Fusidic acid resistance through changes in the dynamics of the drug target

Chemical Constituents and Bioactivities of the Plant-Derived Fungus Aspergillus fumigatus

A new bergamotane sesquiterpenoid, named xylariterpenoid H (1), along with fourteen known compounds (2-15), were isolated from the crude extract of Aspergillus fumigatus, an endophytic fungus isolated from Delphinium grandiflorum L. Their structures were elucidated mainly by extensive analyses of NMR and MS spectroscopic data. In addition, the screening results of antibacterial and cytotoxic activities of compounds 1-15 showed that compound 4 displayed antibacterial activities against Staphylococcus aureus and MRSA (methicillin-resistant S. aureus) with an MIC value of 3.12 µg/mL.

Neutrophil-targeted combinatorial nanosystems for suppressing bacteremia-associated hyperinflammation and MRSA infection to improve survival rates

There is currently no specific and effective treatment for bacteremia-mediated sepsis. Hence, this study engineered a combinatorial nanosystem containing neutrophil-targeted roflumilast-loaded nanocarriers and non-targeted fusidic acid-loaded nanoparticles to enable the dual mitigation of bacteremia-associated inflammation and methicillin-resistant Staphylococcus aureus (MRSA) infection. The targeted nanoparticles were developed by conjugating anti-lymphocyte antigen 6 complex locus G6D (Ly6G) antibody fragment on the nanoparticulate surface. The particle size and zeta potential of the as-prepared nanosystem were about 200 nm and -25 mV, respectively. The antibody-conjugated nanoparticles showed a three-fold increase in neutrophil internalization compared to the unfunctionalized nanoparticles. As a selective phosphodiesterase (PDE) 4 inhibitor, the roflumilast in the nanocarriers largely inhibited cytokine/chemokine release from the activated neutrophils. The fusidic acid-loaded nanocarriers were vital to eliminate biofilm MRSA colony by 3 log units. The nanoparticles drastically decreased the intracellular bacterial count compared to the free antibiotic. The in vivo mouse bioimaging demonstrated prolonged retention of the nanosystem in the circulation with limited organ distribution and liver metabolism. In the mouse bacteremia model, the multifunctional nanosystem produced a 1‒2 log reduction of MRSA burden in peripheral organs and blood. The functionalized nanosystem arrested the cytokine/chemokine overexpression greater than the unfunctionalized nanocarriers and free drugs. The combinatory nanosystem also extended the median survival time from 50 to 103 h. No toxicity from the nanoformulation was found based on histology and serum biochemistry. Furthermore, our data proved that the active neutrophil targeting by the versatile nanosystem efficiently alleviated MRSA infection and organ dysfunction caused by bacteremia. STATEMENT OF SIGNIFICANCE: Bacteremia-mediated sepsis poses a significant challenge in clinical practice, as there is currently no specific and effective treatment available. In our study, we have developed a novel combinatorial nanosystem to address this issue. Our nanosystem consists of neutrophil-targeted roflumilast-loaded nanocarriers and non-targeted fusidic acid-loaded nanoparticles, enabling the simultaneous mitigation of bacteremia-associated inflammation and MRSA infection. Our nanosystem demonstrated the decreased neutrophil activation, effective inhibition of cytokine release, elimination of MRSA biofilm colonies, and reduced intracellular bacterial counts. In vivo experiments showed prolonged circulation, limited organ distribution, and increased survival rates in a mouse bacteremia model. Importantly, our nanosystem exhibited no toxicity based on comprehensive assessments.

Extraintestinal Pathogenic Escherichia coli Utilizes Surface-Located Elongation Factor G to Acquire Iron from Holo-Transferrin

Extraintestinal pathogenic Escherichia coli (ExPEC) can cause systemic infections in both humans and animals. As an essential nutrient, iron is strictly sequestered by the host. Circumventing iron sequestration is a determinant factor for ExPEC infection. However, the ExPEC iron acquisition mechanism, particularly the mechanism of transferrin (TF) acquisition, remains unclear. This study reports that iron-saturated holo-TF can be utilized by ExPEC to promote its growth in culture medium and survival in macrophages. ExPEC specifically bound to holo-TF instead of iron-free apo-TF via the surface located elongation factor G (EFG) in both culture medium and macrophages. As a moonlighting protein, EFG specifically bound holo-TF and also released iron in TF. These two functions were performed by different domains of EFG, in which the N-terminal domains were responsible for holo-TF binding and the C-terminal domains were responsible for iron release. The functions of EFG and its domains have also been further confirmed by surface-display vectors. The surface overexpression of EFG bound significantly more holo-TF in macrophages and significantly improved bacterial intracellular survival ability. Our findings reveal a novel iron acquisition mechanism involving EFG, which suggests novel research avenues into the molecular mechanism of ExPEC resistance to nutritional immunity. IMPORTANCE Extraintestinal pathogenic Escherichia coli (ExPEC) is an important pathogen causing systemic infections in humans and animals. The competition for iron between ExPEC and the host is a determinant for ExPEC to establish a successful infection. Here, we sought to elucidate the role of transferrin (TF) in the interaction between ExPEC and the host. Our results revealed that holo-TF could be utilized by ExPEC to enhance its growth in culture medium and survival in macrophages. Furthermore, the role of elongation factor G (EFG), a novel holo-TF-binding and TF-iron release protein, was confirmed in this study. Our work provides insights into the iron acquisition mechanism of ExPEC, deepens understanding of the interaction between holo-TF and pathogens, and broadens further researches into the molecular mechanism of ExPEC pathogenicity.

Ribosome Protection Proteins-"New" Players in the Global Arms Race with Antibiotic-Resistant Pathogens

Bacteria have evolved an array of mechanisms enabling them to resist the inhibitory effect of antibiotics, a significant proportion of which target the ribosome. Indeed, resistance mechanisms have been identified for nearly every antibiotic that is currently used in clinical practice. With the ever-increasing list of multi-drug-resistant pathogens and very few novel antibiotics in the pharmaceutical pipeline, treatable infections are likely to become life-threatening once again. Most of the prevalent resistance mechanisms are well understood and their clinical significance is recognized. In contrast, ribosome protection protein-mediated resistance has flown under the radar for a long time and has been considered a minor factor in the clinical setting. Not until the recent discovery of the ATP-binding cassette family F protein-mediated resistance in an extensive list of human pathogens has the significance of ribosome protection proteins been truly appreciated. Understanding the underlying resistance mechanism has the potential to guide the development of novel therapeutic approaches to evade or overcome the resistance. In this review, we discuss the latest developments regarding ribosome protection proteins focusing on the current antimicrobial arsenal and pharmaceutical pipeline as well as potential implications for the future of fighting bacterial infections in the time of "superbugs."

Synthesis of Fusidic Acid Derivatives Yields a Potent Antibiotic with an Improved Resistance Profile

Fusidic acid (FA) is a potent steroidal antibiotic that has been used in Europe for more than 60 years to treat a variety of infections caused by Gram-positive pathogens. Despite its clinical success, FA requires significantly elevated dosing (3 g on the first day, 1.2 g on subsequent days) to minimize resistance, as FA displays a high resistance frequency, and a large shift in minimum inhibitory concentration is observed for resistant bacteria. Despite efforts to improve on these aspects, all previously constructed derivatives of FA have worse antibacterial activity against Gram-positive bacteria than the parent natural product. Here, we report the creation of a novel FA analogue that has equivalent potency against clinical isolates of Staphylococcus aureus (S. aureus) and Enterococcus faecium (E. faecium) as well as an improved resistance profile in vitro when compared to FA. Importantly, this new compound displays efficacy against an FA-resistant strain of S. aureus in a soft-tissue murine infection model. This work delineates the structural features of FA necessary for potent antibiotic activity and demonstrates that the resistance profile can be improved for this scaffold and target.