Enhancement of pyocyanin production by subinhibitory concentration of royal jelly in Pseudomonas aeruginosa

Abstract

Background: Pseudomonas aeruginosa, a multidrug resistant Gram-negative bacterium, produces pyocyanin, a virulence factor associated with antibiotic tolerance. High concentrations of royal jelly have an antibacterial effect, which may have the potential to overcome antibacterial resistance. However, in some cases, antibiotic tolerance can occur due to prolonged stress of low-dose antibacterial agents. This study aimed to investigate the effect of subinhibitory concentrations of royal jelly on bacterial growth and pyocyanin production of P. aeruginosa. Methods: Pseudomonas aeruginosa ATCC® 10145™ and clinical isolates were cultured in BHI media for 18 hours followed by optical density measurements at 600 nm wavelength to determine minimum inhibitory concentration (MIC). After 36 hours of incubation, pyocyanin production was observed by measuring the absorbance at 690 nm. Pyocyanin concentrations were calculated using extinction coefficient 4310 M-1cm-1. Results: Results of the MIC tests of both strains were 25%. The highest production of pyocyanin was observed in the subinhibitory concentration group 6.25%, which gradually decreased along with the decrease of royal jelly concentration. Results of one-way ANOVA tests differed significantly in pyocyanin production of the two strains between the royal jelly groups. Tukey HSD test showed concentrations of 12.5%, 6.25%, and 3.125% significantly increased pyocyanin production of ATCC® 10145™, and the concentrations of 12.5% and 6.25% significantly increased production of the clinical isolates. Conclusions: This study concluded royal jelly concentrations of 25% or above could inhibit bacterial growth; however, only the concentrations of 12.5% and 6.25% could increase pyocyanin production in P. aeruginosa, both in ATCC® 10145™ and clinical isolates. In conclusion, it is advisable to determine the appropriate concentration of royal jelly to obtain beneficial virulence inhibiting activity.