Implementation of molecular screening for a more efficient Shiga toxin-producing Escherichia coli testing workflow

Area of Science:

• Microbiology
• Molecular Diagnostics
• Public Health Surveillance

Background:

• Culture-independent diagnostic tests (CIDTs) are increasingly used for rapid gastroenteritis diagnosis.
• Isolating pathogens from CIDT-positive samples remains crucial for disease surveillance.
• Shiga toxin-producing Escherichia coli (STEC) is a significant cause of bacterial gastroenteritis.

Purpose of the Study:

• To evaluate the performance of a molecular screening algorithm for STEC recovery from CIDT-positive stool specimens.
• To assess the utility of Shiga toxin (stx) gene molecular screening in enrichment broths for STEC isolation.
• To determine the impact of discontinuing cultures from molecularly negative enrichment broths on STEC surveillance.

Main Methods:

• Utilized a testing algorithm at the California Department of Public Health Foodborne & Waterborne Diseases Section (CDPH-FWDS).
• Employed molecular screening of enrichment broths for stx1 and stx2 genes using real-time PCR.
• Compared STEC recovery rates from enrichment broths with and without prior molecular screening.

Main Results:

• STEC was isolated from only 3% of enrichment broths that were negative for stx1 and stx2 by molecular screening.
• Molecular screening of enrichment broths demonstrated high utility for predicting successful bacterial isolation.
• Discontinuing cultures from stx molecular screen-negative broths resulted in significant reductions in laboratory testing time and costs.

Conclusions:

• Molecular screening of enrichment broths is an effective method to guide bacterial isolation for STEC surveillance.
• Implementing this molecular screening approach can lead to substantial laboratory efficiency gains.
• The proposed testing algorithm minimizes impact on STEC surveillance efforts while optimizing resource allocation.