Tuesday, January 24, 2012

Want to know more about the origin of Shigatoxin-producing E. coli?

 Bill Marler is a very rare individual: he is a lawyer with an ability to grasp the principles of microbiological food safety and to write about them in a way that is accessible to the general public.  Bill has been closely involved in food borne illness litigation since 1993, when he obtained a $15.6 million settlement for Brianne Kiner, a nine year old girl who suffered HUS and ultimately kidney, liver and pancreas failure after eating Jack-in-the-Box hamburger.  He has become a fiercely active food safety campaigner.

Recently, Bill conducted a literature review on the origins of Shigatoxin-producing Escherichia coli  and has published the first two parts on his food safety blog.  These publications are well worth reading - they are not written in highly technical language, but the reference list allows those readers sufficiently interested and capable to follow up his sources and read the original material.

Links to the first two parts are shown below:

There is just one problem with this review; Bill has taken away my option to set such a study of literature as an assignment for my postgraduate students in my course "Frontiers of Food Microbiology".  The students will still be expected to read and discuss the material, but I can't use their reviews for assessment purposes.  Thanks Bill!

Saturday, January 21, 2012

Who ya gonna call - Ghost Busters?

The title is perhaps a bit over the top for a food safety blog, but there is a link!  Last week I spent a lot of time in my car and listened to many old tapes, including the theme song from Ghost Busters.  According to my stats over the past week, a popular search phrase has been "Polysaccharide slime". It seemed propitious to write a short article on bacterial slime.

Bacterial biofilms produce large amounts of polysaccharide.  Polysaccharides are chains of simple sugar molecules.  Some polysaccharides are tough and fibrous but others can be slimy.

Bacteria growing in suspension, the so-called planktonic phase, generally don't produce large amounts of slime.  However, for most bacteria, the normal mode of growth is as a biofilm - an aggregation of cells attached to and growing at a solid-liquid interface.  It has been estimated that when the cells settle on the surface, up to 30% of the genome is switched on or off;  the biofilm mode of growth is very different from the planktonic mode.

Among the changes is the production of large amounts of extracellular polymeric substance (EPS) much of which is polysaccharide.  The EPS glues the cells to the surface and protects them from materials such as detergents, sanitisers and antibiotics.  It also confers some advantages, such as immobilising extracellular enzymes.

In the food industry, we see EPS helping biofilms to remain in processing plant during cleaning, or bacteria spoiling foods such as meats by producing surface slime.  However, not all slime is involved in food spoilage - dextran, produced by Leuconostoc mesenteroides  and Streptococcus mutans and some other bacteria has laboratory and medical applications and may be used in construction of biosensors.

Monday, January 9, 2012

Moulds and mycotoxins

Pepin Heights Orchards and Minnesota Department of Agriculture have issued advice to consumers not to drink certain batches of Honeycrisp Apple Cider because of the presence of patulin at levels slightly above the 50 microgram per litre maximum level recommended by the World health Organisation. See: http://www.prweb.com/releases/2012/1/prweb9085429.htm

Patulin is one of a host of compounds produced by moulds. These compounds are collectively referred to as "Mycotoxins".

We don't hear a lot about mycotoxins in the popular press - outbreaks of food borne illness are usually caused by Salmonella, Listeria, Campylobacter, or Escherichia coli, with several other bit players.

In fact, many fungi produce mycotoxins. One of my older textbooks devotes 66 pages of its 750 to these chemicals, some of which are very complex molecules. There is considerable discussion as to why moulds produce them, but they are probably just by-products of metabolism, though it has been suggested that in some cases, excretion of these "secondary metabolites" may confer some selective advantage, perhaps by inhibiting competitors in the soil.

Some of these chemicals can be very toxic - I well remember 1960 as the year when it was not possible to buy a turkey for Christmas in the UK, because thousands of young turkeys on poulry farms had died of the mysterious "Turkey X Disease". This was later shown to be caused by Aflatoxin present in peanut meal from Brazil as a result of growth of Aspergillus flavus mould. Intoxication of both humans and animals may be acute, but long term exposure may lead to cancer development.

Patulin in not regarded as particularly toxic to humans, but its presence in apple products is an indication of the quality of the apples used to make the products. There is some inconclusive evidence that patulin is genotoxic, i.e. it can damage the cell's genetic material. Pepin Heights has therefore been very responsible in their actions.

In America, fresh pressed apple juice is called Cider. In Europe, Cider, or Cidre is fermented apple juice. Patulin does not survive the fermentation process, so fermented cider is not likely to be contaminated with patulin.

Odd spot: a numbeer of mycotoxins are beneficial to humans, as they are in fact antibiotics - penicillin is just one example. Many drugs have also been made from mycotoxins.
St Anthony's Fire - ergot poisoning, has been known since about 600 BCE, but the pure ergotamine can be used to treat migraine.

For a much more complete, but readable, description of mycotoxins, go to: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC164220/