Abstract
Among US veterans in 2011,
Escherichia coli
ST131, primarily its
H
30 subclone, accounted for most antimicrobial-resistant
E. coli
clinical isolates and was the dominant
E. coli
strain overall. Possible contributors included multidrug resistance, extensive virulence gene content, and ongoing transmission.
Background.
Escherichia coli
sequence type 131 (ST131), typically fluoroquinolone-resistant (FQ-R) and/or extended-spectrum β-lactamase (ESBL)–producing, has emerged globally. We assessed its prevalence and characteristics among US veterans.
Methods.
In 2011, 595 de-identified
E. coli
clinical isolates were collected systematically within 3 resistance groups (FQ-susceptible [FQ-S], FQ-R, and ESBL-producing) from 24 nationally distributed Veterans Affairs Medical Centers (VAMCs). ST131 and its
H
30 subclone were detected by polymerase chain reaction and compared with other
E. coli
for molecular traits, source, and resistance profiles.
Results.
ST131 accounted for 78% (184/236) of FQ-R and 64.2% (79/123) of ESBL-producing isolates, but only 7.2% (17/236) of FQ-S isolates (
P
< .001). The
H
30 subclone accounted for ≥95% of FQ-R and ESBL-producing, but only 12.5% of FQ-S, ST131 isolates (
P
< .001). By back-calculation, 28% of VAMC
E. coli
isolates nationally represented ST131. Overall, ST131 varied minimally in prevalence by specimen type, inpatient/outpatient source, or locale; was the most prevalent ST, followed distantly by ST95 and ST12 (13% each); and accounted for ≥40% (β-lactams), >50% (trimethoprim-sulfamethoxazole , multidrug), or >70% (ciprofloxacin, gentamicin) of total antimicrobial resistance. FQ-R and ESBL-producing ST131 isolates had higher virulence scores than corresponding non-ST131 isolates. ST131 pulsotypes overlapped extensively among VAMCs.
Conclusions.
Among US veterans, ST131, primarily its
H
30 subclone, accounts for most antimicrobial-resistant
E. coli
and is the dominant
E. coli
strain overall. Possible contributors include multidrug resistance, extensive virulence gene content, and ongoing transmission. Focused attention to ST131, especially its
H
30 subclone, could reduce infection-related morbidity, mortality, and costs among veterans.
