Virus study seeks improved detection method and sanitizer efficacy data
March 2, 2021
Although some of the results will be specific to the three collaborating produce processing facilities, she said much of the research will be applicable to operations worldwide.
• Research into detecting and mitigating enteric viruses in produce settings lags behind that for bacterial pathogens.
• Researchers seek an improved testing method to analyze wash water for enteric viruses.
• Project will examine whether coliphages – viruses that infect E. coli – can be used as a reliable indicator of enteric viruses.
• Trials will examine contact times and concentrations of common sanitizers on enteric viruses and phages.
“We hope to have two different findings that may help the industry,” Sánchez said. “On one hand, we will have a method that will help producers to analyze the quality of the wash water, with a particular emphasis on the viral load. On the other hand, we will try to establish potential relationships between potential indicators, such as bacteriophages, and the load of enteric viruses. We will use mathematical models to help us on establishing this relationship.”
“The approach we are following in the three selected processing facilities can be extrapolated to any facility, mostly if they are working with the same fresh produce matrices such as leafy greens, peppers and tomatoes. We will also know the efficacy of sanitizers that they usually apply in processing and packing plants.”
Joining her are co-principal investigators Ana Allende, Ph.D., and Maria I. Gil, Ph.D., both at the Centro de Edafología y Biología Aplicada del Segura (CEBAS) in Murcia, Spain. Sánchez, a virologist by training, said Allende and Gil bring expertise in the characterization of water as well as produce sanitation.
Of the enteric viruses, norovirus is the most common one associated with produce consumption and foodborne outbreaks. Although they don’t replicate on produce, enteric viruses pose risks in two ways. The infectious dose is very low, meaning someone only has to consume a few virus particles to be sickened. In addition, enteric viruses have a high degree of environmental stability and are more tolerant to commonly used sanitizers than are pathogenic bacteria.
One of the challenges is that even if molecular-based testing confirms the presence of viral genome, it can’t discriminate whether the virus is active and potentially infectious or inactive and noninfectious.
“There are various technical issues to detect them – it’s been quite difficult to work with viruses,” Sánchez said. “That’s one of the main reasons we didn’t pay that much attention until the last few years.”
To that end, the researchers examined the effectiveness of markers incorporated into qPCR-based testing methods to assess the infectivity of enteric viruses. Once they validated sample collection and testing in a laboratory setting, they used it to assay wash water samples collected monthly in three produce processing facilities.
“The water we are using even in the lab experiments is not being generated in the lab – it’s the water coming from the processing facilities as a result of the strong collaboration with them and the great interest on this topic,” Sánchez said. “Working under real conditions gives us a real picture of the quality of the water used in their facilities. And we can perform the experiments in a manner that is close to reality when transferring our results.”
The researchers also plan to examine whether coliphages – viruses that infect E. coli – can be used as reliable indicators of potential contamination because they can mimic enteric viruses.
“We know that fecal bacteria are not good indicators of viruses,” Sánchez said. “One option is to use phages as a fecal virus indicator because their structure is pretty similar to human enteric viruses. We’ll use these in parallel to see if we can correlate viruses and the phages in wash water.”
In addition, the researchers plan to evaluate the efficacy of common sanitizers used in processing facilities as well as establish operational conditions and critical parameters for each system to inactive enteric virus and coliphages. The three sanitizers to be tested are chlorine, peracetic acid and chlorine dioxide.
Initially, the researchers inoculated water samples from the processing facilities with enteric viruses and phages to gauge inactivation by sanitizer concentrations and contact times.
The next step will be to conduct similar experiments at a pilot plant at CEBAS that uses higher volumes of process wash water and a dynamic system to represent commercial conditions.