Caracterització fenotípica dels bacteriòfags lítics d’Escherichia coli

Abstract

Environmental bacteriophages are the most abundant and diverse biological entities in the

biosphere and play a fundamental ecological role in controlling bacterial populations and

biogeochemical cycles.

This study addresses the investigation of certain virulent bacteriophages, characterized by

their lytic cycle, which provides them with properties suitable for an environmental biocontrol

strategy: phage therapy. This innovative therapy uses bacteriophages to eliminate pathogens

in water, soil, or food, making them a viable alternative to the global threat of antimicrobial

resistance.

These therapeutic bacteriophages must exhibit high lytic efficiency, a broad host range, or

considerable resistance to adverse environmental conditions. In this study, a phenotypic

characterization was carried out on four lytic Escherichia coli bacteriophages isolated from

wastewater treatment plant effluents: I1.1, E1.3, EUR3.2, and E1.1.A.

Initially, the bacteriophages were selected through a host range assay using various E. coli

strains. For each virus, lysis curves were evaluated at different MOI values (Multiplicity of

Infection) with E. coli WG5. All strains showed reductions greater than 94% at an MOI of 0.1,

except for EUR3.2, which required an MOI of 1 to achieve an equivalent effect. Additionally,

replication curves were described, showing very long latency periods for all phages—ranging

from 30 to 60 minutes—and low burst sizes, with results of 4 to 30 viral particles per infected

cell. Finally, the physicochemical stability of the bacteriophages of interest was assessed

under the effects of salinity, UV radiation, and temperature, calculating their stability using the

D50 parameter (the dose required to reduce the population by 50%). The D50 values for the

different tested variables ranged from 7 to >10‰ for salinity, from 7.51 to 116 mJ for UV

radiation, and from 24.4 to 54.6°C for temperature. The results demonstrate effective

replication in the lysis curves, although the replication assays do not correlate and should be

further investigated. On the other hand, the stability values fall within acceptable ranges for

application in various environments.

This analysis of the studied bacteriophages provides valuable information on their potential

use as an innovative tool, contributing to ecosystem balance and the protection of public

health

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