Photo: US NIH
Did you know ... ? – E. coli
Escherichia coli, more commonly known as E. coli, is the most common bacterium living in the gut of all warm-blooded animals. The species name coli refers to its occupation of the colon.
It is a normally harmless rod-shaped bacterium that takes advantage of the conditions in the gut and benefits its host by excreting vitamin K and by physically excluding pathogenic bacteria.
Because E. coli can survive for a while outside the body (benefiting it by giving it time to find a new host), and because it is easily grown in the laboratory, it makes an excellent indicator of water contamination. Although it is normally harmless, coming from the gut in faeces, it is accompanied by pathogenic bacteria that can be hard to grow in the lab, so if you find E. coli, it means that you’ve probably also found pathogens.
Nevertheless, some strains of E. coli are pathogens themselves, notably O157:H7, which can cause diarrhoea and sometimes death, as happened a few years ago from salamis made in Adelaide.
Because its complete genetic sequence has been decoded, and because the bacterium is easily grown in the lab, E. coli makes an ideal organism for the production of useful compounds. Through gene transfer, strains of E. coli have been created that produce human insulin. The insulin is chemically and physically identical to natural human insulin, and so is tolerated far better than insulin extracted from pigs.
Because E. coli is a world standard indicator of water contamination, its detection forms part of SESL’s standard suite of water quality tests. Test reports refer to either E. coli or “coliform” bacteria. “Coliform” simply refers to bacteria like E. coli. Results are expressed as colony-forming units per litre, or cfu/L. One cfu/L refers to one live bacterium per litre of water that grows into one bacterial colony on nutrient agar in a Petri dish. Anything less than 10 cfu/L is considered acceptable for drinking water.
Further reading
Wikipedia: http://en.wikipedia.org/wiki/Escherichia_coli
Recombinant DNA Technology in the Synthesis of Human Insulin: http://www.littletree.com.au/dna.htm
Australian Drinking Water Guidelines: http://www.nhmrc.gov.au/publications/synopses/eh19syn.htm
Sydney Water quarterly drinking water quality report: http://www.sydneywater.com.au/WaterQuality/QuarterlyDrinkingWaterQualityReport/