The Pandemic H 30 Subclone of Sequence Type 131 (ST131) as the Leading Cause of Multidrug-Resistant Escherichia coli Infections in the United States (2011-2012).

BACKGROUND: Extraintestinal Escherichia coli infections are increasingly challenging due to emerging antimicrobial resistance, including resistance to extended-spectrum beta-lactams and fluoroquinolones. Sequence type 131 (ST131) is a leading contributor.

METHODS: Three hundred sixty E. coli clinical isolates from across the United States (2011-2012), selected randomly from the SENTRY collection within 3 resistance categories (extended-spectrum cephalosporin [ECS]-reduced susceptibility [RS]; fluoroquinolone-resistant, ESC-susceptible; and fluoroquinolone-susceptible, ESC-susceptible) were typed for phylogroup, sequence type complex (STc), subsets thereof, virulence genotype, O type, and beta-lactamase genes. Molecular results were compared with susceptibility profile, specimen type, age, and sex.

RESULTS: Phylogroup B2 accounted for most isolates, especially fluoroquinolone-resistant isolates (83%). Group B2-derived ST131 and its H 30 subclone (divided between H 30Rx and H 30R1) predominated, especially among ESC-RS and fluoroquinolone-resistant isolates. In contrast, among fluoroquinolone-susceptible isolates, group B2-derived STc73 and STc95 predominated. Within each resistance category, ST131 isolates exhibited more extensive resistance and/or virulence profiles than non-ST131 isolates. ST131- H 30 was distributed broadly by geographical region, age, and specimen type and exhibited distinctive beta-lactamase genes. Back-calculations indicated that within the source population ST131 accounted for 26.4% of isolates overall (vs 17% in 2007), including 19.8% ST131- H 30, 13.2% ST131- H 30R1, and 6.6% each ST131- H 30Rx and non- H 30 ST131.

CONCLUSIONS: ST131- H 30, with its ESC resistance-associated H 30Rx subset, caused most antimicrobial-resistant E. coli infections across the United States in 2011-2012 and, since 2007, increased in relative prevalence by >50%. Focused attention to this strain could help combat the current E. coli resistance epidemic.