Purpose: Here we further characterized the Salmonella phages in our growing library in terms of growth kinetics and survivability under various conditions.
Methods: Single-step growth kinetics were measured in Salmonella serovars Typhimurium, Kentucky and Enteritidis. Survivability was measured under varying pH, temperature, incubation with digestive enzymes, microwave and UV irradiation.
Results: There was a large amount of variability in bacteriophage growth rates (ranging from 0.0001 phage/cell/minute to 75 phage/cell/minute), adsorption rates (ranging from 0.54 phage/cell/minute to 0.99 phage/cell/minute), burst sizes (ranging from 0 to 4,567 particles) and latent periods (ranging from 21 min to 99 min). Overall, our phages had highest killing efficiencies in serovar Typhimurium. All phages showed lower killing efficiencies in serovar Kentucky. At pH 4.0, phage viability decreased by 0.5 log viable particles after 180 minutes. Similarly, phage viability decreased by 1.7 log viable particles at pH 10.0 after 180 minutes. Phages were significantly affected by acidic environments as there was a > 99.0% reduction in the number of viable particles at pH 2.0 after 5 min. Phages were unaffected by low concentrations of trypsin or chymotrypsin, but were quickly inactivated by incubation in 0.05% hypochlorite (chlorine is commonly used in drinking water in US poultry production). All phages were quickly inactivated by both microwave and UV irradiation (320 nm and 365 nm).
Significance: Thus, different phages possessed widely different killing efficiencies in vitro, but displayed more uniform survivability characteristics under different manufacturing conditions. Taken together, these data may help us predict other areas where phage-based therapies may be effective and appropriate as part of a biocontrol strategy.