Effects of sequential administration of phage cocktail, ciprofloxacin, and caspofungin on Staphylococcus aureus and Candida albicans dual-species biofilms

Polymicrobial biofilms, including inter-kingdom ones, represent another threat in the post-antibiotic era. Therefore, many alternative solutions are being investigated, including phage-antibiotic synergy (PAS), which may be more effective due to the differing mechanisms of action of drugs and phages. In this study, we evaluated how different sequences of administering a bacteriophage cocktail, ciprofloxacin, and caspofungin affect the eradication of S. aureus and C. albicans in vitro (planktonic culture and in biofilms). In liquid culture, the phage → caspofungin → ciprofloxacin treatment completely eradicated both organisms. In biofilms, the most effective regimens were either the simultaneous application of all three agents or phages + ciprofloxacin followed by caspofungin. Therefore, the sequence of administration of drugs and phages is a key factor in achieving effective therapy and revealing the most synergistic combinations.