In vitro and in vivo assessment of phage therapy against Staphylococcus aureus causing bovine mastitis

Objectives The aim of this study was to assess the efficacy of lytic bacteriophages onStaphylococcus aureus causing bovine mastitis, by in vitro and in vivo assays using Galleria mellonella and murine mastitis models. Methods Between May and December 2016, tenS. aureus (five methicillin-resistant and five methicillin-sensitive) isolates were isolated from milk samples of cattle with mastitis in Belgium and Norway. The isolates were assessed in vitro for their susceptibility to four lytic bacteriophages (Romulus, Remus, ISP and DSM105264) and subsequently in vivo in G. mellonella larvae and in murine mastitis model. Results Romulus, Remus and ISP showed a lytic activity against theS. aureus isolates in vitro. A larvae survival rate below 50% was observed at four days post inoculation in the groups infected with a methicillin-sensitive S. aureus isolate and treated with these three phages in vivo. An incomplete recovery of the mice mastitis was observed at 48 hours post inoculation in the groups infected and treated with the ISP phage in vivo. Conclusions The observations are much more pronounced statistically between the infected-PBS treated and infected-phage treated groups inG. mellonella and murine mastitis model demonstrating an effect of the phages against S. aureus associated with bovine mastitis