Fruit and vegetables
What is causing the sticky film on that melon? Or the dull varnish on that apple? Might it be a layer of gooey goodness akin to that of a glazed donut? Not likely, but it could be a biofilm.
As an excellent source of beta carotene and vitamins A and C, cantaloupe melons are a popular choice for a nutritious, mildly sweet snack. But on at least six different occasions, cantaloupe melons contaminated with Salmonella enterica have been the source of salmonellosis outbreaks. Although most victims recover without treatment, the symptoms of salmonellosis—abdominal cramping, diarrhoea, and fever—last 4–7 days. Cattle and poultry are often infected with S. enterica, but some domestic animals such as cats and hamsters can also be sources of infection. Regardless of the source of transmission, once S.enterica attaches itself to cantaloupe melons it will begin to form biofilms within 24 hr during storage at 10° C and 20° C. Sanitisers are ineffective at removing or inactivating S. enterica biofilms on cantaloupes, especially if it has been present on the rind for more than 24 hr.
The adage “an apple a day keeps the doctor away” may not always be true. Even though there have been no foodborne illness outbreaks associated with fresh apples, there have been seven instances of either apple juice or apple cider contaminated with the bacterium Escherichia coli. This bacterium normally lives in the intestines of ruminant animals such as cattle, goats, and sheep. The symptoms of E. coli infections in people are usually mild but frequently involve severe stomach cramps, diarrhoea and vomiting; some victims suffer more severe—and even life-threatening—complications. When E. coli is present on the surface of apples it compromises the safety of fresh juice and fresh-cut fruit produced. Research indicates that washing apples with water and detergents or sanitising agents measurably reduces the amount of E. coli present. However, industrialised washing techniques such as flatbed brush washers may not be so effective. The reason for the difference could be attributed to bacteria attaching to inaccessible regions such as the stem, core, and calyx of apples and to the formation of E. coli biofilms on apple surfaces.
In the never-ending quest to lose weight, many individuals rely on the consumption of fresh salads as part of their diet. Pre-packaged salads and minimally-processed leafy greens may be important for a reduced calorie lifestyle, but as of late, they have also been the most frequent source of foodborne illness. In the USA, the Food and Drug Administration has linked 18 outbreaks of E. coli to lettuce and one outbreak to spinach. Basil, cabbage, coriander, green onions and parsley are also responsible for outbreaks of foodborne illness. Hundreds of illnesses and even some deaths have resulted from these outbreaks. Commercial operations typically use triple-wash treatments and disinfectants to clean leafy vegetables. Nonetheless, conventional sanitation processes for cleaning leafy products do not reduce pathogen levels sufficiently to ensure microbiological safety. The cause for this is because pathogens in biofilms are very strongly attached. For example, E. coli was able to colonise and form biofilms on lettuce leaves submerged in water and incubated for one week at 4° C. To reduce the presence of biofilms on leafy products, more thorough washing and sanitation strategies are necessary to overcome the substantive cohesive properties of biofilms, which quorum sensing facilitates.
Further reading on biofilms and fruit and vegetables
This summary was taken from Biofilms: A Threat to Food Safety. Food technology magazine. Feb 1, 2009. Please see the link for the rest of the article and the references.
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