P1-129 Characterization of Shiga Toxin-producing Escherichia coli O5 Strains Received at CDC from 2011–2012

Monday, July 29, 2013
Exhibit Hall (Charlotte Convention Center)
Haley Martin, Centers for Disease Control and Prevention, Atlanta, GA
Devon Stripling, Centers for Disease Control and Prevention, Atlanta, GA
Lauri Lindberg, Centers for Disease Control and Prevention, Atlanta, GA
Evangeline Sowers, Centers for Disease Control and Prevention, Atlanta, GA
Sung Im, Centers for Disease Control and Prevention, Atlanta, GA
Kelley Hise, Centers for Disease Control and Prevention, Atlanta, GA
Efrain Ribot, Centers for Disease Control and Prevention, Atlanta, GA
John Besser, Centers for Disease Control and Prevention, Atlanta, GA
Peter Gerner-Smidt, Centers for Disease Control and Prevention, Atlanta, GA
Nancy Strockbine, Centers for Disease Control and Prevention, Atlanta, GA
Introduction: Laboratory surveillance for STEC is essential for identifying clusters to detect outbreaks and for monitoring trends to assess the impact of interventions and policy.  Unusual phenotypic traits have the potential to negatively impact surveillance systems.  Shiga toxin-producing Escherichia coli (STEC) are typically urease negative; however, urease-producing STEC O5 strains were recently reported in Austria.     

Purpose: The purpose of this study was to characterize STEC O5 strains from the United States for their virulence genes, phenotypic markers, and genetic similarity.

Methods: STEC O5 isolates submitted to CDC by state and county public health laboratories were tested by PCR for Shiga toxins 1 and 2 (stx1 and stx2), intimin (eae) and enterohemolysin (ehxA) and serotyped.  All isolates were inoculated to urea agar slants (Christensen’s) using an 18-24 hour culture.  The slants were incubated at 35-37°C and examined at 24 hours, 48 hours, and 7 days for the development of an intense pink-red color on the slant, indicating urease activity.  Genetic variation among isolates was assessed by PFGE analysis.

Results: During the past two years, CDC received 75 STEC O5 strains that were all non-motile from 29 states.  The majority of these, 70/75 (93%), hydrolyzed urea within 24 hours, and an additional strain within 48 hours, while the remaining strains showed no activity within 7 days.  73 strains (97.3%) were positive by PCR for stx1, eae, and ehxA genes, while two strains (2.7%) possessed the genes for stx1, stx2, and ehxA and one strain (1.3%) was positive for stx1, stx2, eae, and ehxA.  By PFGE analysis, 57 strains were separable into 48 unique XbaI patterns.

Significance: STEC strains typically lack urease activity.  These findings demonstrate the urelytic nature of a subset of genetically diverse STEC strains.  Continued surveillance is important to detect phenotypic variants that may impact identification schemes.