Rapid antibiotic susceptibility testing using low-cost, commercially available screen-printed electrodes

Abstract

Antimicrobial resistance (AMR) is an issue of upmost global importance, with an annually increasing mortality rate and growing economic burden. Poor antimicrobial stewardship has resulted in an abundance and diverse range of antimicrobial resistance mechanisms. To tackle AMR effectively, better diagnostic tests must be developed in order to improve antibiotic stewardship and reduce the emergence of antibiotic resistant organisms. This study employs a low-cost, commercially available screen printed electrode modified with an agarose-based hydrogel deposit to monitor bacterial growth using the techniques of electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) giving rise to a new approach to measuring susceptibility. Susceptible and drug resistant Staphylococcus aureus strains were deposited onto agarose gel modified electrodes which contained clinically important antibiotics to establish growth profiles for each bacterial strain and monitor the influence of the antibiotic on bacterial growth. The results show that S. aureus is able to grow on electrodes modified with gel containing no antibiotic, but is inhibited when the gel modified electrode is seeded with antibiotic. Conversely, methicillin-resistant S. aureus (MRSA; the drug resistant strain) is able to grow on gel modified electrodes containing clinically relevant concentrations of antibiotic. Results show rapid growth profiles, with possible time to results for antibiotic susceptibility < 45 minutes, a significant improvement on the current gold standards of at least 1-2 days.

Development of a Rapid, Antimicrobial Susceptibility Test for E. coli Based on Low-Cost, Screen-Printed Electrodes

“…EIS was performed every 10 min and various parameters including Z at different frequencies were extracted and plotted over time. Similarly to the case with S. aureus /MRSA [ 23 ], Z at 100 kHz appeared to be the most sensitive parameter to monitor changes in bacterial growth. Figure 3 a shows growth curves ( Z at 100 kHz) of E. coli on the gel-modified electrodes for ≈5 h. The impedance traces were normalised with respect to their corresponding value at time t = 0 which allowed a clearer distinction to be observed ( Figure 3 c).…”

“…This specific shape results from the hydrophilic interaction of the hydrogel with acrylic through wall attachment. Compared to the previous dome-shaped gel formation [ 23 ], it ensures the full bacterial deposit is contained and tested. An example electrode with the gel in place before baseline data was recorded is displayed in Figure 2 c (top) and upon test support removal after an 8 h baseline measurement (below) for comparison.…”

“…Previously, EIS has been used to identify microorganisms including Staphylococcus aureus ( S. aureus ), Escherichia coli ( E. coli ) and Pseudomonas aeruginosa ( P. aeruginosa ) [ 20 , 21 , 22 ]. Discrimination between drug-susceptible S. aureus (MSSA) and the drug-resistant strain, MRSA, using low-cost, commercially available, screen-printed electrodes was shown in <45 min [ 23 ]. This work however was limited to organisms which displayed measurable growth changes before the gel-modified electrode dried out.…”

“…In this work, the concept of the gel-modified SPE [ 23 ] has been advanced by improving the measurement duration and assessing its potential for detecting a wider range of organisms. Escherichia coli is a Gram-negative bacterium commonly found in the mammalian gut and is considered part of the normal flora [ 30 ].…”

“…For example, several mycobacteria feature doubling times on the scale of several hours to days [ 34 ], and the presented test support will enable AST to be performed on these types of organisms in addition to relatively fast-growing organisms such as S. aureus, and E. coli which is shown in this paper. The test support structure also provides the added advantage of levelling the baseline compared to the previous sensor variant without the test support [ 23 ], enabling changes due to bacteria growth/antibiotic action to be more readily distinguished from the growth curves.…”