Epidemic Emergence in the United States of Escherichia coli Sequence Type 131- H 30 (ST131- H 30), 2000 to 2009

Abstract

The H30 subclone of Escherichia coli sequence type 131 (ST131) has become the leading antimicrobial-resistance E. coli lineage in the U.S., and often exhibits resistance to one or both of two key antimicrobial classes for treating Gram-negative infections, extended-spectrum cephalosporins (ESCs) and fluoroquinolones (FQs). However, the timing of and reasons for its recent emergence are inadequately defined. Accordingly, from E. coli clinical isolates collected systematically across the U.S. by the SENTRY Antimicrobial Surveillance Programs in 2000, 2003, 2006, and 2009, 234 isolates were selected randomly, stratified by year, within three resistance categories: (i) ESC-reduced susceptibility, regardless of FQ phenotype (hereafter, ESC-RS), (ii) FQ-resistant, ESC-susceptible (hereafter, FQ-R), and (iii) FQ-susceptible, ESC-susceptible (hereafter, FQ-S). Susceptibility profiles, phylogroup, ST, ST131 subclone, and virulence genotypes were determined, and temporal trends and between-variable associations were assessed statistically. From 2000 to 2006, concurrently with the emergence of ESC-RS and FQ-R strains, (virulence-associated) phylogroup B2's prevalence among such strains also rose dramatically, due entirely to rapid emergence of ST131, especially H30. By 2009, H30 was the dominant E. coli lineage overall (22%), accounting for a median of 43% of all single-agent and multidrug resistance (68% for ciprofloxacin). H30's emergence increased the net virulence gene content of resistant (especially FQ-R) isolates, giving stable overall virulence gene scores despite an approximately four-fold expansion of the historically-less-virulent resistant population. These findings define more precisely the timing and tempo of H30's emergence in the U.S., identify possible reasons for it, and suggest potential consequences, including more frequent and/or aggressive antimicrobial-resistant infections.