Active bacteriophage biocontrol and therapy on sub-millimeter scales towards removal of unwanted bacteria from foods and microbiomes

Abstract

Bacteriophages can be used as antibacterial agents as a form of biological control, e.g., such as phage therapy. With active treatment, phages must “actively” produce new virions, in situ , to attain “inundative” densities, i.e., sufficient titers to eradicate bacteria over reasonable timeframes. Passive treatment, by contrast, can be accomplished using phages that are bactericidal but incapable of generating new phage virions in situ during their interaction with target bacteria. These ideas of active versus passive treatment come from theoretical considerations of phage therapy pharmacology, particularly as developed in terms of phage application to well-mixed cultures consisting of physically unassociated bacteria. Here I extend these concepts to bacteria which instead are physically associated. These are bacteria as found making up cellular arrangements or bacterial microcolonies—collectively, clonal bacterial “clumps”. I consider circumstances where active phage replication would be required to effect desired levels of bacterial clearance, but populations of bacteria nevertheless are insufficiently prevalent to support phage replication to bacteria-inundative densities across environments. Clumped bacteria, however, may still support active treatment at more local, i.e., sub-millimeter, within-clump spatial scales, and potential consequences of this are explored mathematically. Application is to the post-harvest biocontrol of foodborne pathogens, and potentially also to precise microbiome editing. Adequate infection performance by phages in terms of timely burst sizes, that is, other than just adsorption rates and bactericidal activity, thus could be important for treatment effectiveness even if bacterial densities overall are insufficient to support active treatment across environments. Poor phage replication during treatment of even low bacterial numbers, such as given food refrigeration during treatment, consequently could be problematic to biocontrol success. In practical terms, this means that the characterization of phages for such purposes should include their potential to generate new virions under realistic in situ conditions across a diversity of potential bacterial targets.

Evaluation of Phage Delivery Systems on Induced MotileAeromonasSepticemia inOreochromis niloticus

“…The phage titer introduced after infection was *10 10 and was expected to employ a passive therapy throughout the duration of the trial, since inundative doses of the phage cocktail were provided in all treatments. 31 High concentration of phages produced a good bacteriolytic response. This aspect can also be referred to as the therapeutic tier or the phage dosage needed to induce infection clearing.…”

Safety and Efficacy of a Phage, kpssk3, in an in vivo Model of Carbapenem-Resistant Hypermucoviscous Klebsiella pneumoniae Bacteremia

“…Considering this possibility, short-circulating phages can better prevent the potential side effects of PT. Notably, the peak blood kpssk3 concentration, approximately 10 6 PFU/ml, made achieving the inundation threshold (the minimum phage concentration that can reduce the number of sensitive bacteria), which was equal to 10 7 PFU/ml or higher according to different calculations, difficult (Abedon, 2017). Thus, the phage (kpssk3) must first undergo self-replication, and the titer must then exceed the inundation threshold, based on which the PT in a passive mode can occur and decrease the bacterial population (Cairns et al, 2009).…”

Isolation and Characterization of Listeria monocytogenes Phage vB_LmoH_P61, a Phage With Biocontrol Potential on Different Food Matrices

“…Finally, the presence of actively growing bacterial host cells vs. stationary phase cells seems vital for the application of phage as a biocontrol agent. Abedon (2017) distinguishes between an "active treatment" and a "passive treatment" for phage biocontrol. In an active treatment, phages should actively produce newly formed virions in situ to create sufficient titers to eradicate the bacterial pathogen over reasonable timeframes.…”

“…By contrast, passive treatment uses phages that are bactericidal but incapable of generating new phage virions during their interactions with the bacterial host cell. It could be argued that having actively growing host cells allows the phage to hijack its host's metabolic mechanisms allowing for successful completion of its lifecycle and release of newly formed phages into the surrounding environment (Abedon, 2017). L. monocytogenes strain 702, used in the second set of experiments, actively grew on the baby spinach leaves in comparison to strain 3053 used in the initial study, which did not grow during the course of the experiment.…”