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.