Deterministic effect of oxygen level variation on shaping antibiotic resistome

Area of Science:

• Environmental microbiology
• Molecular biology
• Public health

Background:

• Antibiotic resistance genes (ARGs) pose public health threats, exacerbated by antibiotic selective pressure.
• Sub-inhibitory antibiotics induce reactive oxygen species (ROS) dependent on dissolved oxygen (DO) levels.
• The link between ROS-mediated ARG emergence, DNA damage, and metabolic changes is not fully understood.

Purpose of the Study:

• To investigate antibiotic resistome dynamics, microbiome shifts, and pathogen distribution under varying oxygen conditions (hyperoxic, normoxic, hypoxic).
• To elucidate the molecular connection between oxygen levels, ROS production, DNA damage, and ARG emergence.
• To explore the potential of oxygen manipulation for mitigating antibiotic resistance.

Main Methods:

• Utilized lab-scale bioreactors with composite inoculums from activated sludge.
• Exposed microbial communities to hyperoxic (5-7 mg L⁻¹), normoxic (2-4 mg L⁻¹), and hypoxic (0.5-1 mg L⁻¹) conditions with spiked antibiotics.
• Employed RT-qPCR and metagenomic analysis to quantify ARGs, efflux pumps, DNA repair genes, and catalase/superoxide dismutase genes.

Main Results:

• Hyperoxic conditions (5-7 mg L⁻¹) showed increased ARG counts (100.98 ppm) and enrichment of multidrug efflux pumps (acrAB, mexAB).
• Hypoxic conditions (0.5-1 mg L⁻¹) led to decreased total ARGs (0.11 ppm) and reduced int1 abundance.
• Prevalence of priority pathogens increased significantly in hyperoxia (22.5%) but decreased in hypoxia (0.9%).
• Increased ROS (10.4 µmol L⁻¹), superoxide dismutase, and DNA repair genes were observed in hyperoxic, antibiotic-spiked conditions, suggesting oxidative stress-induced mutagenesis.
• Predominance of catalase in hypoxic conditions likely limited oxidative damage and ARG proliferation.

Conclusions:

• Oxygen levels significantly influence antibiotic resistome dynamics and pathogen prevalence.
• Hyperoxia promotes ARG enrichment and pathogen growth via oxidative stress and DNA damage.
• Hypoxia reduces ARGs and pathogens, potentially by limiting oxidative stress.
• Controlling oxygen levels presents a novel strategy for mitigating antibiotic resistance development.