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. 2017 May 2;4(2):ofx089.
doi: 10.1093/ofid/ofx089. eCollection 2017 Spring.

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)

James R Johnson  1   2 , Stephen Porter  1   2 , Paul Thuras  1   2 , Mariana Castanheira  3
Affiliations

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)

James R Johnson et al. Open Forum Infect Dis. .

Abstract

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 H30 subclone (divided between H30Rx and H30R1) 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-H30 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-H30, 13.2% ST131-H30R1, and 6.6% each ST131-H30Rx and non-H30 ST131.

Conclusions: ST131-H30, with its ESC resistance-associated H30Rx 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.

Keywords: Escherichia coli infections; ST131.; antimicrobial resistance; extended-spectrum beta-lactamases; fluoroquinolone resistance.

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Figures

Figure 1.
Figure 1.
Phylogeny of Escherichia coli and sequence type complex (STc) 131. The phylogram is illustrative only; branch lengths are not to scale, and tree conformation is approximate. Phylogenetic groups are identified with brackets. Each STc included in the present study is labeled; unlabeled branches represent other (unstudied) STs within the indicated phylogenetic groups. Stippled rectangle, STc131; open rectangle within stippled rectangle, ST131-H30 subclone.
See this image and copyright information in PMC

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