Improving Phage-Biofilm In Vitro Experimentation

Bacteriophages or phages, the viruses of bacteria, are abundant components of most ecosystems, including those where bacteria predominantly occupy biofilm niches. Understanding the phage impact on bacterial biofilms therefore can be crucial toward understanding both phage and bacterial ecology. Here, we take a critical look at the study of bacteriophage interactions with bacterial biofilms as carried out in vitro, since these studies serve as bases of our ecological and therapeutic understanding of phage impacts on biofilms. We suggest that phage-biofilm in vitro experiments often may be improved in terms of both design and interpretation. Specific issues discussed include (a) not distinguishing control of new biofilm growth from removal of existing biofilm, (b) inadequate descriptions of phage titers, (c) artificially small overlying fluid volumes, (d) limited explorations of treatment dosing and duration, (e) only end-point rather than kinetic analyses, (f) importance of distinguishing phage enzymatic from phage bacteriolytic anti-biofilm activities, (g) limitations of biofilm biomass determinations, (h) free-phage interference with viable-count determinations, and (i) importance of experimental conditions. Toward bettering understanding of the ecology of bacteriophage-biofilm interactions, and of phage-mediated biofilm disruption, we discuss here these various issues as well as provide tips toward improving experiments and their reporting.

Epidemiological dynamics of bacteriocin competition and antibiotic resistance

Bacteriocins, toxic peptides involved in bacterial fratricide, are extremely diverse. Understanding the mechanisms that maintain this diversity is an important aim in bacterial ecology. Previous work on bacteriocin diversity has focused on dynamics, particularly ‘rock-paper-scissors’ dynamics, at the within-host scale. Yet, in species such as Streptococcus pneumoniae, with relatively short periods of colonisation and limited within-host diversity, processes at the epidemiological scale also shape eco-evolutionary dynamics. Here, we investigate bacteriocin dynamics in epidemiological models. We find that in these models, bacteriocin diversity arises more readily than in within-host models, and with more possible combinations of coexisting bacteriocin profiles. We also investigate a potential link between bacteriocin diversity and diversity at antibiotic resistance loci. Previous work has proposed that bacterial duration of carriage modulates the fitness of antibiotic resistance. We predict bacteriocins modulate duration of carriage, making them a plausible candidate for involvement in resistance dynamics.