Selective compartments and antibiotic resistance diversity

Abstract

Genetic variability – which selection acts upon – is a prerequisite for every evolutionary event. Selection, such as antibiotic pressure, usually reduces the diversity of variants by favoring those that are better adapted. However, the recent study of Low et al. [1xProtected environments allow parallel evolution of a bacterial pathogen in a patient subjected to long-term antibiotic therapy. Low, A.S. et al. Mol. Microbiol. 2001; 42: 619–630Crossref | PubMed | Scopus (25)See all References[1] shows that, in the long term, antibiotic treatment might provoke the diversification of antibiotic resistance.Low et al. observed that extended antibiotic therapy in a single patient suffering from multiple liver cysts infected with Escherichia coli resulted in diversification of the antibiotic resistance. The patient was treated with different β-lactam antibiotics combined with antibiotics from other classes. After several years, E. coli isolates showed greater antibiotic resistance, partly as a consequence of mutations in the promoter region of the ampC gene leading to increased expression of the AmpC enzyme. They also encoded different β-lactamases, with different pI values. The isolates differed in their auxotrophic markers. However, molecular analysis of different isolates demonstrated that they evolved from a single founder population.It is therefore possible that a single localized infection led to a range of antibiotic-resistant lineages via parallel pathways of evolution. Infected cysts probably provided separated protected environments. Consequently, separate environments allow independent evolution of resistant bacteria. In different selective compartments, antibiotics could have reached a variety of concentrations and therefore selected for different antibiotic-resistant variants. This study provides a new insight into the origins, and the maintenance, of genetic diversity in the mechanisms involved in antibiotic resistance.