Continuous culture of Escherichia coli, under selective pressure by a novel antimicrobial complex, does not result in the development of resistance

Antibiotic resistance is a major global health problem. Preservation of antibiotics, underpinned by the availability of novel antimicrobials that avoid the emergence of antimicrobial resistance and antibiotic cross-resistance is an important societal goal. We have developed a novel biocidal complex (iodo-thiocyanate complex or ITC), drawing the inspiration from naturally occurring peroxidase-catalysed systems. This study was aimed to reveal the potential of ITC for induction of resistance and cross-resistance, and, thus, different aspects of resistance were explored. We show that the repeated exposure of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and methicillin-resistant S. aureus to sub-inhibitory levels of ITC during serial passage of batch cultures did not generate ITC resistance. By comparison, E. coli and S. aureus developed low-level and high-level resistance to levofloxacin (LVX), respectively. Further, we attempted to generate de novo resistance in antimicrobial-sensitive E. coli during 20 days of continuous culturing when exposed to gradually increasing concentrations of ITC and LVX. The exposure of E. coli to ITC did not induce resistance to ITC, or cross-resistance to LVX. No distinct mutational pattern was evidenced from whole-genome sequence (WGS)-based analysis of ITC-challenged bacterial populations. By contrast, the resistance to LVX was rapidly induced, selected for high-level and enriched with a distinctly characteristic genome mutational pattern. WGS of LVX-challenged population revealed that the majority of mutations appeared in the genes of LVX target proteins and drug influx. This study suggests that the usage of ITC may not trigger the emergence of facile resistance or cross-resistance, in contrast to common antibiotics.