Chromogenic Screening Plate Production for E. coli Increased

Production and distribution of a chromogenic screening plate for rapid detection of extended spectrum β-lactamase-producing (ESBL) organisms, such as E. coli O104, has been increased.

In the past, most outbreaks of hemolytic uremic syndrome (HUS) have been associated with E. coli O157, but the current outbreak strain belongs to the E. coli O104 serogroup. The causative strain produces Shiga toxin 2 and shows high resistance to 3rd generation cephalosporins (due to the ESBL resistance mechanism), as well as broad antimicrobial resistance to, among others, trimethoprim/sulphonamide and tetracycline.

The Oxoid (Basingstoke, England) and Remel (Lenexa, KS, USA) include culture on Oxoid brilliance ESBL agar, which gives results within 24 hours.

Dr. Roger Stephan, Institute for Food Safety and Hygiene, University of Zurich (Switzerland), suggested a diagnostic strategy based on the capability of the VTEC O104 outbreak strain to produce an ESBL. He commented, "Positive fecal samples or food enrichment cultures can be streaked onto Brilliance ESBL agar. On this medium, ESBL-producing E. coli appear as blue colonies after 24 hr. incubation. Suspect colonies will then be confirmed by [polymerase chain reaction] PCR for the vtx genes. Since the prevalence of ESBL-producing E. coli in healthy people and food items should be low, this could really improve chances to isolate the strains responsible for the positive PCR screening."

Other methods of identification include direct toxin detection using the Remel ProSpecT Shiga Toxin E. coli microplate assay; isolation on media, such as Oxoid MacConkey Agar; toxin detection using the Oxoid VTEC-RPLA kit, following growth on Oxoid brain heart infusion agar; antimicrobial susceptibility testing on Oxoid Iso-Sensitest agar or Mueller-Hinton agar with cefpodoxime combination discs and identification using the DuPont Qualicon RiboPrinter microbial characterization system.

Oxoid and Remel are brands of Thermo Fisher Scientific.

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Institute for Food Safety and Hygiene, University of Zurich