Niepa μBiointerface Lab

The emergence of antibiotic-resistant bacteria has presented an increasing challenge to infection control. In general, bacterial populations commonly harbor phenotypic variants, known as persister cells, which are metabolically inactive and extremely tolerant to antibiotics. The persister cells are well known to survive conventional antibacterial treatments and regenerate the bacterial populations with a similar percentage of persister cells when the antibiotic treatment is stopped. The electrochemical control of persister cells (ECCP) presents a great potential for the treatment of chronic infections. We demonstrated that bacterial persister cells could be effectively eliminated by low-level direct currents (DCs) alone, and in synergy with antibiotics. The discovery showed that DC treatments could affect the surface charge and membrane integrity of P. aeruginosa and increase the intracellular interaction of metal cations and antibiotics with the nucleic acid.

Electrochemical treatments mediated via carbon electrodes can provoke the permeabilization of the cells to extracellular materials and lead to complete eradication of the persisters. These findings, corroborated by DNA microarray analysis, reveal that DC treatments have profound effects on the physiology of persister cells, altering the regulation of genes involved in antibiotic resistance, pyocin-related functions, and SOS response. The safety and efficacy of ECCP is further tested in co-culture models with human epithelial cells and P. aeruginosa PAO1 and in rabbit model of sinus infections. Overall, the study aims to improve the understanding of the electrophysiology of bacterial persister cells, and provides new insight for designing novel systems to effectively control infections associated with biofilms and persister cells.

Each year, massive amounts of oil are accidentally or deliberately spilled into seawaters, polluting the ecosystem. Quick remediation responses, including in-situ burning or dispersant spraying, have been insufficient to palliate the long-lasting harm caused by the spills. One avenue that might address this need is to exploit more effectively the inherent abilities of microorganisms to break down oil molecules. Because of the large interfacial tensions between oil and water, it is expected that manipulating the properties of the bacterial films could optimize the performance of bacteria in the oil field, direct microbial dynamics toward hydrocarbon degradation, and thereby ameliorate ecosystem recovery. The premise underlying this research plan consists of elucidating the mechanisms of film formation at oil-water interface and ultimately improving the designs of sustainable bioremediation solutions. This study aims to answer three major questions: (1) how does the physical interaction between bacterial films and oil-water interfaces enhance or impede hydrocarbon bioremediation; (2) how can the community behavior and interactions among marine bacteria be utilized to benefit bioremediation; and (3) how can hydrocarbon degradation be assisted and sustained by means of eco-friendly technology? This research incorporates physical and biological approaches to describe the mechanisms of film formation at the oil-water interfaces and explain its impact on oil remediation. Moreover, sustainable models of biodegradation are assessed to promote hydrocarbon bioavailability by means of functionalized nanoparticles.

Cover art: ACS Appl. Bio Mater. 2022, 5, 5, 1868–1878

Bacterial infection of medical and environmental surfaces is a common phenomenon encountered in various settings. On solid surfaces, for instance, a cell has to overcome physical forces or surface charges to colonize and develop into mature films. The secretion of the exopolysaccharide (EPS) matrix becomes essential to protect the embedded cells from "adverse" environments and to control the exchange of nutrients and genetic materials. Within the biofilm, bacteria become about 1000 times more tolerant to antibiotics than their planktonic counterparts. Moreover, the presence of a sub-population of slow-growing or dormant cells (known as persister cells), which are highly resistant to antibiotics, render biofilms difficult to eradicate. Under more favorable conditions, the persisters can "wake up" and repopulate the biofilms then disperse, colonizing new areas and causing chronic infection.

Unfortunately, the physiological responses of cells to environmental stress, which contributes to bacteria adopting distinctive community behaviors, are poorly understood. The goal of this research is to understand how microbial dynamics in confined environments are affected by physico-chemical stresses, such as antibiotics, electrochemical current, and osmotic pressure. Thus, bacterial cells confined in well-defined nanocultures (2-5 nL) are subjected to external stress to examine phenotypic variation associated with cell-cell communication and persister and microcolony formation. The findings of this study may contribute to the design of novel detection and control techniques for bacterial colonization and for the testing of novel antimicrobials. Such applications are significant for the food and pharmaceutical industries through the encapsulation of microorganisms in microemulsions.

Cover art: ACS Appl. Polym. Mater. 2022, 4, 5, 2999–3012