Bacteriophage therapy: A Renewed Approach to fight multidrug resistant bacteria
Sadika Dkhili1,2, Salma Ghariani2, Houssem Ben Yahia1,2 , Aouatef Ben Ammar3 , Sami Zekri3 , Karim Ben Slama1,2

1 Laboratoire des Microorganismes et Biomolécules actives, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 Tunis, Tunisie
2 Institut Supérieur des Sciences Biologiques Appliquées de Tunis, Université de Tunis El Manar, 1006 Tunis, Tunisie
3 USCR Microscopie Électronique à Transmission, Faculté de Médecine de Tunis, Université Tunis El Manar, 1006 Tunis, Tunisie

Context and problematics: Enterobacteriaceae are a large family of Gram-negative Bacilli, being Escherichia coli one of the most representative species of this family. Some E. coli strains have developed mechanisms of pathogenicity; they are considered to be the most important opportunistic pathogens which mean they can cause human and animal diseases. β-lactams are considered the most powerful antimicrobial agents both in human and veterinary medicine. However, resistance to this class of antibiotics has been reported to increase over time especially in Gram-negative bacteria such as E. coli. Antibiotic resistance is considered today a worrying and evolving phenomenon and even a major global public health problem. The importance of the current situation urgently requires another bactericidal alternative of special and collective interest in order to tackle multidrug resistant bacteria.

Objectives: Alternative or complementary treatment is requested. The aim of this study was to explore bacteriophages as potential antimicrobial agents against ESBL-producing E. coli.

Methodology: Twenty-four virulent phages were isolated from wastewater samples in Tunisia, purified by the double-layer agar method. The lytic activity of the purified phages was tested using 49 bacterial strains. Phage morphology was visualized by transmission electron microscopy (TEM), and life cycle parameters, physicochemical properties and bacterial challenge assays of phages were carried out.

Results and discussion: From a collection of 24 virulent phages infecting different genera and species of bacteria multiresistant to antibiotics, we selected 3 lytic phages specific to ESBL-producing E.coli whose results are: Morphological analyze revealed that the three extended spectrum beta-lactamase (ESBL) producing Escherichia coli phages belong to the Caudovirales order, Siphoviridae and Myoviridae family. The isolated phages have broad host ranges that can target two bacterial genus and two bacterial species. These phages were resisted to acid and basic pH. These phages maintained their infectious powers during a storage period of 6 months under different temperature conditions with tolerance to a different temperature range. The use of the phage cocktail SD1, SD2 and SD3 proved to be promising in the control of Escherichia coli infections.

Conclusion: The rapid adsorption, the short latency period, the enormous quantity of phages released from the infected host, the low frequency of Bacteriophage Insensitive Mutants (BIMs) and the broad host ranges with a wide tolerance to temperature; pH and chloroform clearly showed that these three phages were excellent lytic phages with very suitable potential therapeutic applications.