Browsing by Author "Ignatiou, Athanasios"

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    The absence or presence of a lytic coliphage affects the response of Escherichia coli to heat, chlorine, or UV exposure
    (Springer, 2018-03-15) Ameh, Ekwu Mark; Tyrrel, Sean; Harris, Jim A.; Ignatiou, Athanasios; Orlova, Elena V.; Nocker, Andreas
    Disinfection aims at maximal inactivation of target organisms and the sustainable suppression of their regrowth. Whereas many disinfection efforts achieve efficient inactivation when the effect is measured directly after treatment, there are questions about the sustainability of this effect. One aspect is that the treated bacteria might recover and regain the ability to grow. In an environmental context, another question is how amenable surviving bacteria are to predation by omnipresent bacteriophages. Provisional data suggested that bacteria when subjected to sublethal heat stress might develop a phage-resistant phenotype. The result made us wonder about the susceptibility to phage-mediated lysis for bacteria exposed to a gradient of chlorine and UV-LED disinfection strengths. Whereas bacteria exposed to low sublethal chlorine doses still underwent phage-mediated lysis, the critical chlorine Ct of 0.5 mg min/L eliminated this susceptibility and induced phage resistance in the cells that survived treatment. In the case of UV, even the smallest tested dose of 2.8 mJ/cm2 abolished phage lysis leading to direct regrowth. Results suggest that bacteria surviving disinfection might have higher environmental survival chances directly after treatment compared to non-treated cells. A reason could possibly lie in their compromised metabolism that is essential for phage replication.
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    Effect of temperature on bacteriophage-mediated lysis efficiency with a special emphasis on bacterial temperature history
    (University of Mohammed Premier, Oujda, Morocco, 2022-09-30) Ameh, Ekwu Mark; Nocker, Andreas; Tyrrell, Sean R.; Harris, Jim A.; Orlova, Elena V.; Ignatiou, Athanasios
    Despite the great potential of phages as biocontrol agents, there is much uncertainty about the environmental factors influencing lysis efficiency. In this study we investigated the effect of temperature using three distinct lytic E. coli phages that were isolated from a single environmental water sample. All three were identified as dsDNA phages belonging to the Myoviridae family. Whereas the optimal growth temperature of E. coli is well known to be 37 ˚C and exposure of phages (prior to mixing with bacteria) to temperatures between 4 and 37˚C did not affect their infectivity, plaque sizes and numbers greatly decreased with increasing incubation temperature (20˚C, 30˚C, 37˚C) of the phage-host mix. At 37˚C, no visible plaques were observed. Results suggest that temperature sensitivity of the phage-host interaction is distinct from the temperature susceptibility of the two players and corroborate previous reports that highest lysis rates are obtained at temperatures approximate with ambient conditions of the phage environment. Infectivity was however found not only to depend on the incubation temperature of the phage-host mix, but also on the bacterial temperature history. Moreover, exposure of bacteria to heat stress prior to phage challenge resulted in a phage-resistant phenotype raising the question whether bacterial pathogens shed from warm-blooded hosts might be less susceptible to phages adapted to environmental temperature conditions.
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    Lysis performance of bacteriophages with different plaque sizes and comparison of lysis kinetics after simultaneous and sequential phage addition
    (Mary Ann Liebert, 2020-09-16) Ameh, Ekwu Mark; Tyrrel, Sean; Harris, Jim A.; Pawlett, Mark; Orlova, Elena V.; Ignatiou, Athanasios; Nocker, Andreas
    Background: Although bacteriophages see a revival for specifically removing undesired bacteria, there is still much uncertainty about how to achieve the most rapid and long-lasting clearance. Materials and Methods: This study investigated the lysis kinetics of three distinct environmental coliphages, reproducibly forming different plaque sizes (big, medium, and small). Lysis performance by individual phages was compared with the one obtained after simultaneous or sequential addition of all three phages. Kinetics was monitored by density absorbance or by flow cytometry, with the latter having the advantage of providing higher sensitivity. Results: Plaque size happened to correlate with lysis kinetics in liquid suspensions, with phages producing big (phage B), medium (phage M), and small (phage S) plaques showing maximal bacterial clearance under the chosen conditions within ∼6, 12, and 18 h, respectively. Use of a phage cocktail (all three phages added simultaneously) resulted in slower initial lysis compared with the fastest lysing phage with the greatest plaque size alone, but it showed longer efficacy in suppression. When adding phages sequentially, overall lysis kinetics could be influenced by administering phages at different time points. The lowest bacterial concentration after 36 h was obtained when administering phages in the sequence S, M, and B although this combination initially took the longest to achieve bacterial clearance. Conclusions: Results support that timing and order of phage addition can modulate strength and duration of bacterial suppression and, thus, influence the overall success of phage treatment.