Rv0684/fusA1, an Essential Gene, Is the Target of Fusidic Acid and Its Derivatives in Mycobacterium tuberculosis

Reversing the Natural Drug Resistance of Gram-Negative Bacteria to Fusidic Acid via Forming Drug-Phospholipid Complex

Drug resistance substantially compromises antibiotic therapy and poses a serious threat to public health. Fusidic acid (FA) is commonly used to treat staphylococcal infections, such as pneumonia, osteomyelitis and skin infections. However, Gram-negative bacteria have natural resistance to FA, which is almost restrained in cell membranes due to the strong interactions between FA and phospholipids. Herein, we aim to utilize the strong FA-phospholipid interaction to pre-form a complex of FA with the exogenous phospholipid. The FA, in the form of an FA-phospholipid complex (FA-PC), no longer interacts with the endogenous membrane phospholipids and thus can be delivered into bacteria cells successfully. We found that the water solubility of FA (5 µg/mL) was improved to 133 µg/mL by forming the FA-PC (molar ratio 1:1). Furthermore, upon incubation for 6 h, the FA-PC (20 µg/mL) caused a 99.9% viability loss of E. coli and 99.1% loss of P. aeruginosa, while free FA did not work. The morphology of the elongated bacteria cells after treatment with the FA-PC was demonstrated by SEM. The successful intracellular delivery was shown by confocal laser scanning microscopy in the form of coumarin 6-PC (C6-PC), where C6 served as a fluorescent probe. Interestingly, the antibacterial effect of the FA-PC was significantly compromised by adding extra phospholipid in the medium, indicating that there may be a phospholipid-based transmembrane transport mechanism underlying the intracellular delivery of the FA-PC. This is the first report regarding FA-PC formation and its successful reversing of Gram-negative bacteria resistance to FA, and it provides a platform to reverse transmembrane delivery-related drug resistance. The ready availability of phospholipid and the simple preparation allow it to have great potential for clinical use.

The implication of Mycobacterium tuberculosis-mediated metabolism of targeted xenobiotics

Drug metabolism is generally associated with liver enzymes. However, in the case of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), Mtb-mediated drug metabolism plays a significant role in treatment outcomes. Mtb is equipped with enzymes that catalyse biotransformation reactions on xenobiotics with consequences either in its favour or as a hindrance by deactivating or activating chemical entities, respectively. Considering the range of chemical reactions involved in the biosynthetic pathways of Mtb, information related to the biotransformation of antitubercular compounds would provide opportunities for the development of new chemical tools to study successful TB infections while also highlighting potential areas for drug discovery, host-directed therapy, dose optimization and elucidation of mechanisms of action. In this Review, we discuss Mtb-mediated biotransformations and propose a holistic approach to address drug metabolism in TB drug discovery and related areas.

Mycobacterium tuberculosis-mediated metabolism of xenobiotics poses an important research question for antitubercular drug discovery. Identification of the metabolic fate of compounds can inform requisite structure–activity relationship strategies early on in a drug discovery programme towards improving the properties of the compound.

Morphology of Lymphoid Tissue in the Lungs of Guinea Pigs Infected with Mycobacterium bovis against the Background of Vaccine Immunity and the Action of Betulin and Its Derivatives

Tuberculosis caused by Mycobacterium bovis is a serious problem for animal and human health worldwide. A promising concept for the design of anti-tuberculosis drugs is the conjugation of an immunogenic fraction isolated from bacterial vaccines with a stimulating component. Taking this principle as a basis, conjugates based on BCG antigens with betulin and its derivatives (betulonic and betulinic acids) were designed. The aim of this research was to study the morphological changes in the lymphoid tissue associated with the bronchial mucosa lungs (BALT) in guinea pigs sensitized with experimental conjugates using a model of experimental tuberculosis. The results showed a significant decrease in the BALT response, expressed by a decrease in the diameter of lymphatic follicles and a decrease in their activity when exposed to conjugates based on BCG antigens with betulin and, especially, with betulonic acid, with a visually greater number of plasma cells observed in the lung tissues of guinea pigs of these groups. The absence of tuberculous foci and low BALT activity in the lungs of animals treated with betulin and betulonic acid are probably associated with the activation of humoral immunity under the action of these conjugates.

Innovation Experiences from Africa-Led Drug Discovery at the Holistic Drug Discovery and Development (H3D) Centre

As the so-called “next frontier” in global economic terms, Africa’s disease burden continues to choke and cripple economic growth across the continent. The highest burden is attributable to malaria and tuberculosis (TB), which also remain among the deadliest infectious diseases affecting mankind the world over (Malaria, 627,000 deaths; TB, 1.5 million deaths, in 2020). In achieving self-determination with respect to the health needs of all who live on the continent, Africa must align with global north efforts and be a source of health innovation. This will in part require the creation of an ecosystem of innovative pharmaceutical R&D and expanding it across the continent by scaling up through sustained performance and excellence. To this end, the Holistic Drug Discovery and Development (H3D) Centre at University of Cape Town in South Africa has risen to this challenge. Here, we highlight the innovation experiences gained at H3D, covering the advances made in our quest to contribute to a global pipeline of therapeutic interventions against malaria and TB. We discuss selected chemical series starting from their identification, structure–activity relationships, mode of action, safety, proof-of-concept studies, and lessons learned.

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.

Bioactivities and Structure-Activity Relationships of Fusidic Acid Derivatives: A Review

Fusidic acid (FA) is a natural tetracyclic triterpene isolated from fungi, which is clinically used for systemic and local staphylococcal infections, including methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci infections. FA and its derivatives have been shown to possess a wide range of pharmacological activities, including antibacterial, antimalarial, antituberculosis, anticancer, tumor multidrug resistance reversal, anti-inflammation, antifungal, and antiviral activity in vivo and in vitro. The semisynthesis, structural modification and biological activities of FA derivatives have been extensively studied in recent years. This review summarized the biological activities and structure-activity relationship (SAR) of FA in the last two decades. This summary can prove useful information for drug exploration of FA derivatives.