Fluoroquinolones stimulate the DNA cleavage activity of topoisomerase IV by promoting the binding of Mg(2+) to the second metal binding site

Combination of photodynamic antimicrobial chemotherapy and ciprofloxacin to combat S. aureus and E. coli resistant biofilms

Photodynamic antimicrobial chemotherapy (PACT) coupled with an antibiotic, ciprofloxacin (CIP), was investigated using two indium metallated cationic photosensitizers, a porphyrin (1) and a phthalocyanine (2). Applying PACT followed by the antibiotic treatment led to a remarkable reduction in the biofilm cell survival of two antibiotic-resistant bacterial strains, S. aureus (Gram-positive) and E. coli (Gram-nenative). Treating both bacteria strains with PACT alone showed no significant activity at 32 µM with 15 min irradiation, while CIP alone exhibited a minimum biofilm inhibition concentration (MBIC) at 4 and 8 µg/mL on S. aureus and E. coli, respectively following 24 h incubation. The combined treatment resulted in the complete eradication of the matured biofilms with high log₁₀ reduction values of 7.05 and 7.20 on S. aureus and E. coli, respectively, at low concentrations. It was found that 15 min PACT irradiation of 8 µM of complexes (1 and 2) combined with 2 µg/mL of CIP have a 100% reduction of the resistant S. aureus biofilms. Whereas the total killing of E. coli was obtained when combining 8 µM of complex 1 and 16 µM of complex 2 both combined with 4 µg/mL of CIP.

Development of a signal-enhanced LFIA based on tyramine-induced AuNPs aggregation for sensitive detection of danofloxacin

A signal-enhanced LFIA based on tyramine (TYR)-induced AuNPs aggregation has been developed for the sensitive detection of danofloxacin (DAN). In the model, the hydroxyl radical produced by HRP catalyzing H₂O₂ can trigger the TYR-AuNPs to aggregate on the T or C line for enhancing the detection signal. The linear range of TYR-AuNPs LFIA was 0.25-5 ng mL^-1 with the limit of detection (LOD) of 0.032 ng mL^-1, and the LOD was 8-fold lower than that of the traditional AuNPs LFIA (0.26 ng mL^-1). The TYR-AuNPs LFIA could be used with the naked eyes to qualitatively detect DAN with a cut-off limit of 2.5 ng mL^-1, which was 4-fold lower than that of the traditional AuNPs LFIA (10 ng mL^-1). The recoveries of TYR-AuNPs LFIA were 86.04-105.14% and 92.41-110.19%, with the coefficient of variation of 1.71-2.05% and 4.42-5.89% in chicken and pork, respectively.

Better living through chemistry: Addressing emerging antibiotic resistance

The increasing emergence of multidrug-resistant bacteria is recognized as a major threat to human health worldwide. While the use of small molecule antibiotics has enabled many modern medical advances, it has also facilitated the development of resistant organisms. This minireview provides an overview of current small molecule drugs approved by the US Food and Drug Administration (FDA) for use in humans, the unintended consequences of antibiotic use, and the mechanisms that underlie the development of drug resistance. Promising new approaches and strategies to counter antibiotic-resistant bacteria with small molecules are highlighted. However, continued public investment in this area is critical to maintain an edge in our evolutionary "arms race" against antibiotic-resistant microorganisms. Impact statement The alarming increase in antibiotic-resistant microorganisms is a rapidly emerging threat to human health throughout the world. Historically, small molecule drugs have played a major role in controlling bacterial infections and they continue to offer tremendous potential in countering resistant organisms. This minireview provides a broad overview of the relevant issues, including the diversity of FDA-approved small molecule drugs and mechanisms of drug resistance, unintended consequences of antibiotic use, the current state of development for small molecule antibacterials and financial challenges that impact progress towards novel therapies. The content will be informative to diverse stakeholders, including clinicians, basic scientists, translational scientists and policy makers, and may be used as a bridge between these key players to advance the development of much-needed therapeutics.

DNA Topoisomerases as Targets for Antibacterial Agents

DNA topoisomerases are proven therapeutic targets of antibacterial agents. Quinolones, especially fluoroquinolones, are the most successful topoisomerase-targeting antibacterial drugs. These drugs target type IIA topoisomerases in bacteria. Recent structural and biochemical studies on fluoroquinolones have provided the molecular basis for both their mechanism of action, as well as the molecular basis of bacterial resistance. Due to the development of drug resistance, including fluoroquinolone resistance, among bacterial pathogens, there is an urgent need to discover novel antibacterial agents. Recent advances in topoisomerase inhibitors may lead to the development of novel antibacterial drugs that are effective against fluoroquinolone-resistant pathogens. They include type IIA topoisomerase inhibitors that either interact with the GyrB/ParE subunit or form nick-containing ternary complexes. In addition, several topoisomerase I inhibitors have recently been identified. Thus, DNA topoisomerases remain important targets of antibacterial agents.