In Situ Investigation of Pseudomonas aeruginosa Biofilm Development: Interplay between Flow, Growth Medium, and Mechanical Properties of Substrate

Microfluidic Platform with Precisely Controlled Hydrodynamic Parameters and Integrated Features for Generation of Microvortices to Accurately Form and Monitor Biofilms in Flow

Microorganisms often live in habitats characterized by fluid flow, and their adhesion to surfaces in industrial systems or clinical settings may lead to pipe clogging, microbially influenced corrosion, material deterioration, food spoilage, infections, and human illness. Here, a novel microfluidic platform was developed to investigate biofilm formation under precisely controlled (i) cell concentration, (ii) temperature, and (iii) flow conditions. The developed platform central unit is a single-channel microfluidic flow cell designed to ensure ultrahomogeneous flow and condition in its central area, where features, e.g., with trapping properties, can be incorporated. In comparison to static and macroflow chamber assays for biofilm studies, microfluidic chips allow in situ monitoring of biofilm formation under various flow regimes and have better environment control and smaller sample requirements. Flow simulations and experiments with fluorescent particles were used to simulate bacteria flow in the platform cell for calculating flow velocity and direction at the microscale level. The combination of flow analysis and fluorescent strain injection in the cell showed that microtraps placed at the center of the channel were efficient in capturing bacteria at determined positions and to study how flow conditions, especially microvortices, can affect biofilm formation. The microfluidic platform exhibited improved performances in terms of homogeneity and robustness for in vitro biofilm formation. We anticipate the presented platform to be suitable for broad, versatile, and high-throughput biofilm studies at the microscale level.

Biofilm formation: mechanistic insights and therapeutic targets

Biofilms are complex multicellular communities formed by bacteria, and their extracellular polymeric substances are observed as surface-attached or non-surface-attached aggregates. Many types of bacterial species found in living hosts or environments can form biofilms. These include pathogenic bacteria such as Pseudomonas, which can act as persistent infectious hosts and are responsible for a wide range of chronic diseases as well as the emergence of antibiotic resistance, thereby making them difficult to eliminate. Pseudomonas aeruginosa has emerged as a model organism for studying biofilm formation. In addition, other Pseudomonas utilize biofilm formation in plant colonization and environmental persistence. Biofilms are effective in aiding bacterial colonization, enhancing bacterial resistance to antimicrobial substances and host immune responses, and facilitating cell‒cell signalling exchanges between community bacteria. The lack of antibiotics targeting biofilms in the drug discovery process indicates the need to design new biofilm inhibitors as antimicrobial drugs using various strategies and targeting different stages of biofilm formation. Growing strategies that have been developed to combat biofilm formation include targeting bacterial enzymes, as well as those involved in the quorum sensing and adhesion pathways. In this review, with Pseudomonas as the primary subject of study, we review and discuss the mechanisms of bacterial biofilm formation and current therapeutic approaches, emphasizing the clinical issues associated with biofilm infections and focusing on current and emerging antibiotic biofilm strategies.

Design, Synthesis, and Biological Evaluation of Phenyloxadiazole Sulfoxide Derivatives as Potent Pseudomonas aeruginosa Biofilm Inhibitors

With the development of antimicrobial agents, researchers have developed new strategies through key regulatory systems to block the expression of virulence genes without affecting bacterial growth. This strategy can minimize the selective pressure that leads to the emergence of resistance. Quorum sensing (QS) is an intercellular communication system that plays a key role in the regulation of bacterial virulence and biofilm formation. Studies have revealed that the QS system controls 4-6% of the total number of P. aeruginosa genes, and quorum sensing inhibitors (QSIs) could be a promising target for developing new prevention and treatment strategies against P. aeruginosa infection. In this study, four series of phenyloxadiazole and phenyltetrazole sulfoxide derivatives were synthesized and evaluated for their inhibitory effects on P. aeruginosa PAO1 biofilm formation. Our results showed that 5b had biofilm inhibitory activity and reduced the production of QS-regulated virulence factors in P. aeruginosa. In addition, silico molecular docking studies have shown that 5b binds to the P. aeruginosa QS receptor protein LasR through hydrogen bond interaction. Preliminary structure-activity relationship and docking studies show that 5b has broad application prospects as an anti-biofilm compound, and further research will be carried out in the future to solve the problem of microbial resistance.