Antimicrobial Effect of Roselle (Hibiscus sabdariffa L.) Water Fraction against Pseudomonas aeruginosa using Drosophila Infection Model

Pseudomonas aeruginosa is one of the most common pathogenic bacteria that cause nosocomial infection. Unfortunately, the irrational use of antibiotics has created a surge in P. aeruginosa resistance nowadays. To overcome this situation, new antibacterial compounds are urgently needed. One of the potential sources to obtain such antibacterial compounds is roselle calyx. This research was carried out using two experimental approaches, survival assay and gene expression analysis, to examine the in vivo antibacterial effect of water fraction of roselle calyx (WFR) against Pseudomonas aeruginosa in Drosophila model of infection. Survival assay was used to demonstrate the impact of treatment on the lifespan of the infected host. The measurement of immune-related Dpt mRNA levels by reverse-transcriptase quantitative PCR (RT-qPCR) was used to assess whether immunostimulation is involved in the antibacterial protection of WFR against P. aeruginosa. The result demonstrated that WFR at concentrations of 0.8% and 2% were able to enhance P. aeruginosa-infected flies' survival. Furthermore, gene expression analysis showed the insignificant difference between WFR-treated flies and healthy control flies at all tested concentrations, implying the non-involvement of Imd-Dpt-mediated pathway immunity in the antipseudomonal protection of WFR. Taken together, our data suggested the in vivo antibacterial activity of WFR against P. aeruginosa in the fruit fly model of infection.