Physicochemical characterization of ten newly isolated phages against the foodborne pathogen Shigella flexneri

Abstract

Ten bacteriophages with lytic activity against Shigella flexneri were tested for their resistance to physicochemical conditions found in food matrices. Phage viability and activity were evaluated at different temperatures, pH values, and NaCl concentrations.In addition, challenge tests with each individual phage against ATCC 12022 were conducted to evaluate their use as biocontrol agents. Although phages showed high resistance up to 60°C, Shi30, Shi33, and Shi93 showed higher thermal resistance (70°C).The ten phages endured pH treatments, being more resistant to alkaline conditions. The NaCl concentrations evaluated showed no significant influence on phage counts. Furthermore, challenge tests against ATCC 12022 resulted in significant CFU ml −1 reductions. The results showed that the phages evaluated were resistant to a wide range of temperatures and pH and to all the concentrations of NaCl tested. Therefore, the phages evaluated in this study could potentially be used with biocontrol purposes in various food matrices prior further characterization.Novelty impact statement: Ten newly isolated phages against the foodborne pathogen Shigella flexneri remained viable after different physicochemical treatments. Furthermore, their activity was maintained after thermal and chemical treatments. Also, the ten phages were effective against pathogenic Shigella flexneri strains in challenge tests.

Influence of Physicochemical Factors on Adsorption of Ten Shigella flexneri Phages

“…Our previous results indicated that phage viability was not significantly affected from pH 5 to pH 11, yet, at pH 3, a significant reduction in viability was observed. In addition, the activity of the 10 phages tested in this work was the same at 5 < pH < 9 and was slightly affected at 3 < pH < 5 and 9 < pH < 11 [14]. As previously observed by others [8,20,28], our phages were highly stable in a wide range of pH values (Figure 4).…”

“…Prior to adsorption assays, viability of phages at refrigeration (4 • C), room (25 • C) and abusive (50 • C) temperatures was evaluated. All the phages tested showed a high resistance from 4 to 50 • C [14]. In agreement, two phages (vB_SflS-ISF001 and vB-SdyS-ISF003) active against S. flexneri [18] and S. dysenteriae [24], respectively, proved to have a high thermal stability in the range of -20 to 60 • C. Phages adsorbed efficiently at low (Shi3, Shi22, Shi30, Shi33, Shi34 and Shi88), at moderate (AShi, Shi34, Shi40, Shi93 and Shi113) and at high (AShi, Shi 22, Shi30 and Shi33) temperatures.…”

“…In this study, 10 bacteriophages, namely AShi, Shi3, Shi22, Shi30, Shi33, Shi34, Shi40, Shi88, Shi93 and Shi113, previously isolated from 114 stool samples [14], were used to evaluate their growth curve and adsorption characteristics.…”

“…A better understanding of phage-host interactions in different abiotic conditions can lead to more effective biocontrol treatments. Although studies on the isolation or characterization of Shigella phages have been conducted [13,14], those focusing on adsorption of S. flexneri phages have hardly been documented.…”

“…In our previous study, 10 phages lytic against S. flexneri strains were isolated and characterized by their host range and challenge assays, including stability tests under various stress conditions [14]. Thus, the aim of the present work was to characterize the phagehost interaction through parameters of the phage cycle and adsorption constants (k), and to evaluate the influence of physicochemical conditions relevant to food processing on phage adsorption to improve the efficiency of application on the food matrix.…”