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Front. Public Health | doi: 10.3389/fpubh.2019.00355

Characterisation of lytic bacteriophages infecting multi-drug resistant shiga-toxigenic atypical Escherichia coli O177 strains isolated from cattle faeces

  • 1North-West University, South Africa
  • 2University of Mpumalanga, South Africa

The increasing incidence of antibiotic resistance and emergence of virulent bacterial pathogens, coupled with a lack of new effective antibiotics, has reignited interest in the use of lytic bacteriophage therapy. The aim of this study was to characterise lytic E. coli O177-specific bacteriophages isolated from cattle faeces to determine their potential application as bio-control agents. A total of 31 lytic E. coli O177-specific bacteriophages were isolated. A large proportion (71%) of these phage isolates produced large plaques while 29% produced small plaques on 0.3% soft agar. Based on different plaque morphology and clarity and size of plaques, eight phages were selected for further analyses. Spot test and efficiency of plating (EOP) analyses were performed to determine the host range for selected phages. Phage morphotype and growth were analysed using transmission electron microscopy and the one-step growth curve method. Phages were also assessed for thermal and pH stability. The spot test revealed that all selected phages were capable of infecting different environmental E. coli strains. However, none of the phages infected ATCC and environmental Salmonella strains. Furthermore, EOP analysis (range: 0.1 to 1.0) showed that phages were capable of infecting a wide range of E. coli isolates. Selected phage isolates had similar morphotype (an icosahedral head and a contractile tail) and were classified under the order Caudovirales, Myoviridae family. The icosahedral heads ranged from 81.2 nm to 110.77 nm while the contractile tails ranged from 115.55 nm to 132.57 nm in size. The phages were found to be still active after 60 minutes of incubation at 37 °C and 40 °C. Incremental levels of pH induced a quadratic response on stability of all phages. The pH optima for all eight phages ranged between 7.6 and 8.0 while at pH 3.0 all phages were inactive. Phage latent period ranged between 15 to 25 minutes while burst size ranged from 91 to 522 virion particles (PFU) per infected cell. These results demonstrate that lytic E. coli O177-specific bacteriophages isolated from cattle faeces are highly stable and have the capacity to infect different E. coli strains, traits that make them potential biocontrol agents.

Keywords: atypical enterophagenic E. coli O177, Bacteriophages, biocontrol, Biological properties, multi-drug resistant, Shiga-toxigenic E. coli

Received: 10 Jul 2019; Accepted: 07 Nov 2019.

Copyright: © 2019 Montso, Mlambo and Ateba. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Collins Njie Ateba, North-West University, Potchefstroom, 2520, North West, South Africa, collins.ateba@nwu.ac.za