Why are some types of E. coli less resistant to antibiotics?

What is it about?

This paper looks at a specific type of E. coli (ST95) isolated from blood infections to try and figure out what the isolates that are not resistant to antibiotics have in common. Although ST95 E. coli are common worldwide, they are generally less likely to carry antibiotic resistance genes than many other pathogenic E. coli. By examining their genomes, we found that ST95 E. coli can be subdivided into different types, some of which (fimH-1) are commonly antibiotic resistant, while others (fimH-6) are rarely resistant. We show that fimH-6 isolates usually carry a large plasmid (pUTI89) that may prevent these bacteria from acquiring other plasmids carry drug resistance genes.

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Why is it important?

Antibiotic resistance in disease-causing bacteria is a major medical and public health problem, and we still don't understand all the factors affecting the flow and sharing of antibiotic resistance genes in bacterial populations. There are some known mechanisms by which bacteria prevent uptake of new DNA (such as plasmids that could carry antibiotic resistance genes), but so far we have found no connection between these known mechanisms and the pUTI89 plasmid. This may suggest other mechanisms for restricting plasmid/gene sharing are present, and would be worthy of further study.