Synergistic effects of bacteriophages combined with antibiotics against multidrug-resistant uropathogenic Klebsiella pneumoniae

The global threat of multidrug-resistant pathogens necessitates novel strategies for their control. Research on the synergistic effects of bacteriophages and antibiotics against these pathogens is gaining attraction worldwide. This investigation employed two previously isolated and characterized bacteriophages, KPA and KP-PHA-Meh, to assess their combined effect with sub-inhibitory concentrations of cefepime, gentamicin, and meropenem against a multidrug-resistant, biofilm-producing uropathogenic Klebsiella pneumoniae strain isolated from the urine of a 23-year-old female patient. Complete growth inhibition of planktonic cells was achieved when cefepime at 8 µg or meropenem at 1 µg was combined with either phage at MOI 0.1, where reductions of up to 4-log CFU were observed at lower sub-inhibitory concentrations of these antibiotics. KPA alone inhibited biofilm formation by up to 26.7% at an MOI of 0.1. The addition of cefepime or meropenem further enhanced the antibiofilm activity of both phages compared with phage treatment alone. In contrast, gentamicin at 4, 2, and 1 µg/mL reduced the antibacterial and antibiofilm activity of both phages, an antagonistic effect that was reversed only at the lowest concentration tested (0.5 µg/mL), at which synergy was restored. On glass slides, KPA completely eradicated preformed biofilm, while KP-PHA-Meh reduced its quantity. Throughout the study, KPA demonstrated superior performance in bacterial eradication and biofilm inhibition, both independently and in combination with antibiotics, compared to KP-PHA-Meh. This superior performance of KPA may be linked to depolymerase-associated genomic features, including endosialidase and lysozyme motifs in its tail fiber protein.