Rapid antimicrobial susceptibility profiling using impedance spectroscopy.

The present antibiotic susceptibility testing (AST) techniques based on bacterial culture, gene amplification and mass spectrometry are highly time consuming, labour intensive or expensive. Impedance spectroscopy is an emerging tool for rapid bacterial analysis as it is label-free, real-time, affordable and high-throughput. The over-reliance of this technique on complex chip designs and cell enrichment strategies has, however, slowed its foray into clinical AST. We demonstrate a label-free approach in which a low conductivity zwitterionic buffer is used for boosting impedance sensitivity in simple interdigitated electrodes (IDEs) allowing rapid AST in just 20 min without any liquid flow, biofunctionalization or cell enrichment steps. The detection principle relies on measuring changes in solution resistance due to antibiotic-induced bacterial cell death or growth. While the death-based approach is faster (20 min), it's restricted to surface-acting bactericidal antibiotics. The cell growth approach is longer (60-80 min) but more versatile as it applies to all drug types. Results for antibiotic sensitivity analysis and minimum inhibitory concentration (MIC) determination are illustrated for Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus against a wide class of antibiotics (penicillins, cephalosporins, polymyxins, carbapenems etc.).

ε-Polylysine Nanoconjugates: Value-Added Antimicrobials for Drug-Resistant Bacteria.

Antimicrobial resistance poses a serious threat to human health and is evidently not restricted to any one part of the globe. Over the last few decades, no new antibiotics have been discovered, and many antibiotics currently available are failing against several critical pathogenic strains due to emerging drug resistance. We have designed a strategy to combat deadly drug-resistant bacteria by using nanocargos that consist of gold nanoparticles (AuNPs) conjugated to ε-polylysine (PLL) and octadecanethiol (C18) either alone or in combination. These nanocargos when tested against reference strains of carbapenem-resistant Acinetobacter baumannii (CRAB) and methicillin-resistant Staphylococcus aureus (MRSA) showed 15-20-fold higher antibacterial activity compared to free PLL. The minimum inhibitory concentration (MIC) of the nanoconjugates was found to lie between 8 and 15 µg/mL for both these bacteria, and they were also found to be nonhemolytic and nontoxic to mammalian cells. The mechanistic evaluation of antibacterial action showed alternate pathways of uptake for free PLL and the nanoconjugates. Further, the nanocargos were successfully used and found to be superior to free PLL in preventing biofilm formation in MRSA and CRAB. The PLL nanoconjugates may find applications in prevention of bacterial biofilm formation on surfaces such as surgical instruments and indwelling devices like stents, catheters, cannulas, orthopedic implants, and pacemakers.