Studies on simultaneous enrichment and detection of Escherichia coli O157:H7 during sample shipment

Authors: CHEN, CHUNYAN - Purdue University; CORONEL-AGUILERA, CLAUDIA - Purdue University; APPLEGATE, BRUCE - Purdue University; Gehring, Andrew; BHUNIA, ARUN - Purdue University; Paoli, George

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2022
Publication Date: 11/15/2022
Citation: Chen, C., Coronel-Aguilera, C., Applegate, B.M., Gehring, A.G., Bhunia, A.K., Paoli, G. 2022. Studies on simultaneous enrichment and detection of Escherichia coli O157:H7 during sample shipment. Foods. 11(22):3653. https://doi.org/10.3390/foods11223653.
DOI: https://doi.org/10.3390/foods11223653

Interpretive Summary: Harmful E. coli bacteria are major foodborne pathogens, causing more than 200,000 illnesses, 4,000 hospitalizations, and numerous deaths in the US each year, at an economic burden of nearly 650 million dollars. As a result, the USDA Food Safety and Inspection Service (FSIS) regularly inspects beef samples for harmful E. coli. These samples are collected by FSIS inspectors in beef processing facilities and shipped overnight to FSIS labs for pathogen detection and isolation. FSIS uses a complex and lengthy method for detection of harmful E. coli in beef involving microbiological, molecular biological, immunological, and biochemical techniques. The first step involves the select growth of harmful E. coli from beef samples for 15-24 hours in specialized microbiological culture media. Scientists from the Purdue University Center for Food Safety Engineering, in collaboration with ARS scientists in Wyndmoor, Pennsylvania, studied the efficacy of leveraging the shipping time (at least 15 hours) to grow the bacteria while simultaneously using a previously developed light-producing bacteriophage (bacterial virus) reporter system to detect harmful E. coli. Upon receipt, an FSIS lab could examine the growing sample for light production to identify presumptive positive samples. Modifications of the current FSIS detection method were evaluated (e.g., using sealed bottles rather than unsealed bags for microbial growth, reducing the ratio of ground beef to culture media, examining the bacterial growth at lower temperatures) to make the method amenable to shipping conditions. More work will need to be done to identify or engineer an inexpensive method to generate and hold an appropriate temperature for incubation during shipping. Nevertheless, the results demonstrated a potential for this method to reduce detection time by as much as 24 hours.

Technical Abstract: The USDA-FSIS regards E. coli O157:H7 as an adulterant in raw ground beef with a zero tolerance. This policy requires robust detection methods, that use an initial 15-24h enrichment. Currently FSIS collects samples from beef processing facilities and ships them overnight to their testing laboratories. This study assessed the potential of using the FV10nluc phage-based luminescence detection assay during enrichment while the sample is in transit. Parameters including phage concentrations, temperature, and media-to-sample ratios were evaluated. Experiments in liquid media tested phage concentrations (102-105 pfu/mL) and time-to-detection with E. coli O157:H7 from 2 to 2x10^5 CFU/sample. Results showed that 1.73x 10^3 pfu/mL of FV10nluc was able to detect 2 CFU in 10 h. The detection of E. coli O157:H7 was further evaluated in kinetic studies using ratios of 1:3, 1:2, and 1:1 ground beef sample to enrichment media at 37°C. All sample to media ratios yielded positive results for as little as 2-3 CFU in 325 g ground beef in about 15 h. These results suggest this approach is feasible and could allow the rapid detection of a presumptive positive upon arrival of the sample to the testing lab. However, the requirement of 37°C poses an engineering hurdle, as the shipping container would need to maintain that temperature. This limitation should be easily addressed, as the current shipping conditions require cargo holds to be maintained at Controlled Room Temperature (15-25°C). If successful, this approach could be expanded to other food samples that require enrichment for detection.