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.



2 comments:

Anonymous said...

Would xanthan also be an example of beneficial EPS?

John Brooks said...

Yes indeed. Xanthan is derived from Xanthomonas species and is used extensively as a gum for stabilisation and thickening in food processing. You can read more about it at:
http://en.wikipedia.org/wiki/Xanthan_gum

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