Understanding the evolution of antibiotic resistance in a One Health context: does resistance evolve differently across bacterial species?

Antibiotic resistance is a true One Health issue that affects humans, animals and other habitats, and therefore a threat to global health. The use of antibiotics in one area such as the clinical use might well have an impact or unintended consequences in other sectors such as environment and animal microbiome. Therefore, it is important to investigate the impact of de novo mutations on antibiotic resistance evolution when under the pressure of antibiotic use in order to tackle this issue and characterise the path of antibiotic resistance evolution.


The current study aims to investigate the reduction in susceptibility and the development of resistance against gentamicin and levofloxacin using antibiotic resistance growth plates (ARGP),“Chunking methods” and soil microcosm models. These antibiotics were chosen as model compounds, since their mechanisms of action are well studied as well as bacterial mechanisms to resist them. Therefore, it was important to compare the reported mechanisms and the current findings to test the validity of the methods and the reproductivity of the findings. These methods were utilised to study the genetic mutations that bacteria acquired after growth under different concentrations of antibiotics (0.5XMIC - 10XMIC); MIC is the minimum inhibitory concentration. Whole genome sequencing showed that different bacterial species developed different mutations under the same antibiotic pressure, bacteria in the soil developed different mutations from those developed in the ARGP and Chunking models. These mutations conferred resistance to gentamicin and were classified into four groups: rRNA, fusA gene, transport system and “other” mutations. Resistance to levofloxacin was characterised by mutations in different gene groups; DNA gyrase and DNA topoisomerase IV group and the transport system group. This study also examined phenotypic changes observed in the resistant mutants. Gentamicin resistance showed no effect on the ability of resistant isolates in antibiotic free media to form biofilms but reduced biofilm activity was seen when antibiotics were present. Differences were also observed with desiccation tolerance in the mutant isolates when compared to parent strains.


Virulence testing revealed differences in the activity of the bacterial strains such as DNase and protease; this was dependant on the mutational events they had and varied widely across the panel of organisms tested. Bioinformatic tools revealed the modelled effects of the mutations discovered in the elongation factor G in disrupting the binding between gentamicin and its target site, and the molecular docking of the mutated DNase gyrase and topoisomerase IV explained the levofloxacin resistant phenotypes of the mutants through the reduction noticed in the binding energy of levofloxacin and its target sites. This study is a step towards undertaking further research into resistance evolution in the environment and its potential impact in a One Health context.