Challenges and opportunities for cheat therapy in the control of bacterial infections

Exploiting social traits for clinical applications in bacteria and viruses

Despite generating a great deal of interest in the form of review papers, progress in exploiting social dynamics for treatment strategies against bacterial infection has made limited progress since it was suggested twenty years ago. In contrast, anti-viral strategies based on social interactions are entering clinical trial stage. We explore possible reasons for this difference and highlight areas where the two fields of research may learn from one another.

Molecular Engineering of AIE-Active Photosensitizers with High Biosafety for Effect Extracellular Antibacteria

Developing versatile photosensitizers to actualize selective antibacteria over normal cells presents an appealing yet significantly challenging task. In this study, a novel photosensitizer named DMMA-SCPI is rationally designed and facilely synthesized, which is demonstrated as a type-I photosensitizer featured by aggregation-induced emission tendency. DMMA-SCPI is capable of effectively eliminating both Galanz positive bacteria and Galanz negative bacteria in vitro and in vivo, and showed insignificant injury to normal cells and tissues, probably resulting from its pyridinium halide that has stronger adsorption property on negatively charged bacteria compared to normal cells, as well as its suitable antimicrobial activity. The antimicrobial activity of pyridinium salt type photosensitizer depends on the adsorptive activities on the surface of bacterial cells as well as the antimicrobial activity of the reactive oxygen species (ROS). Among three photosensitizers, DMMA-SCPI has better water solubility, which provides greater surface activity to adsorb bacteria. Moreover, DMMA-SCPI produces more superoxide anion radicals as ROS, which has proper antimicrobial activity with high biosafety for effect extracellular antibacteria.

Putting theory to the test: An integrated computational/experimental chemostat model of the tragedy of the commons

Cooperation via shared public goods is ubiquitous in nature, however, noncontributing social cheaters can exploit the public goods provided by cooperating individuals to gain a fitness advantage. Theory predicts that this dynamic can cause a Tragedy of the Commons, and in particular, a 'Collapsing' Tragedy defined as the extinction of the entire population if the public good is essential. However, there is little empirical evidence of the Collapsing Tragedy in evolutionary biology. Here, we experimentally demonstrate this outcome in a microbial model system, the public good-producing bacterium Pseudomonas aeruginosa grown in a continuous-culture chemostat. In a growth medium that requires extracellular protein digestion, we find that P. aeruginosa populations maintain a high density when entirely composed of cooperating, protease-producing cells but completely collapse when non-producing cheater cells are introduced. We formulate a mechanistic mathematical model that recapitulates experimental observations and suggests key parameters, such as the dilution rate and the cost of public good production, that define the stability of cooperative behavior. We combine model prediction with experimental validation to explain striking differences in the long-term cheater trajectories of replicate cocultures through mutational events that increase cheater fitness. Taken together, our integrated empirical and theoretical approach validates and parametrizes the Collapsing Tragedy in a microbial population, and provides a quantitative, mechanistic framework for generating testable predictions of social behavior.

Exploiting cooperative pathogen behaviour for enhanced antibiotic potency: A Trojan horse approach

Antimicrobial resistance poses an escalating global threat, rendering traditional drug development approaches increasingly ineffective. Thus, novel alternatives to antibiotic-based therapies are needed. Exploiting pathogen cooperation as a strategy for combating resistant infections has been proposed but lacks experimental validation. Empirical findings demonstrate the successful invasion of cooperating populations by non-cooperating cheats, effectively reducing virulence in vitro and in vivo. The idea of harnessing cooperative behaviours for therapeutic benefit involves exploitation of the invasive capabilities of cheats to drive medically beneficial traits into infecting populations of cells. In this study, we employed Pseudomonas aeruginosa quorum sensing cheats to drive antibiotic sensitivity into both in vitro and in vivo resistant populations. We demonstrated the successful invasion of cheats, followed by increased antibiotic effectiveness against cheat-invaded populations, thereby establishing an experimental proof of principle for the potential application of the Trojan strategy in fighting resistant infections.

Bacterial defences: mechanisms, evolution and antimicrobial resistance

Throughout their evolutionary history, bacteria have faced diverse threats from other microorganisms, including competing bacteria, bacteriophages and predators. In response to these threats, they have evolved sophisticated defence mechanisms that today also protect bacteria against antibiotics and other therapies. In this Review, we explore the protective strategies of bacteria, including the mechanisms, evolution and clinical implications of these ancient defences. We also review the countermeasures that attackers have evolved to overcome bacterial defences. We argue that understanding how bacteria defend themselves in nature is important for the development of new therapies and for minimizing resistance evolution.