(347c) Toward Electrochemical Screening of Pseudomonas Aeruginosa Antibiotic Susceptibility

The emergence of antibiotic resistant bacteria is driving the need for novel antibiotics and new means of efficiently screening the efficacy of potential drug targets. Current antibiotic screening relies on overnight culturing of bacteria after exposure to the antibiotic. The health of the resulting biofilm is then typically measured by the production of fluorescent proteins or staining. As an alternative approach, we propose to utilize a microfluidic platform as a small volume assay to quantify bacterial susceptibility. Further, we plan to detect the electrical response of secreted electro-active molecules by the bacteria as they are exposed to antibiotics. It is expected that if the antibiotic being studied negatively impacts the growth of the biofilm then the production and excretion of electro-active molecules will decrease.

Pseudomonas aeruginosa, a common cause of nosocomial infections, represents a serious threat to immune compromised patients due to its resistance to several antibiotics and is often used as a model organism in biofilm studies.  P. aeruginosa is an effective opportunistic pathogen in part due to the blue-green electro-active molecule, pyocyanin, that it continuously excretes. Pyocyanin production is up regulated with the production of biofilm.

In this study, P. aeruginosa biofilms were grown in polydimethyl siloxane (PDMS) microfluidic channels that were irreversibly bonded to disposable three electrode cells (EDAQ). Varying concentrations of P. aeruginosa cells in trypticase soy broth were loaded into the channels and cultured at room temperature (approximately 25^oC). Fresh trypticase soy broth was continually flowed through the channel (approximately 100 nL/min via a syringe pump) providing a constant supply of nutrients to the cells. The pyocyanin concentration in the microfluidic chamber was measured over the course of several days by scanning potentials from -0.5 to 0 V versus a silver/silver chloride reference electrode via square wave voltammetry at a frequency of 15 Hz and amplitude voltage of 0.05 volts. It has been shown that the only electro-active molecule excreted by P. aeruginosa in this potential window is pyocyanin.  An increase in the current signal at the oxidation potential of pyocyanin was observed over time signifying the growth of P. aeruginosa within the channel. Since the production of pyocyanin is correlated with the growth of P. aeruginosa cultures, this experimental approach can be used to quantitatively screen whether drug targets effectively disrupt biofilm formation in P. aeruginosa cultures. The use of a microfluidic setup with electrochemical detection allows for faster detection in a more realistic microbial environment.