E. coli has been in the media a lot recently (Latest News), so MicrobiologyBytes thinks it’s time for:
10 things you should know about E. coli:
1. Escherichia coli (E. coli) is a normal inhabitant of the human gut. It’s been with us for millions of years and overall does us a lot of good, e.g. helping with digestion and providing vitamins we can’t make for ourselves.
2. There are many different strains of E. coli, which all look much alike. They are identified by the antigens on the surface of the cell. These include somatic (O antigens) on the surface of the cell, flagellar (H antigen) and capsular (K antigens) associated with polysaccharide capsules on some strains.
3. A few strains of E. coli are pathogenic and cause disease. Enterotoxigenic (ETEC) strains cause diarrhea but are non-invasive and do not leave the intestine. Enteropathogenic (EPEC) strains also cause diarrhea and enter epithelial cells around the intestine. Enteroinvasive (EIEC) strains cause severe diarrhea and high fever. Enterohemorrhagic (EHEC) strains such as E. coli O157:H7 cause bloody diarrhea, hemolytic-uremic syndrome and kidney failure.
4. E. coli O157:H7 infections often case to bloody diarrhea and occasionally acute kidney failure, especially in young children and elderly people.
5. Most infections are associated with eating undercooked, contaminated ground beef (e.g. burgers), drinking unpasteurized milk, swimming in or drinking contaminated water, and eating contaminated salad vegetables. Infection can also be aquired via direct contact with animal faeces, for example on farms.
6. A bit of dirt never did me any harm… E. coli O157:H7 is new. It was first recognized around 25 years ago and is now widespread, possibly due to agricultural practices.
7. Where did it come from? This strain of E. coli contains lysogenic bacteriophages which encode Shiga toxins (these strains are known as STECs: Shiga Toxin Producing Escherichia coli). E. coli O157:H7 has two stx toxins, stx1 and stx2.
8. How does it cause disease? E. coli O157:H7 is an EHEC strain which kills epithelial cells in the gut, resulting in bloody diarrhea. It also invades the urinary tract causing an ascending infection which damages the kidneys. But it gets worse. Broad spectrum fluoroquinolone antibiotics such as ciprofloxacin which are often used to treat infections cause an SOS response in E. coli cells which in turn induces the lytic cycle of the lysogenic toxin-carrying phages. This results in a thousand-fold increase in toxin expression. Treatment with some some beta-lactam antibiotics also increase stx toxin production.
9. Many people recover without antibiotics or other specific treatment in 5–10 days. There is no clinical evidence that antibiotics improve the course of disease, and some may make it much worse (see above). Haemolytic-uremic syndrome is a life-threatening condition usually treated in an intensive care unit. Blood transfusions and kidney dialysis are often required. Even with intensive care, the death rate for haemolytic uremic syndrome is 3%–5%.
10. Wash your hands thoroughly with soap and warm water after contact with animals. Wash raw vegetables such as salads well before eating. Cook meat thoroughly all the way through, especially burgers and sasuages where external contamination of meat is transferred to the inside by mincing.
11. E. coli is a Gram-negative bacterium. IT’S NOT A VIRUS! So next time a journalist talks or writes about “the E. coli virus” – do us all a favour and yell at them!