Synergistic disinfection by phage PLY101 and 1.3-dibromo-5.5-dimethylhydantoin (DBDMH) against resistant Proteus mirabilis

Proteus mirabilis, frequently carried in the gut, is best known for causing complicated infections. With the wide application of disinfectants and lytic phages are being revisited as alternative antimicrobials, whether phage-disinfectant synergy (PDS) can improve therapeutic efficacy remains scarce. To address this gap, we isolated a novel lytic phage, designated PLY101, from wastewater. Transmission-electron microscopy and genomic analyses identified PLY101 as a double-stranded-DNA virus of the genus Novosibovirus, whose 41.513-kb genome is collinear with classical Proteus phage PM_75 (NC_027363.1). PLY101 produced clear plaques (about 3 mm) on P. mirabilis LY101 and maintained high stability across pH 5–9 and temperatures up to 55 °C. We next screened the synergy efficiency of PLY101 in combination with eight important disinfectants representing the six major biocidal classes. Time-kill assays revealed that 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) exhibited synergy with PLY101. PLY101–DBDMH pair reduced the 12-h MIC of DBDMH 3-fold. Application of PLY101 with DBDMH also triggered extensive cell damage and enlarged cell cytoskeleton. Adsorption rate showed that PDS significantly promoted the adsorption of PLY101 at 10 min, indicating that changes of bacterial morphology accelerated the absorption to receptors. In all, this study establishes PLY101 as a model phage adjuvant that reinstates DBDMH potency against P. mirabilis while cutting disinfectants use, providing a choice for low-dose, phage-enhanced disinfectants against problematic pathogens.