Lipoxin A4 promotes antibiotic and monocyte bacterial killing in established Pseudomonas aeruginosa biofilm formed under hydrodynamic conditions

Pseudomonas aeruginosa is a gram-negative, opportunistic bacteria commonly found in wounds and in lungs of immunocompromised patients. These bacteria commonly form biofilms which encapsulate the bacteria, making it difficult for antibiotics or immune cells to reach the bacterial cells. We previously reported that Lipoxin A4 (LxA4 ), a Specialized Pro-resolving Mediator, has direct effects on P. aeruginosa where it reduced biofilm formation and promoted ciprofloxacin antibiotic efficacy in a static biofilm-forming system. In the current studies, we examined the actions of LxA4 on established biofilms formed in a biofilm reactor under dynamic conditions with constant flow and shear stress. These conditions allow for biofilm growth with nutrient replenishment and for examination of bacteria within the biofilm structure. We show that LxA4 helped ciprofloxacin reduction of live/dead ratio of bacteria within the biofilm. THP-1 monocytes interacted with the biofilm to increase the number of viable bacteria within the biofilm as well as TNF-α production in the biofilm milieu, suggesting that monocyte interaction with bacterial biofilm exacerbates the inflammatory state. Pre-treatment of the THP-1 monocytes with LxA4 abolished the increase in biofilm bacteria and reduced TNF-α production. The effect of decreased biofilm bacteria was associated with increased LxA4 -induced monocyte adherence to biofilm but not increased bacteria killing suggesting that the mechanism for the reduced biofilm bacteria was due to LxA4 -mediated increase in adherence to biofilm. These results suggest that LxA4 can help antibiotic efficacy and promote monocyte activity against established P. aeruginosa biofilm formed under hydrodynamic conditions.