Cefixime-tellurite rhamnose MacConkey agar for isolation of Vero cytotoxin-producingEscherichia coliserogroup O26 from Scottish cattle and sheep faeces

Abstract

To compare rhamnose MacConkey agar supplemented with cefixime and tellurite (CT-RMac) and tryptone bile X-glucuronide (TBX) agars as isolation media for Vero cytotoxin-producing Escherichia coli (VTEC) serogroup O26 from animal faeces. Nine VTEC O26 were isolated from sheep faeces; out of which six were isolated only on CT-RMac and one was isolated only on TBX. One hundred and twelve VTEC O26 were isolated from calf faeces; out of which 97% were from CT-RMac and 52% were from TBX. In a study of E. coli O26 strains, 84% of VT-positive O26 did not ferment rhamnose when compared with 16% of VT-negative O26. VT-positive (19%) and VT-negative (39%) E. coli O26 strains did not grow on CT-RMac agar. It is important to consider that VTEC O26 strains either may ferment rhamnose or may be sensitive to the CT supplement of CT-RMac agar. This work compares CT-RMac and TBX agars as isolation medium for VTEC O26 from Scottish animal faeces and highlights that VTEC O26 may be missed if only CT-RMac agar is used.