Synergy between ciprofloxacin and temperate phages overcomes therapeutic limitations caused by lysogen formation.

Bacteriophages have proven invaluable in combatting drug-resistant bacteria. Bias towards exclusive use of obligately lytic phages has restricted the range of phage therapy, however, since at least half of all Caudovirecetes are temperate, and such phages remain the only option available for many problematic pathogens - including the notorious members of the Burkholderia cepacia complex (Bcc). Temperate phage-antibiotic synergy (tPAS), a unique strategy that leverages lysogen-forming phages as adjuvants to traditional antibiotics, has been validated for phages infecting E. coli and P. aeruginosa and is a major step towards normalization of temperate phages in therapeutics. In this report, we extend tPAS to Burkholderia phages and show that combining these phages with subinhibitory doses of ciprofloxacin overcomes natural limitations in antibacterial activity caused by lysogen formation. We further demonstrate that the magnitude of this effect correlates with the lysogenization frequencies of utilized phages, meaning tPAS is tailored specifically to otherwise ineffective, highly lysogenic phages. Finally, we observed heterogeneity in lysogen depletion rates among synergizing phages, suggesting 'complete' lysogen depletion is not required for antibacterial synergy. Our results support the use of temperate phages as synergizing adjuvants against Bcc species, thereby substantially expanding the limited arsenal of tools available for combating these pathogens.