Pandemic fluoroquinolone resistant Escherichia coli clone ST1193 emerged via simultaneous homologous recombinations in 11 gene loci

Global growth in antibiotic resistance is a major social and health problem. The most common mechanism of high resistance to fluoroquinolones is the sequential acquisition of 3 mutations in 2 DNA topoisomerases, GyrA and ParC. We show that Escherichia coliST1193 acquired the mutant variants of gyrA and parC not by a conventional stepwise evolution but rather all at once. This was likely a result of a single transfer of about 1 Mb of chromosomal DNA from a phylogenetically distant donor E. coli strain, followed by 11 homologous recombination events involving the transferred DNA. Thus we describe a highly effective mechanism of acquisition of antimicrobial resistance by pathogenic bacteria, which led to the emergence of pandemic E. coli clone ST1193.