Abstract
Antibacterial compounds that affect bacterial viability have traditionally been identified, confirmed, and characterized in standard laboratory media. The historical success of identifying new antibiotics via this route has justifiably established a traditional means of screening for new antimicrobials. The emergence of multi-drug-resistant (MDR) bacterial pathogens has expedited the need for new antibiotics, though many in the industry have questioned the source(s) of these new compounds. As many pharmaceutical companies' chemical libraries have been exhaustively screened via the traditional route, we have concluded that all compounds with any antibacterial potential have been identified. While new compound libraries and platforms are being pursued, it also seems prudent to screen the libraries we currently have in hand using alternative screening approaches. One strategy involves screening under conditions that better reflect the environment pathogens experience during an infection, and identifying in vivo essential targets and pathways that are dispensable for growth in standard laboratory media in vitro. Here we describe a novel screening strategy for identifying compounds that inhibit the glyoxylate shunt in Pseudomonas aeruginosa, a pathway that is required for bacterial survival in the pulmonary environment. We demonstrate that these compounds, which were not previously identified using traditional screening approaches, have broad-spectrum antibacterial activity when they are tested under in vivo-relevant conditions. We also show that these compounds have potent activity on both enzymes that comprise the glyoxylate shunt, a feature that was supported by computational homology modeling. By dual-targeting both enzymes in this pathway, we would expect to see a reduced propensity for resistance development to these compounds. Taken together, these data suggest that understanding the in vivo environment that bacterial pathogens must tolerate, and adjusting the antibacterial screening paradigm to reflect those conditions, could identify novel antibiotics for the treatment of serious MDR pathogens.
Highlights
The threat of multi-drug-resistance in Gram-negative pathogens has grown from being a rare, isolated incident to an inevitability occurring worldwide
While the most significant consideration and progress in identifying such an inhibitor has been conducted with M. tuberculosis [35], the orthologous pathway in P. aeruginosa has been implicated numerous times in various virulence and in vivo survival models [36,37]
Given that the glyoxylate shunt has been shown to be essential for survival in environments where lipids are the primary source of carbon, it was not surprising that no differences in virulence were seen when these strains were tested in a septicemia model of infection
Summary
The threat of multi-drug-resistance in Gram-negative pathogens has grown from being a rare, isolated incident to an inevitability occurring worldwide. Pathogens have become so recalcitrant to conventional antimicrobial therapy that combinations of antibiotics, or antibiotics with known toxicity liabilities are required in order to have a chance at defeating them. In many cases these approaches prove unsuccessful, leading to extended hospitalizations, and can result in costly device replacements, life-altering amputations, or even death. Of particular concern to the infectious diseases community has been the identification of new sources of antibacterial compounds for testing against these serious MDR pathogens [4]. While much of this concern is warranted due to the underwhelming number of leads recently identified from both target-based and traditional whole cell screening efforts [5], the development and implementation of novel, non-traditional whole cell screens – using the same compound libraries already in existence – have yet to be described
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