Non-Melibiose Fermentation and Tellurite Resistance by Shigatoxigenic and Enteropathogenic O80:H2 from Diseased Calves: Comparison with Human Shigatoxigenic O80:H2.

Despite their prevalence in Europe, the source of contamination of humans by Attaching-Effacing Shigatoxigenic (AE-STEC) O80:H2 remains unidentified. This study aimed to assess a procedure based on non-melibiose fermentation and resistance to tellurite to isolate AE-STEC and enteropathogenic (EPEC) O80:H2 from healthy cattle. The genome sequences of 40 calf and human AE-STEC and EPEC O80:H2 were analyzed: (i) none harbored the operon, but the DNA sequence instead; (ii) the -type 1 operon was detected in 16 EPEC and or AE-STEC, while no -type 1 operon was detected in the remaining 24 EPEC and AE-STEC. The 21 calf AE-STEC and EPEC O80:H2 were tested phenotypically: (i) none fermented melibiose on melibiose-MacConkey agar plates; (ii) ten of the 11 -type 1-positive strains had Minimal Inhibitory Concentrations (MIC) ≥ 128 µg/mL to potassium tellurite; (iii) conversely, the ten -negative strains had MIC of two µg/mL. Accordingly, enrichment broths containing two µg/mL of potassium tellurite and inoculated with one high MIC (≥256 µg/mL) AE-STEC O80:H2 tested positive with the O80 PCR after overnight growth, but not the enrichment broths inoculated with one low MIC (two µg/mL) EPEC. Nevertheless, neither AE-STEC nor EPEC O80:H2 were recovered from 96 rectal fecal samples collected from healthy cattle at one slaughterhouse after overnight growth under the same conditions. In conclusion, this procedure may help to isolate and AE-STEC and EPEC O80:H2, but not AE-STEC that are tellurite sensitive, and new surveys using different procedures are necessary to identify their animal source, if any.