With spinach, it may be what鈥檚 on the inside that counts
As investigators narrow the search for the source of E. coli-tainted spinach to just a few farms in three California counties, researchers suggest it may be just as important to examine how the plants acquired and carried the bacteria as it is to find the original point of contamination.
Conventional wisdom holds that harmful bacteria on fruits and vegetables are the remnants of contamination skulking on the exterior of the plants 鈥� easily washed away by conventional surface sterilization techniques. But University of Florida microbiology experts believe the recent rash of spinach-related E. coli infections may be instead linked to swarms of the pathogen lurking inside the leafy greens.
Eric Triplett, professor and chair of microbiology and cell science with UF鈥檚 Institute of Food and Agricultural Sciences, has previously shown bacteria that wreak havoc in the human body can peacefully coexist in a plant鈥檚 system 鈥� and sometimes at levels that can reach 10,000 cells of bacteria per gram of vegetable matter. That鈥檚 far beyond what is required to make a human very ill when it comes to pathogens such as salmonella and E. coli.
鈥淲e know that plants can take bacteria up from the soil through their roots,鈥� Triplett said. 鈥淲hat we need to do now is investigate whether this is a problem with our crops, and then what we can do about it if it is.鈥�
For food safety experts, this could mean a paradigm shift in thought about food sterilization.
鈥淲hen I was a graduate student, we were taught that the insides of plants were sterile,鈥� said Michael Doyle, director of the Center for Food Safety at the University of Georgia. 鈥淔urther elucidation is needed before we can say this is a major health concern鈥ut assuming E. coli is getting into the plant 鈥� yes, this will be a big problem to address.鈥�
The problem, UF researchers say, would be twofold. The first is the question of how to keep dangerous bacteria out of water and soil in the first place. The second is how to eliminate a pathogen if it does infiltrate crops.
鈥淕iven the relatively low frequency of these types of outbreaks, I鈥檇 say the USDA and our growers are doing a pretty good job of keeping bacteria in check,鈥� Triplett said. 鈥淏ut outbreaks like this happen every one to two years, and everyone is kind of left scratching their heads.鈥�
Produce such as spinach is typically washed in a solution of chlorine and water. But this does nothing to affect the interior bacteria. Researchers with UF鈥檚 Emerging Pathogens Initiative EPI are exploring how bacteria exist in crops and how they can be controlled. Past research has involved exploring how gaseous ozone and irradiation can be used to destroy potential interior pathogens. However, the EPI, which received $21 million in funding from the Florida Legislature this year, won鈥檛 stop there.
鈥淥ur goal is to fully explore the cause of these types of problems, vet them out fully, and then find all potential solutions, not just the obvious ones,鈥� said Doug Archer, former deputy director of the Food and Drug Administration鈥檚 Center for Food Safety and Applied Nutrition and an EPI advisory board member. We may simply be able to give the plants themselves the tools to fight infection.
鈥淚t is natural for plants to have bacteria in them, they have learned to use it in many ways to get nutrients that they have trouble getting from the soil or water,鈥� said Zhonglin Mou, a microbiologist with UF鈥檚 Emerging Pathogens Initiative. 鈥淪o, they have ways of controlling bacteria that we can use.鈥�
Mou is working with natural, non-genetically-modified-organism methods to adapt plants鈥� metabolic pathways so that their natural immune system is given a boost that can eliminate harmful bacteria. He hopes to receive a patent on his work in as little as six months.
Further work must be done to determine the health risks associated with internalized bacteria. For now, Triplett and Doyle say, the best bet is trusting in the already well established safeguards.
鈥淏ut I鈥檝e been around long enough to see that things can change as the science evolves,鈥� Doyle said. 鈥淭he old rules 鈥� that we have long gone by 鈥� no longer hold because the science supports new concepts. And this could be one.鈥�
Source: University of Florida
