The evolution of resistant bacteria

Bacterial resistance to antibiotics is a major hurdle for fighting many infections. Numerous research efforts try to address the problem by identifying novel targets and synthesising new compounds with antimicrobial function.

Equally important, however, is understanding the evolutionary and genetic factors that drive the emergence and spread of resistant pathogens. In this context, the EU-funded 'Specificity of antibiotic resistance evolution' (SPECRESEVO) project set out to elucidate how resistance is affected during evolution and in different environments.

Partners isolated resistant bacteria experimentally using conventional protocols and subjected them to different growth conditions. Additionally, they isolated bacteria with a different history of antibiotic exposure to find that the effect of mutations associated with resistance is largely dependent on the environment and the genetic background. Therefore, we need to understand these mechanisms first before we can predict bacterial spread and minimise antibiotic resistance.

Furthermore, partners studied how resistant bacteria grow in the absence of antibiotic pressure. Resistant bacteria continued to have an increased fitness, compared to normal species, without reverting to drug sensitivity, clearly underscoring the necessity of genetic studies to identify the implicated loci. This competitive fitness was mutation-specific and also depended on the genetic background of the pathogen.

SPECRESEVO work proved the principle that experimental microbial evolution is a valid approach for determining key aspects related to antibiotic resistance. Collectively, the generated information sheds light onto the complex process of resistance-mediated fitness and suggests avenues to prohibit resistant bacterial spread. Long-term, this is expected to improve health care and minimise related costs.