Comparison of single and multi-host enrichment approach for harnessing lytic phages against antimicrobial-resistant E. coli: Repurposing the enrichment step

Escherichia coli has been enlisted as a pathogen of antimicrobial resistance (AMR) importance posing a threat to human health. In the wake of the widespread AMR, lytic bacteriophages remain a promising alternative to antibiotics for controlling the multidrug-resistant (MDR) pathogens. However, the major hindrance for phage therapy is the lack of a rapid procedure to harness broad host range phages. Hitherto in vogue, lytic phage isolation methods are based on conventional single host enrichment (M1). Limitation to the available methods includes a higher number of steps, additional instrumentation, cost and time involved in the screening of samples and more recovery of narrow host range phages.To improve the conventional method of isolation, a multiple host enrichment approach (modified method; M2) is developed and validated with a classical approach using 24 MDR extended-spectrum beta-lactamase producing (ESBL) E. coli and universal coliphage host E. coli NCIM 2089. A total of 58 phages were isolated using both the methods (27 phages from M1 and 31 phages from M2) and were categorized, based on the DNA restriction digestion pattern, to 25 groups with a maximum host range of 17 in host range analysis. Even though there is no significant difference (P > 0.01) in recovering number of phages between M1 and M2 methods, excepting in one occasion where MFB13 host yielded 3 more morphologically distinct phages in M2 (p <= 0.05), the M2 approach was better in terms of reduction in time (4.72%) and cost (23.5%) and same instrumentation requirement. This emphasizes that the proposed method has the potential to yield broad host range lytic phages against localized strain repository of AMR E. coli which can be leading to its application in food, food contact surfaces as well as phage therapy.