Host-specificity and therapeutic potential of novel Escherichia coli-targeting bacteriophages for bovine mastitis control

E. coli mastitis is a major production disease in dairy cattle and requires alternative treatments to antibiotics. In this context, phages are of growing interest, but their host specificity remains a challenge in therapy. This study aimed to characterize eight newly isolated phages for the control of E. coli mastitis, to assess their efficacy in milk and to investigate their specificity. Physicochemical characterization of the phages was performed, followed by in vitro stability and lytic activity assays in raw and heat-treated milks. Genome sequencing of phages and bacteria was performed to investigate phage attachment. Phage stability was maintained across physiological pH and temperature ranges, as well as in raw milk. Phage lytic activity demonstrated bacterial decreases below detection level, but regrowth occurred in raw milk after 5 h of incubation with 3/8 phages. A narrow host range was linked to the diversity of the bacterial collection and to the presence of two receptor-binding proteins among Tevenvirinae. Indeed, structural analysis of the proteins revealed a variable region in the long tail fiber and a conserved short tail fiber. In conclusion, phage specificity was mainly associated with the long tail fiber and milk components didn't hinder the efficacy of phages to control bovine mastitis, although resistance should be investigated.