially expressed (97 downregulated and 157 upregulated). We found that flagellar-related genes were downregulated by between −2.93 and −2.18 Log2-fold change. These genes were consistent with the analysis of gene ontology and KEGG pathway. Further validation by RT-qPCR showed that hydroquinine significantly suppressed expression of the flagellar-related genes. By analyzing cellular phenotypes, P. aeruginosa treated with ½MIC of hydroquinine exhibited inhibition of motility (30–54% reduction) and pyocyanin production (~25–27% reduction) and impaired biofilm formation (~57–87% reduction). These findings suggest that hydroquinine possesses anti-virulence factors, through diminishing flagellar, pyocyanin and biofilm formation.

The main objective of the present study was to provide a comprehensive LCI

Tetrigona apicalis (Smith, 1857) is a common species of stingless bee found in lower northern Thailand. In previous studies, the propolis of stingless bees has been shown to have antibacterial properties, due to its chemically contained phenolic contents. The major component of propolis is resin. The purpose of this study, therefore, was to evaluate the antibacterial activities of crude resin extracts by disk diffusion and broth microdilution methods. We also determined the total phenolic contents using the Folin-Ciocalteau method and, to detect individual polyphenolic contents, we used the high performance liquid chromatographic method. Two samples of resin were collected from Thung Salaeng Luang National Park, Phitsanulok. The first sample was from fresh plants, which stingless bees used for nest construction. The second sample was taken from entrances of the bee’s nest. All samples were macerated in 30 % ethanol and incubated at room temperature for 14 days. The supernatants were filtered and ethanol residues then removed as ethanolic resin extracts (eREs). The antibacterial activity of the extracted resins against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 was examined. The disks containing 9 and 14 mg of eREs produced obvious inhibition zones against S. aureus, but did not show zones against E. coli and P. aeruginosa. The minimum inhibitory concentrations (MICs) of the eREs against the bacterial strains tested were variously between 6 and 48 mg/ml, whereas the minimum bactericidal concentrations (MBCs) were from 12 to 48 mg/ml. The amount of the total phenolic compounds in the eREs from the fresh resin was 9,908 mg of pyrogallol equivalent (PGE) per kg of eREs, and from the nest entrances, 14,740 mg per kg. We also found that hydroquinin had the highest concentration in both extracts. In conclusion, the crude resin extracts demonstrated antibacterial properties against the S. aureus, E. coli, and P. aeruginosa strains tested. They also contained phenolic compounds which were active antibacterial agents. We have identified new and novel knowledge which can be used as preliminary data, leading to further, more detailed, investigation of the mechanistic action of the resin against bacterial cells.

Tetrigona apicalis is a species of stingless bees found in Lower Northern Thailand. They normally construct their nest entrances as an external structure for protecting themselves from enemies. Their biological properties have not well characterized yet. The objectives of this study were to evaluate the antibacterial, antifungal and antiproliferative activities of their nest entrances. Samples were collected from four provinces and then extracted using 70% ethanol, finally called as ethanolic Nest Entrances Extracts (eNEEs). Broth microdilution method was applied to determine their antimicrobial effects. The cytotoxicity was examined to evaluate their anti-proliferative effects. The total phenolic and flavonoid concentrations were determined using colorimetric methods. Overall, the MICs were between 6.25 and >12.5 mg/mL against the bacteria tested whereas were between 1.56 and >12.5 mg/mL for the yeasts tested. The IC50 of HeLa cells was lower than that of LEP cells. TPC (19.3-24.1 mg PGE/g dried eNEEs) and TFC (2.4-4.8 mg QE/g dried eNEEs) contained in the eNEEs with the major substances of hydroquinin and quercetin. In conclusion, the Thai ethanolic nest entrance extracts possess the antibacterial, antifungal and anti-proliferative activities.