Effect of combination of doxycycline with natural products against planktonic cells, biofilm, and virulence factor of Pseudomonas aeruginosa

Abstract

Background: Pseudomonas aeruginosa is an important environmental, opportunistic, and nosocomial pathogen with a significant threat to public health. Combination therapy has many advantages due to the simultaneous action of two drugs on two separate cellular targets. In the present study, the effect of combination of doxycycline and natural products against planktonic cells, biofilm, and virulence factors of P. aeruginosa was evaluated.

Methods: To perform this work, minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of doxycycline and natural products were determined by broth microdilution method. The microtiter plate assay method was used to determine the minimal biofilm inhibitory concentration (MBIC) and the minimum biofilm eradication concentration (MBEC). The effect of doxycycline and natural products against pyocyanin, swarming motility, and swimming motility was evaluated. The checkerboard method was used to evaluate the effect of combination of doxycycline with natural products against planktonic and biofilm cells.

Results: The MIC of doxycycline ranged between 2 µg/mL and 128 µg/mL with an average of 35.89 µg/mL. Sinapic acid showed the best inhibitory activity against planktonic cells with an average MIC of 27.79 µg/mL. At the sub-inhibitory concentrations, the pyocyanin production, swarming motility decrease, and swimming motility decrease. Out of the six combinations tested, combination formed by doxycycline and sinapic acid exhibited synergistic activity for the prevention of biofilm formation with a 6-fold reduction in MBIC of doxycycline.

Conclusion: This study revealed that doxycycline and sinapic acid combination could be considered as promising candidate for the development of therapy against P. aeruginosa infections.