Escherichia coli sequence type ST131 as an emerging fluoroquinolone-resistant uropathogen among renal transplant recipients

Abstract

Among 40 Escherichia coli urine isolates from renal transplant recipients (Galveston, TX, 2003 to 2005), sequence type ST131 (O25:H4) was highly prevalent (representing 35% of isolates overall and 60% of fluoroquinolone-resistant isolates), virulent appearing, antimicrobial resistant (but extended-spectrum-cephalosporin susceptible), and associated with black race. Pulsotypes were diverse; some were linked to other locales. ST131 emerged significantly during the study period. These findings suggest that E. coli ST131 may constitute an important new multidrug-resistant threat to renal transplant recipients.

FIG. 1.

Dendrogram of PFGE profiles of 39 Escherichia coli isolates from renal transplant recipients. The dendrogram (unweighted-pair group method with averaging) was based on Dice similarity coefficients from XbaI PFGE profiles. The ST131 isolates (n = 14) (dashed rectangle and heavy branches) cluster at the 75% similarity level, connected to the non-ST131 isolates at the 58% similarity level. The tree extends to 53% similarity. The 94% similarity threshold resolved 9 PFGE types among the ST131 isolates and 25 PFGE types among the non-ST131 isolates. Vertical bars to the right of the labels link adjacent isolates with the same PFGE type. No 2 profiles were indistinguishable. Bullets, fluoroquinolone-resistant (FQ-R) isolates. The 40th isolate (non-ST131) sheared during PFGE (not shown).

FIG. 2.

Principal coordinate analysis of virulence gene data for 40 Escherichia coli isolates from renal transplant recipients. Isolates are plotted according to their values on axis 1 (horizontal) and axis 2 (vertical) of a principal coordinate analysis that included genotyping data for 65 virulence genes and variants plus phylogenetic groups. The ST131 isolates (n = 14) (open circles), from group B2, cluster in the upper-left region of the field, well separated from the non-ST131 isolates (n = 26) (closed circles), which are identified by phylogenetic group (A, B1, B2, and D). The P values for ST131 versus non-ST131 are as follows: for axis 1, 0.001, and for axis 2, <0.001 (by the 2-tailed t test).

FIG. 3.

Virulence and resistance scores in relation to ST131 status, fluoroquinolone phenotype, and phylogenetic group among 40 E. coli urine isolates from renal transplant recipients. Box-whisker plots show group medians (wide bar), 25th and 75th percentiles (bottom and top of boxes, respectively), and maximum and minimum values (heavy bars). P values were determined by the Mann-Whitney U test (2-tailed). (Left) Virulence scores among ST131 isolates, versus those among fluoroquinolone-susceptible (FQ-S) and fluoroquinolone-resistant (FQ-R) non-ST131 isolates. (Middle) Virulence scores among ST131 isolates, versus those among group B2 and other non-ST131 isolates. (Right) Resistance scores among ST131 isolates, versus those among group B2 and other non-ST131 isolates.