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Updated: Jul 4, 2026
A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.
Published on: November 7, 2018
A multiple protocol to improve diagnosis and isolation of Shiga toxin-producing Escherichia coli from human stool
Daniel R Shelton1, Jeffrey S Karns, Choong H Park
1Environmental Microbial Safety Laboratory, U.S. Department of Agriculture, Animal and Natural Resources Institute, Agricultural Research Service, Beltsville, MD, USA. dan.shelton@ars.usda.gov
Abstract:
Many infections caused by Shiga toxin-producing Escherichia coli (STEC) are undiagnosed, particularly non-O157 STEC. We evaluated the use of a multiple protocol approach to improve diagnosis, isolation, and characterization of STEC strains. Among 18 presumptive STEC-positive stool samples received by the INOVA Fairfax Hospital, Falls Church, VA, in 2006, 16 were Shiga toxin positive. From these 16 stool samples, 8 O157:H7 and 5 non-O157 STEC were isolated by plating onto sorbitol MacConkey (SMAC) agar. The remaining 5 stool samples that did not yield colonies on SMAC agar plates were enriched. All enriched samples were Shiga toxin positive, and 2 O157:H7 and 1 non-O157 STEC were subsequently isolated. The 2 remaining enriched samples did not yield isolates; however, based on polymerase chain reaction (PCR) analysis, both samples contained STEC genes. Based on PCR analysis of non-O157 strains, 3 strain types were identified. Samples from 3 patients, received within 2 days of one another, had a similar gene profile-eae and stx(1) negative and stx(2) positive-suggesting that these patients were likely infected with the same strain. Our results indicate that a multiple protocol approach is necessary to reliably diagnose and isolate STEC strains, and that PCR profiling of strains could allow for more rapid identification of outbreaks.
Insights
A multi-step diagnostic approach improves the detection of Shiga toxin-producing Escherichia coli (STEC) infections, including non-O157 strains. Polymerase chain reaction (PCR) profiling aids in rapid identification and outbreak detection.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Bacteriology
Background:
- Many Shiga toxin-producing Escherichia coli (STEC) infections remain undiagnosed, especially those caused by non-O157 serotypes.
- Accurate and timely diagnosis of STEC is crucial for patient management and public health surveillance.
Purpose of the Study:
- To evaluate a multiple-protocol approach for enhancing the diagnosis, isolation, and characterization of STEC strains.
- To assess the utility of polymerase chain reaction (PCR) for identifying STEC and characterizing strains.
Main Methods:
- Analysis of 18 presumptive STEC-positive stool samples using sorbitol MacConkey (SMAC) agar plating and enrichment techniques.
- Shiga toxin testing and isolation of STEC strains.
- Polymerase chain reaction (PCR) analysis for gene profiling and strain characterization.
Main Results:
- Out of 18 samples, 16 tested positive for Shiga toxin.
- A combination of plating and enrichment successfully isolated STEC strains, including both O157:H7 and non-O157 serotypes.
- PCR analysis confirmed STEC presence in samples that did not yield isolates on SMAC agar and identified distinct non-O157 strain types, facilitating outbreak investigation.
Conclusions:
- A multiple-protocol approach is essential for reliable diagnosis and isolation of STEC.
- PCR profiling offers a rapid method for STEC strain identification and can aid in the detection of outbreaks.
