Soojin Jang. BMB Reports 2023;56:326-34. https://doi.org/10.5483/BMBRep.2023-0070

Antibiotic resistance is rapidly spreading among bacteria such as Staphylococcus aureus, an opportunistic bacterial pathogen that causes a variety of diseases in humans. For the last two decades, bacterial multidrug efflux pumps have drawn attention due to their potential association with clinical multidrug resistance. Numerous researchers have demonstrated efflux-mediated resistance in vitro and in vivo and found novel multidrug transporters using advanced genomic information about bacteria. This article aims to provide a concise summary of multidrug efflux pumps and their important clinical implications, focusing on recent findings concerning S. aureus efflux pumps.

Thiamine pyrophosphate (TPP) is an essential cofactor for various pivotal cellular processes in all living organisms, including bacteria. Thiamine biosynthesis occurs in bacteria but not in humans, so the enzymes in this pathway are attractive targets for antibiotic development. Among these enzymes, thiamine monophosphate kinase (ThiL) catalyzes the final step of this pathway, phosphorylating thiamine monophosphate (TMP) to produce TPP. Here, we extensively investigated ThiL in Pseudomonas aeruginosa, a major pathogen responsible for hospital-acquired infections. We demonstrate that thiL deletion abolishes not only thiamine biosynthesis, but also thiamine salvage capability, and results in growth defects of the ΔthiL strain even in the presence of thiamine derivatives, except for TPP. Most importantly, the pathogenesis of the ΔthiL strain was markedly attenuated compared with wild-type cells, with lower inflammatory cytokine induction and 10³–10⁴-fold decreased bacterial load in an in vivo infection model where the intracellular TPP level was in the submicromolar range. To validate P. aeruginosa ThiL (PaThiL) as a drug target, we further characterized its biochemical properties, determining a V_max of 4.0 ± 0.2 nmol·min^-1 and K_M values of 111 ± 8 and 8.0 ± 3.5 μM for ATP and TMP, respectively. An in vitro small-molecule screening identified PaThiL inhibitors, including WAY213613, a noncompetitive inhibitor with a Ki value of 13.4 ± 2.3 μM and potential antibacterial activity against P. aeruginosa. These comprehensive biological and biochemical results indicate that PaThiL represents a potential drug target for the development of an augmented repertoire of antibiotics against P. aeruginosa.

Small molecule can be utilized to restore the effectiveness of existing major classes of antibiotics against antibiotic‐resistant bacteria. In this study, it is demonstrated that celastrol, a natural compound, can modify the bacterial cell wall and subsequently render bacteria more suceptible to β‐lactam antibiotics. It is shown that celastrol leads to incomplete cell wall crosslinking by modulating levels of c‐di‐AMP, a secondary messenger, in methicillin‐resistant Staphylococcus aureus (MRSA). This mechanism enables celastrol to act as a potentiator, effectively rendering MRSA susceptible to a range of penicillins and cephalosporins. Restoration of in vivo susceptibility of MRSA to methicillin is also demonstrated using a sepsis animal model by co‐administering methicillin along with celastrol at a much lower amount than that of methicillin. The results suggest a novel approach for developing potentiators for major classes of antibiotics by exploring molecules that re‐program metabolic pathways to reverse β‐lactam‐resistant strains to susceptible strains.