Production of Shiga toxin by Shiga toxin-expressing Escherichia coli (STEC) in broth media: from divergence to definition.

Aims: To determine the suitability of eight different commercial broth media for Shiga toxin (Stx) production. Methods and Results: Shiga toxin-producing Escherichia coli (STEC) strains producing Stx1 or Stx2 were grown at 37°C (250 rev min−1) for 24 h in brain heart infusion broth, E. coli broth, Evans medium, Luria-Bertani broth, Penassay broth, buffered-peptone water, syncase broth and trypticase soy broth. Toxin production was measured by enzyme-linked immunosorbent assay (ELISA) in polymyxin-treated cell pellets and/or supernatants of cultures, ELISA optical densities reached 1 when isolates were grown for 2–4 h in E. coli broth in the presence of antibiotic. Besides, a collection of STEC-expressing Stx strains was evaluated and the Stx production was assayed in the supernatants and in polymyxin-treated pellets of bacterial growth after 4 h of cultivation in E. coli broth in the presence of antibiotic. Conclusions: The most suitable medium for Stx production was E. coli broth when the bacterial isolates were grown for 4 h in the presence of ciprofloxacin and the Stx production is detected in the supernatant. Significance and Impact of the Study: This study presents the first comprehensive comparison of different broth media with regard to Stx production to establish optimal culture conditions for STEC detection in routine diagnostic laboratories. [ABSTRACT FROM AUTHOR]