Understanding the effects of aerodynamic and hydrodynamic shear forces on Pseudomonas aeruginosa biofilm growth

Abstract

Biofilms are communities of bacterial cells encased in a self-produced polymeric matrix and exhibit high tolerance towards environmental stress. Despite the plethora of research on biofilms, most biofilm models are produced using mono-interface culture in static flow conditions, and knowledge of the effects of interfaces and mechanical forces on biofilm development remains fragmentary. This study elucidated the effects of air-liquid (ALI) or liquid-liquid (LLI) interfaces and mechanical shear forces induced by airflow and hydrodynamic flow on biofilm growing using a custom-designed dual-channel microfluidic platform. Results from this study showed that comparing biofilms developed under continuous nutrient supply and shear stresses free condition to those developed with limited nutrient supply, ALI biofilms were four times thicker, 60% less permeable, and 100 times more resistant to antibiotics, while LLI biofilms were two times thicker, 20% less permeable, and 100 times more resistant to antibiotics. Subjecting the biofilms to mechanical shear stresses affected the biofilm structure across the biofilm thickness significantly, resulting in generally thinner and denser biofilm compared to their controlled biofilm cultured in the absence of shear stresses, and the ALI and LLI biofilm's morphology was vastly different. Biofilms developed under hydrodynamic shear stress also showed increased antibiotic resistance. These findings highlight the importance of investigating biofilm growth and its mechanisms in realistic environmental conditions and demonstrate a feasible approach to undertake this study using a novel platform.

Impacts of hydrodynamic conditions and microscale surface roughness on the critical shear stress to develop and thickness of early‐stage Pseudomonas putida biofilms

“…Here, we investigate two physical factors that control the development of early‐stage biofilms: hydrodynamic conditions and the roughness of the substrate surface. Hydrodynamic conditions and surface roughness have shown to play important roles in early‐stage biofilm growth (Cowle et al, 2020; Janjaroen et al, 2013; Krsmanovic et al, 2021; Zhang et al, 2011; Zhang et al, 2022; Zheng et al, 2021), yet, their impacts remain controversial. Under different hydrodynamic conditions, shear force can alter the morphology and wetting properties of biofilms (Recupido et al, 2020), change biofilm metabolic behaviors (Liu & Tay, 2002), and control biofilm structures (Stoodley et al, 1998).…”

Challenges and current advances in in vitro biofilm characterization

“…[ 18–20 ] Rich nutrients result in more active, robust biofilms more resistant to biocide treatment. [ 19,20 ] Biofilms formed under nutrient depletion contain stationary phase zones, and bacteria in this zone are less vulnerable to antibiotics. [ 21 ]…”

“…Take from [ 85 ] ; (C) a multifloor microfluidic device for bacterial culture on the air‐liquid interface. Taken from [ 20 ] ; (D) A topographic microfluidic device for anti‐biofilm fouling surface study. Adapted from [ 86 ] ; (E) A porous microfluidic device with a heterogeneous distribution of pores to mimic realistic surroundings of soil for biofilm studies.…”

“…Sufficient nutrients lead to denser biofilms with higher biomass, while limited nutrients can inhibit bacterial growth and biofilm formation. [18][19][20] Rich nutrients result in more active, robust biofilms more resistant to biocide treatment. [19,20] Biofilms formed under nutrient depletion contain stationary phase zones, and bacteria in this zone are less vulnerable to antibiotics.…”

Real‐time in‐situ electrochemical monitoring of Pseudomonas aeruginosa biofilms grown on air–liquid interface and its antibiotic susceptibility using a novel dual‐chamber microfluidic device

“…At least one study has demonstrated that biofilm susceptibility to treatment likely differs depending on whether they proliferate on ALI or LLI. Permeability of the biofilms, for example, has been demonstrated to be different between biofilms developed on ALI and LLI (Zhang, Silva, Young, et al, 2022). Hence, selecting a suitable interface to develop efficient biofilm‐killing approaches is crucial.…”