Development of a high-throughput method to quantify bactericidal drug interactions

Joana Luísa Góis Valério

Key information

Authors:

Joana Luísa Góis Valério (Joana Luísa Góis Valério)

Supervisors:

Ana Rita Gontão Brochado; Miguel Nobre Parreira Cacho Teixeira (Miguel Nobre Parreira Cacho Teixeira)

Published in

November 7, 2022

Abstract

Antimicrobial resistance (AMR) has been declared one of the top ten global public health threats of the 21st century. As a promising approach to tackle AMR, combination-based treatments have been increasing over the past years. Antibiotic combinations have been extensively studied, uncovering relevant synergies and antagonisms in high-throughput screenings, but effects on long-term bacterial clearance have been overlooked — are synergistic interactions bactericidal, or bacteriostatic? With this question in mind, we propose a mass method for the quantification of killing, using time of regrowth (TRG). TRG depends on post-treatment lag time and number of organisms. Here, TRG is used to systematically quantify survival of Escherichia coli after treatment with pairwise combinations of a library of 92 compounds (mainly antibiotics, human-targeted drugs and food additives) and 3 query antibiotics (doxycycline, amikacin and ciprofloxacin), in two different concentrations each (in a total of ca. 1100 dose-drug pairs). To evaluate concentrations to use, minimal inhibitory concentration (MIC) values for 49 compounds with known antimicrobial properties were first assessed in Escherichia coli and Salmonella enterica serovar Typhimurium. Values of TRG from combinatorial treatment were compared with single-drug outcome and, as a proof-of-concept for TRG, two antagonistic interactions were identified, further analysed through the Bliss interaction model and validated with CFU plating. The resource described in this work paves the way for the development of a new in vitro systematic method of bactericidal drug interaction identification, which may ultimately lead to the discovery of new and more effective combinatorial treatments for infections.