Do antibiotics in the environment lead to resistance in situ?

This 4-year PhD project is aiming to provide robust evidence for a causative relationship between environmental antibiotic concentrations selecting for resistance in situ.

It is funded by the Biotechnology and Biological Sciences Research Council and pharmaceutical company AstraZeneca.

By conducting experiments in synthetic and semi-naturalistic environments, and in single host backgrounds as well as complex bacterial communities, the research is seeking to determine if low antibiotic concentrations select for in situ resistance.

Resistance gene dissemination, fixation and co-selection will be investigated in order to design novel assays that can be used to determine effect concentrations of antibiotics, and implement an environmental risk assessment of antibiotics as micro pollutants.

It’s hoped the study’s findings will have direct implications for future drug development.

Most antibiotics are not fully metabolised by humans or animals. They are also not fully degraded in waste water treatment plants or sewage treatment plants, and natural degradation varies greatly between drugs.

Combined with this persistence, their excessive use as therapeutics, prophylactics and growth promoters has led to their accumulation in the natural environment, albeit at very low concentrations of ng up to ug/l.

Until recently, it was assumed antibiotic resistance would not be selected for in the environment, as environmental concentrations of antibiotics are, on the whole, far below the minimum inhibitory concentration (MIC – the concentration at which bacterial growth is inhibited).

However, Gullberg et al showed the minimal selective concentration to be as low as ng/l, a concentration expected be found in the environment but also greatly below the MIC of the drug tested. Additionally, many studies have found connections between levels of resistance and antibiotic concentrations in a variety of environments.