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David Lacher

11:35 a.m.-12:05 p.m., Tuesday
, PhD
Research Microbiologist
FDA / CFSAN / OARSA / DMB
Laurel, MD 20708 USA

Molecular serotyping of Escherichia coli using the FDA-ECID microarray

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 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 60 produce STEC strains showed that serology and the array identified 38% and 52% 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 100% of the produce STEC strains compared to 75% by PCR-RFLP, including six strains that were mistyped by PCR-RFLP.  These results show that the array is an effective alternative to serology and PCR-RFLP in serotyping environmental E. coli isolates.