(150d) Unveiling the Critical Roles of Cellular Metabolism Suppression in Antibiotic Tolerance

Metabolic inhibitors are believed to exhibit antagonistic effects in the presence of antibiotics, as they are known to promote cell survival by inducing bacterial dormancy. However, the specific synergistic or antagonistic effects of metabolic inhibitors depend on their mechanisms of action, treatment timings, and their concentrations within treatment cultures, which require further investigation. Here, we systematically examined the synergistic and antagonistic effects of various metabolic inhibitors, such as chloramphenicol (a translation inhibitor), rifampicin (a transcription inhibitor), arsenate (an ATP production inhibitor), and thioridazine (a PMF inhibitor), in combination with ofloxacin (a quinolone antibiotic). These investigations were conducted under pre-, co-, and post-treatment conditions, encompassing a wide range of concentrations. When we applied four distinct synergy models (Highest Single Agent, Loewe, Bliss, and Zero Interaction Potency), which provide numerical scores indicating the degree of synergy (positive score), additivity (zero score), or antagonism (negative score) in drug combinations¹, we consistently observed that chloramphenicol, rifampicin, and arsenate received low or negative synergy scores, indicating a significant antagonistic relationship with ofloxacin. In contrast, thioridazine consistently received higher synergy scores, especially in pre- and co-treatment scenarios; however, its synergy decreased during post-treatment conditions. When we used multivariable linear regression analyses for all drugs and conditions tested here, a correlation between the synergy of thioridazine and its ability to suppress cellular energy metabolism became evident. While our study highlights the dual nature of metabolic inhibitors, it also underscores that compounds like PMF inhibitors can display significant potency and synergistic effects with antibiotics, suggesting their potential utility as effective anti-microbial adjuvants.