gms | German Medical Science

Objectives: Bacterial antibiotic resistance is an important challenge against which the healthcare system is continually battling. Current methods to identify infectious microbes and define their sensitivity or resistance to antibiotics require two to ten days from isolation to establishment of an antibiogram.This slow process limits advances in antimicrobial drug discovery and, in the clinical context, delays both diagnostic and delivery of targeted treatment with potential devastating outcome for the patients. In this explorative prospective study, we strived to establish a faster and more sensitive method to characterize the inhibitory and/or lytic properties of antibiotics against bacterial growth, using a Scattered Light Integrated Collector (SLIC).

Methods: SLIC detects the refraction of light beamed through a particulate-containing solution. The presence of bacteria in solution refracts light and can therefore be recorded in real-time with yet unmatched sensitivity (10² CFU/mL).Using SLIC, we monitored the growth of lab strains of E. coli and S. aureus (as model of gram-negative or -positive bacteria, respectively) upon challenge with clinically relevant antibiotics. We first titrated each antibiotic to define minimal inhibitory concentrations (MICs). We controlled for off-target toxicity by challenging resistant bacterial strains and making sure no inhibitory effect could be measured at concentrations several folds over the MIC. We then designed antibiotic panels that could provide a first clue into which class of bacteria is causing an infection and define its antibiotic resistance/sensitivity profile. Finally, we tested these antibiotic panels in bacterial strains isolated from joints of orthopedic patient and grown in the laboratory.

Results and conclusion: We found that SLIC detects perturbations in bacterial growth accurately and reproducibly within minutes of culture. Indeed, we show that SLIC can be used to measure dose-dependent inhibitory or bacteriolytic activity of broad classes of antibiotics. Furthermore, our panel-design enables us to establish a profile of antibiotic sensitivity or resistance of the tested bacteria within 90 minutes. This rapid delivery of antibiogram-like data can thus provide in parallel information on the class of bacteria tested and help refine targeted drugs to block its expansion.

The constant emergence of resistant strains of bacteria pushes the pharma industry to develop better drugs. Our optimized method could significantly accelerate this work by characterizing the efficacy of new classes of compounds against bacterial viability within minutes, a timeframe far shorter than the current microbiology standards. Applied in the clinical context, this new tool would also have the potential to accelerate diagnostic processes thus not only benefitting patients by improving drug design but directly from the bedside.