Bacteriophage Fitness Indicated by Modeled Adsorption Efficacy

Introduction:  Biofilm-forming shiga-toxin-producing Escherichia coli(STEC) are an emerging problem in the food industry, rendering traditional antimicrobials ineffective. Bacteriophages, natural bacterial predators, could be effective biocontrol agents against STEC. Their mode of action involves adsorption through host bacterial cell-membrane matrix. Therefore, understanding the nature of phage adsorption, using reliable predictive models, is crucial for their applicability in food system.

Purpose:  To predict bacteriophage fitness through adsorption efficiency

Methods:  Isolated bacteriophages, specific for non-O157 STEC (O26, O45, O103, O111, O121, O145), were used. For adsorption experiment, overnight cultures of non-O157 STEC were centrifuged and re-suspended in buffer along with respective phage, at 0.1 multiplicity-of-infection. The mixture was incubated at 37°C and sampled for 80 mins with 20 mins interval, followed by serial-dilution and filtration. Filtered samples were assayed to determine residual phage population using the double-agar-layer technique. Adsorption rate (k) and efficiency (€) was determined through adsorption-kinetics model using SigmaPlot13^TM(Systat Software, US). Adsorption-equilibrium time was also determined; hypothetically assuming that adsorption process reached an equilibrium. Diffusion constant (D) was determined using standard equation.

Results:  The r² values (0.93-0.99) suggested that chosen adsorption-kinetics model best described the adsorption data for all phages. The k-values varied from 1.46 x10^-5 to 7.41 x10^-5 PFU/ml/s indicating that phages had varied adsorption rates with susceptible host. All the phages had high adsorption rates, with the highest € observed at 74%. Adsorption-equilibrium time was determined to be 40 mins for all phages. D-values for all phages varied from 1.18 x10^-1 to 2.32 x10^-2cc/s. These results indicate that bacteriophages with high adsorption-rate, coupled with high diffusion constant, can be regarded as “fit” to disrupt STEC cell membranes.

Significance:  Bacteriophage fitness and equilibrium time could help select potential phages for the development of application protocols in food-systems.