Comparison of Common Enrichment Broths Used in Diagnostic Laboratories for Shiga Toxin-Producing Escherichia coli

Michael Bording-Jorgensen; Hannah Tyrrell; Colin Lloyd; Linda Chui

doi:10.3390/microorganisms9030503

Comparison of Common Enrichment Broths Used in Diagnostic Laboratories for Shiga Toxin-Producing Escherichia coli

Microorganisms. 2021 Feb 27;9(3):503. doi: 10.3390/microorganisms9030503.

Authors

Michael Bording-Jorgensen¹, Hannah Tyrrell¹, Colin Lloyd¹, Linda Chui^{1

2}

Affiliations

¹ Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, AB T6G 2R3, Canada.
² Alberta Precision Laboratories-Public Health Laboratory (ProvLab), Edmonton, AB T6G 2J2, Canada.

Abstract

Acute gastroenteritis caused by Shiga toxin-producing Escherichia coli (STEC) affects more than 4 million individuals in Canada. Diagnostic laboratories are shifting towards culture-independent diagnostic testing; however, recovery of STEC remains an important aspect of surveillance programs. The objective of this study was to compare common broth media used for the enrichment of STEC. Clinical isolates including O157:H7 as well as non-O157 serotypes were cultured in tryptic soy (TSB), MacConkey (Mac), and Gram-negative (GN) broths and growth was compared using culture on sheep's blood agar and real-time PCR (qPCR). In addition, a selection of the same isolates was spiked into negative stool and enriched in the same three broths, which were then evaluated using culture on CHROMagar^TM STEC agar and qPCR. TSB was found to provide the optimal enrichment for growth of isolates with and without stool. The results from this study suggest that diagnostic laboratories may benefit from enriching STEC samples in TSB as a first line enrichment instead of GN or Mac.

Keywords: STEC; broth; culture; enrichment; real-time PCR.