Chronic infections often contain complex mixtures of pathogenic and commensal microorganisms ranging from aerobic and anaerobic bacteria to fungi and viruses. The microbial communities present in infected tissues are not passively co-existing but rather actively interacting with each other via a spectrum of competitive and/or cooperative mechanisms. Competition versus cooperation in these microbial interactions can be driven by both the composition of the microbial community as well as the presence of host defense strategies. These interactions are typically mediated via the production of secreted molecules. In this review, we will explore the possibility that microorganisms competing for nutrients at the host–pathogen interface can evolve seemingly cooperative mechanisms by controlling the production of subsets of secreted virulence factors. We will also address interspecies versus intraspecies utilization of community resources and discuss the impact that this phenomenon might have on co-evolution at the host–pathogen interface.

The human microbiota is an array of microorganisms known to interact with the host and other microbes. These interactions can be competitive, as microbes must adapt to host- and microorganism-related stressors, thus producing toxic molecules, or cooperative, whereby microbes survive by maintaining homeostasis with the host and host-associated microbial communities. As a result, these microbial interactions shape host health and can potentially result in disease. In this review, we discuss these varying interactions across microbial species, their positive and negative effects, the therapeutic potential of these interactions, and their implications on our knowledge of human well-being.

Cystic fibrosis (CF) is a genetic disease frequently associated with chronic lung infections caused by a consortium of pathogens. It is common for auxotrophy (the inability to biosynthesize certain essential metabolites) to develop in clinical isolates of the dominant CF pathogen Pseudomonas aeruginosa, indicating that the CF lung environment is replete in various nutrients. Many of these nutrients are likely to come from the host tissues, but some may come from the surrounding polymicrobial community within the lungs of CF patients as well. To assess the feasibility of nutrient exchange within the polymicrobial community of the CF lung, we selected P. aeruginosa and Staphylococcus aureus, two of the most prevalent species found in the CF lung environment. By comparing the polymicrobial culture of wild-type strains relative to their purine auxotrophic counterparts, we were able to observe metabolic complementation occurring in both P. aeruginosa and S. aureus when grown with a purine-producing cross-species pair. While our data indicate that some of this complementation is likely derived from extracellular DNA freed by lysis of S. aureus by the highly competitive P. aeruginosa, the partial complementation of S. aureus purine deficiency by P. aeruginosa demonstrates that bidirectional nutrient exchange between these classic competitors is possible.

Early detection of cancer remains a major challenge in oncology. Circulating tumour markers (CTMs), including circulating tumour cells, circulating tumour DNA, exosomes, microRNAs, and tumour-associated proteins, offer a minimally invasive strategy for monitoring tumour dynamics through liquid biopsy. However, their clinical translation is limited by low abundance, heterogeneity, and instability in body fluids. Recent advances in nanotechnology have enabled the development of highly sensitive and specific nano-biosensors that address many of these barriers. This review highlights the current progress in CTM detection using electrochemical, optical, plasmonic, and microfluidic-integrated platforms. Advanced nanomaterials such as graphene, carbon nanotubes, noble metal nanoparticles, quantum dots, and nanozymes are discussed for their roles in signal amplification, surface functionalization, and biomarker selectivity. Special focus is placed on lab-on-a-chip and wearable biosensors for multi-marker, point-of-care testing. To amplify the signals associated with nanobiosensors, various technologies, such as surface functionalization, aptamer and antibody functionalization, and nanozymes, have been integrated with the nanobiosensors.