Validation of the AlamarBlue® Assay as a Fast Screening Method to Determine the Antimicrobial Activity of Botanical Extracts

Abstract

Plant compounds are a potential source of new antimicrobial molecules against a variety of infections. Plant extracts suppose complex phytochemical libraries that may be used for the first stages of the screening process for antimicrobials. However, their large variability and complexity require fast and inexpensive methods that allow a rapid and adequate screening for antimicrobial activity against a variety of bacteria and fungi. In this study, a multi-well plate assay using the AlamarBlue® fluorescent dye was applied to screen for antimicrobial activity of several botanical extracts and the data were correlated with microbial colony forming units (CFU). This correlation was performed for three pathogenic model microorganisms: Escherichia coli (Gram negative bacteria), Staphylococcus aureus (Gram positive bacteria) and for the yeast-like fungi Candida albicans. A total of ten plant extracts from different Mediterranean plants, including several Cistus and Hibiscus species, were successfully tested. HPLC-DAD-ESI-MS/MS analysis was utilized for the characterization of the extracts in order to establish structure-activity correlations. The results show that extracts enriched in ellagitannins and flavonols are promising antibacterial agents against both Gram positive and Gram negative bacteria. In contrast, phenolic acids, anthocyanidins and flavonols may be related to the observed antifungal activity.

Modeling photocatalytic degradation of diazinon from aqueous solutions and effluent toxicity risk assessment using Escherichia coli LMG 15862

“…By measuring the turbidity in the suspension, the density of the bacterial cells was obtained in the range of 2–3 × 10 8  cells/mL. To determine the mortality rate of E. coli bacteria, 100 µL of bacterial suspension was injected on a plate containing the Mueller–Hinton medium and diazinon (Nasiry et al 2007; Gregoraszczuk et al 2015; Balouiri et al 2016; Tyc et al 2016; Toolabi et al 2017). After 24 h of incubation, the growth inhibition percentage was determined by Eq.…”

“…But in the presence of living bacteria, alamar blue is converted to resorufin and the color of the solution changes from blue to pink (Nasiry et al 2007; Rampersad 2012; Gregoraszczuk et al 2015; Balouiri et al 2016; Tyc et al 2016; Zare et al 2016; Teh et al 2017; Toolabi et al 2017). To achieve the best and most effective method of removal and risk assessment of diazinon in aqueous solution, more studies need to be done in this regard.…”

Preclinical Evaluation of the Antimicrobial-Immunomodulatory Dual Action of Xenohormetic Molecules against Haemophilus influenzae Respiratory Infection

“…Ampicillin (Amp, Sigma-Aldrich) and azithromycin dihydrate (Azm, Zytromax) 10 mg/mL stock solutions were prepared in distilled H 2 O (dH 2 O) and filtered. Four plant extracts rich in polyphenols were used: Cistus salviifolius extract (45% w/w polyphenols) was obtained as previously described [35]; Punica granatum extract (20% w/w punicalagins) was provided by Nutracitrus S.L. (Elche, Spain); Hibiscus sabdariffa (6% w/w polyphenols) and Lippia citriodora (30% w/w phenylpropanoids) extracts were provided by Nutrafur S.L.…”

“…Cistus salviifolius and Punica granatum extracts, containing ellagitannins and flavonoids, were selected for this study due to their previously seen antibacterial effects [29,43]. Hibiscus sabdariffa and Lippia citriodora extracts were selected based on their antifungal activity and their efficacy against some bacteria [35]. We first tested the susceptibility of the clinical strain NTHi375 to these four plant extracts rich in polyphenols and observed a significant dose-dependent reduction of bacterial viability after incubation with the C. salviifolius extract ( Figure 1A).…”

“…This observation was also made for the reference strain RdKW20, which also showed lower viability at the highest P. granatum concentrations tested ( Figure S1A). These observations prompted us to analyze the effect of three polyphenols, quercetin, myricetin, and punicalagin, the most representative aglycones of the large variety of glycosylated polyphenols present in the C. salviifolius extract [35]. The three molecules reduced NTHi bacterial viability in a dose-dependent manner, quercetin being the one with the lowest MIC observed ( Figure 1B and Figure S1B).…”