There is a fascinating artilce posted on Nature News about the link between the use of antibiotics and the emergence of so-termed 'super-strains' of bacteria, like the recent E. coli strain (O104:H4) in the news.
According to the article, the bacterium in this outbreak, currently recognised as strain O104:H4, makes Shiga toxin, which is responsible for the severe diarrhoea and kidney damage in patients whose E. coli infections develop into haemolytic uremic syndrome (HUS). The genes for the Shiga toxin are not actually bacterial genes, but phage genes being expressed by infected bacteria. So when an E. coli bacterium gets infected with a Shiga-toxin-producing phage, it becomes pathogenic to humans. Our use of antibiotics may be helping those viral genes to spread. If bacteria are exposed to some types of antibiotics they undergo what is called the SOS response, which induces the phage to start replicating. Active replication of the phage causes the bacterial cells to burst open, which releases the phage. It also releases the toxin, which is why antibiotics are not usually used to treat E. coli infection.
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