Abstract
Lytic phages are potential therapeutic options, based on their ability to lyse bacteria in vitro. Although many infection-types for which phage therapy is being considered involve biofilms, in vitro anti-biofilm activity of phage is poorly defined, in part due to a lack of standardized methods for assessment. Here, phages SaMD07phi1 and SaRBI05030phi5 were evaluated against Staphylococcus aureus SaMD07 and SaRBI05030, respectively, in biofilms formed in 96-well plates and on glass beads, and planktonically, in TSB and PBS, with endpoints including by CFUs and Biolog Omnilog hold times. The bead biofilm assay in TSB using the Omnilog (BBTO) was employed to test eight staphylococcal phages against S. aureus, Staphylococcus epidermidis, and Staphylococcus lugdunensis from periprosthetic joint infection. Biofilms on beads in TSB showed better eradication than in microtiter wells, with no significant changes with PBS in either format. CFU counts and Omnilog units correlated linearly through 8 h of testing. In the bead assay, CFU counts showed that phage SaMD07phi1 eliminated growth at 4 h, while SaRBI05030phi5 achieved a ~ 3-log reduction at 8 h; with Omnilog hold times of 37 and 28 h, respectively. Diverse activity and good reproducibility of the BBTO was observed among 8 phages, with SaMD07phi1 showing the highest activity. In conclusion the BBTO is a promising potential method for biofilm susceptibility testing.