Antibiotic susceptibility testing at a screen-printed carbon electrode array

Abstract

Screen-printed carbon electrode arrays were treated to allow respiratory activity-based measurement of antibiotic susceptibility with Escherichia coli JM105. Carbon working electrodes were examined for antibiotic adsorption and were pretreated with various electrochemical and chemical protocols to minimize antibiotic adsorption. Treatment by voltammetry in basic solution or by chemical modification with poly-L-lysine or chitosan were found to be effective methods for the elimination of adsorption of the studied group of 17 antibiotics, which comprised several classes and modes of action. Measurements consisted of two-electrode amperometry of the bacterial suspension after 10 min of incubation with antibiotic followed by addition of an oxidative cocktail of ferricyanide and dichlorophenolindophenol for a further 10 min; response currents, which indicate the extent of reduction of ferricyanide to ferrocyanide by cellular respiratory activity, decrease with increasing concentration of antibiotic present in the initial 10 min incubation. IC50 values obtained for chloramphenicol with these electrode modification methods are consistent at 2.0 +/- 0.2 mM, in approximate agreement with previously reported respiration-based results for this organism but significantly higher than values reported for growth-based antibiotic susceptibility testing methods.