Anucleate cell blue assay: a useful tool for identifying novel type II topoisomerase inhibitors

A How-To Guide for Mode of Action Analysis of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are a promising alternative to classical antibiotics in the fight against multi-resistant bacteria. They are produced by organisms from all domains of life and constitute a nearly universal defense mechanism against infectious agents. No drug can be approved without information about its mechanism of action. In order to use them in a clinical setting, it is pivotal to understand how AMPs work. While many pore-forming AMPs are well-characterized in model membrane systems, non-pore-forming peptides are often poorly understood. Moreover, there is evidence that pore formation may not happen or not play a role in vivo. It is therefore imperative to study how AMPs interact with their targets in vivo and consequently kill microorganisms. This has been difficult in the past, since established methods did not provide much mechanistic detail. Especially, methods to study membrane-active compounds have been scarce. Recent advances, in particular in microscopy technology and cell biological labeling techniques, now allow studying mechanisms of AMPs in unprecedented detail. This review gives an overview of available in vivo methods to investigate the antibacterial mechanisms of AMPs. In addition to classical mode of action classification assays, we discuss global profiling techniques, such as genomic and proteomic approaches, as well as bacterial cytological profiling and other cell biological assays. We cover approaches to determine the effects of AMPs on cell morphology, outer membrane, cell wall, and inner membrane properties, cellular macromolecules, and protein targets. We particularly expand on methods to examine cytoplasmic membrane parameters, such as composition, thickness, organization, fluidity, potential, and the functionality of membrane-associated processes. This review aims to provide a guide for researchers, who seek a broad overview of the available methodology to study the mechanisms of AMPs in living bacteria.

5-Alkyloxytryptamines are membrane-targeting, broad-spectrum antibiotics

Antibiotic adjuvant therapy represents an exciting opportunity to enhance the activity of clinical antibiotics by co-dosing with a secondary small molecule. Successful adjuvants decrease the concentration of antibiotics used to defeat bacteria, increase activity (in some cases introducing activity against organisms that are drug resistant), and reduce the frequency at which drug-resistant bacteria emerge. We report that 5-alkyloxytryptamines are a new class of broad-spectrum antibacterial agents with exciting activity as antibiotic adjuvants. We synthesized 5-alkyloxytryptamine analogs and found that an alkyl chain length of 6-12 carbons and a primary ammonium group are necessary for the antibacterial activity of the compounds, and an alkyl chain length of 6-10 carbons increased the membrane permeability of Gram-positive and Gram-negative bacteria. Although several of the most potent analogs also have activity against the membranes of human embryonic kidney cells, we demonstrate that below the minimum inhibitory concentration (MIC)-where mammalian cell toxicity is low-these compounds may be successfully used as adjuvants for chloramphenicol, tetracycline, ciprofloxacin, and rifampicin against clinical strains of Salmonella typhimurium, Acinetobacter baumannii and Staphylococcus aureus, reducing MIC values by as much as several logs.

Antituberculosis drugs: ten years of research

Tuberculosis is today amongst the worldwide health threats. As resistant strains of Mycobacterium tuberculosis have slowly emerged, treatment failure is too often a fact, especially in countries lacking the necessary health care organisation to provide the long and costly treatment adapted to patients. Because of lack of treatment or lack of adapted treatment, at least two million people will die of tuberculosis this year. Due to this concern, this infectious disease was the focus of renewed scientific interest in the last decade. Regimens were optimized and much was learnt on the mechanisms of action of the antituberculosis drugs used. Moreover, the quest for original drugs overcoming some of the problems of current regimens also became the focus of research programmes and many new series of M. tuberculosis growth inhibitors were reported. This review presents the drugs currently used in antituberculosis treatments and the most advanced compounds undergoing clinical trials. We then provide a description of their mechanism of action along with other series of inhibitors known to act on related biochemical targets. This is followed by other inhibitors of M. tuberculosis growth, including recently reported compounds devoid of a reported mechanism of action.

A 4-aminofurazan derivative-A189-inhibits assembly of bacterial cell division protein FtsZ in vitro and in vivo

Out of 95,000 commercially available chemical compounds screened by the anucleate cell blue assay, 138 selected hit compounds were further screened. As a result, A189, a 4-aminofurazan derivative was found to inhibit FtsZ GTPase with an IC(50) of 80 mug/ml and to exhibit antibacterial activity against Staphylococcus aureus and Escherichia coli. Light scattering demonstrated that A189 inhibited FtsZ assembly in vitro, and microscopic observation of A189-treated E. coli indicated that A189 perturbed FtsZ ring formation and made bacterial cells filamentous. However, nucleoids staining with DAPI revealed that A189 did not affect DNA replication and chromosome segregation in bacterial filamentous cells. Furthermore, A189 made sulA-deleted E. coli cells filamentous. Taken together, these findings suggest that A189 inhibits FtsZ GTPase activity, resulting in perturbation of FtsZ ring formation, which leads to bacterial cell death.