Prevalent combination of virulence and plasmidic-encoded resistance in ST 131 Escherichia coli strains

Escherichia coli ST131 is an important cause of multidrug-resistant infections. Thus, the aim of this study was to evaluate the concomitant presence of resistance plasmids and pathogenicity islands (PAIs) in ST131 E. coli. From 97 extra-intestinal E. coli characterized for antimicrobial susceptibility and extended-spectrum -lactamase production, 16% of isolates were identified as CTX-M-15 producers. These strains were studied by PFGE, MLST, and phylogroups, plasmid groups, PAIs, and plasmid-mediated quinolone-resistance determinants. MLST identified one ST10 strain from phylogroup A and the remaining isolates were ST131, from group B2. Despite the genetic variability, 64% of ST131 strains presented a profile composed by PAI IV536, PAI I-CFT073, and PAI IICFT073, IncF plasmid, bla(CTX-M-15), and aac(6')-lb-cr genes. The prevalent virulence and resistance profile detected among the strains may constitute an optimal combination of factors, which allow E. coli ST131 to maintain both features becoming concomitantly virulent and extremely resistant.