Wednesday, June 12, 2013


Contrary to the strong belief that plant foods are less vulnerable to contamination with bacteria and virus, an analysis of food poisoning episodes due to pathogens during the last one decade clearly shows that they can be equally at risks as the meat products are in contracting infection from the field. Too much attention to animal farms, abattoirs and poultry farms by the safety monitoring authorities probably ignored the potential for microbial contamination of plant foods from the growing areas through water, soil and manure. It was rather startling to note that almost half the food poisoning episodes in the world originated in plant foods like leafy greens, cantaloupes, mangoes, strawberries, peanuts, walnuts and others causing significant mortality among consumers. This situation probably calls for a more vigorous study to get a better insight into this reality. 

The cultivation practices and the farm land locations do contribute to the vulnerability of agricultural crops to microbiological contamination. Inputs like water, and manure can be critical in maintaining freedom from pathogens while proximity to animal and poultry farms and sewage processing facilities makes the plant crops doubly susceptible to cross contamination with high probability. If the cultivated area is near to forest areas visits by animals during nights cannot be entirely avoided and their fecal droppings are a strong source of microbes of different types with varying pathogenicity. There is also the possibility of pathogens getting on vegetables and fruits in processing facilities where they are cleaned up and packed for distribution to super markets. Storage and distribution facilities if not properly sanitized frequently can cause cross contamination. In the absence of reliable traceability regime it may e next to impossible to pin point the source of contamination.

A revealing fact is that in most contamination episodes with fruits and vegetables the pathogens are found mostly on the surface though no studies have ever been carried out to find out whether these bacteria are present inside also and if so how deep they are inside. It will be a terrible tragedy if contaminating organisms find their way inside the plant and the crops through the root system. After all the fields where plants are grown can have billions of microorganisms belonging to hundreds of different species, most of them benign but some highly pathogenic. It has  to be remembered that the deadly E.coli O157:H7 strain which caused many poisoning episodes during the last few years originated in the field where soil was contaminated with fecal droppings of animals like deer and pigs. In spite of so many studies taken up to find whether disease causing bugs like bacteria and viruses can really be absorbed by the roots to be ending up in edible parts of the plant, no evidence had surfaced which support the theory that they might enter the plant under right circumstances.

It is true many bacteria show an ability to migrate towards the roots of many plants but they stay just there without migrating into the internal parts of the plant. Yet they do posses the potential to spread to other external parts of the plant during harvesting and cleaning. This is the reason why new food safety laws being enacted in some countries stipulate that for ensuring safety of fresh produce it is imperative that pathogen free water is used for irrigation and washing, the equipment and machinery deployed do not harbor pathogens and the farm workers are provided with clean water for washing their hands clean during all farm operations. In fact growing of organic foods is an ideal model for main stream agriculture community to emulate for keeping their produce free from disease causing microorganisms. Probably world is moving slowly to a stage where fresh produce which are consumed without cooking are grown only under strictest environmental and field conditions that will not give any scope for contamination with bacteria like Listeria, Salmonella and E.coli O157:H7.

When food borne diseases are discussed there is a unique creature that causes more than 60% of food poisoning episodes which has not received much attention at the hands of food microbiologists and this is the ubiquitous Noroviruses which can contaminate foods during handling stage. It was recently discovered that these viruses have the uncanny ability to contaminate surface areas of fruits and vegetables and normal washing may not be that much effective in getting rid of them easily. This is all the more true with leafy greens like spinach and lettuce which have many openings on the leaf surface called stomata for regulating transmission of gases and water vapor. The guard cells which are located on the surface of the cells can be penetrated easily by viruses,  provide a safe place for the viruses especially when there is a film of water on the surface. Standard washing procedures are not effective in gorging them out and if the contamination density is high, such consignments can cause poisoning episodes when sold in the retail market. Probably in such cases prevention is better than cure and there is no alternative but to guard against contamination at every stage of handling them to exclude incidence of Norovirus contamination.                    

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