Sabbah, A. | bioRxiv Science

bioRxiv2025

Identifying Modulators of the Post-Antibiotic Effect

The post-antibiotic effect (PAE) is the delay in bacterial regrowth following antibiotic removal. It has important implications for dosing regimens since drugs that have extended activity following their elimination can be dosed less frequently, widening the therapeutic window. While the PAE has been associated with target vulnerability and the rate of target turnover, little is known about the genetic components that modulate the PAE. Here, we developed a high-throughput assay to screen the Escherichia coli Keio collection of [~]4000 deletion strains, identifying genes that enhance the PAE for CHIR-090, an inhibitor of UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC). This screen revealed approximately 400 gene knockouts that enhanced the PAE of CHIR-090. The list of PAE enhancers was enriched for genes involved in transmembrane transport and outer membrane synthesis. Notably, deletion of the rfaE gene, which is involved in lipopolysaccharide (LPS) biosynthesis, increased the PAE of the LpxC inhibitors CHIR-090 and LPC-058 by 2 h and 3 h, respectively. Consistent with this phenotype, co-treatment of wild-type E. coli with an RfaE inhibitor increased the PAE of CHIR-090 or LPC-058 by 1 h. To probe the mechanism of this interaction, we measured the rate of LpxC turnover and found that knocking out rfaE reduced its half-life by 2-fold, suggesting that disrupting RfaE increases the stability of LpxC, increasing target vulnerability and enhancing the PAE of LpxC inhibitors. SIGNIFICANCEAntibiotics are generally dosed at very high levels leading to unwanted side effects and non-compliance, which in turn results in the emergence of drug-resistant bacterial infections. The goal of this work was to develop strategies that will enable antibiotics to be dosed at lower levels, thereby improving safety and compliance. In the present work, we have screened 4,000 strains of Escherichia coli to identify compounds that result in an increase in the post-antibiotic effect (PAE), which is the delay in bacterial regrowth following antibiotic exposure and removal. Drugs that cause a PAE are dosed less frequently, and the method we describe will provide a new approach to developing safer drugs.

microbiology↗

bioRxiv2023

SPATEs promote the survival of Shigella to the plasma complement system upon hemorrhage and bacteremia

Shigella spp. are the causative agents of shigellosis, which remains a leading cause of death in children under the age of five. Shigellosis is characterized by fever and results in hemorrhagic diarrhea; in more severe cases, Shigella bacteremia has been reported. These clinical features strongly suggest that Shigella survive exposure to plasma, although this has not yet been studied at the molecular level. In this report, we confirmed in a guinea pig model of shigellosis that local hemorrhages were induced by S. flexneri 5a and S. sonnei, and we demonstrated that Shigella reached mucosal CD31+/CD34+ blood vessels during the late stages of infection and further disseminated in the bloodstream. These results confirmed the exposure of Shigella to plasma components within the hemorrhagic colonic mucosa and in the bloodstream. We demonstrated that all the tested Shigella strains survived plasma exposure in vitro, and we showed that Serine Protease Autotransporters of Enterobacteriaceae (SPATEs) are essential for Shigella dissemination within the colonic mucosa. We have confirmed that SPATEs are expressed and secreted in poorly oxygenated environments encountered by Shigella from hypoxic foci of infection to the bloodstream. We further demonstrated that SPATEs promoted Shigella survival in plasma, by cleaving complement component 3 (C3), thereby impairing complement system activation. We have shown here that the ability of Shigella to survive plasma exposure is a key factor in its virulence, both within primary foci and systemically. Significance StatementIn this study we aimed to better understand the significance of the ability of Shigella to survive plasma exposure, as we observed that non-pathogenic E. coli rapidly lysed upon exposure. Indeed, we reported that Shigella was already exposed to plasma components within the colonic mucosa, as we reported in a guinea pig model of shigellosis that hemorrhages were induced, that were associated with local diffusion of plasma components in the infected colonic mucosa. Shigella was obviously exposed to plasma during bacteremia. The ability of Shigella to survive in plasma has not been previously reported. Here we have shown, first, that Shigella was able to divide and grow in the presence of human plasma, and second, we found that SPATEs played a central role in this process by impairing with the activation of the complement system.

microbiology↗