Novel microarray design for molecular serotyping of shiga toxin- producing Escherichia coli strains isolated from fresh produce.

Serotyping Escherichia coli is a cumbersome and complex procedure due to the existence of large numbers of O- and H-antigen types. It can also be unreliable, as many Shiga toxin-producing E. coli (STEC) strains isolated from fresh produce cannot be typed by serology or have only partial serotypes. The FDA E. coli identification (FDA-ECID) microarray, designed for characterizing pathogenic E. coli, contains a molecular serotyping component, which was evaluated here for its efficacy. Analysis of a panel of 75 reference E. coli strains showed that the array correctly identified the O and H types in 97% and 98% of the strains, respectively. Comparative analysis of 73 produce STEC strains showed that serology and the array identified 37% and 50% of the O types, respectively, and that the array was able to identify 16 strains that could not be O serotyped. Furthermore, the array identified the H types of 97% of the produce STEC strains compared to 65% by serology, including six strains that were mistyped by serology. These results show that the array is an effective alternative to serology in serotyping environmental E. coli isolates.