Epidemiology, pathogenesis and diagnosis of human diseases caused by enterohaemorhagic Escherichia coli O157 : H7 (EHEC).

Enterohaemorrhagic Escherichia coli O157:H7 (EHEC) was recognised as a huma n pathogen following outbreaks of haemorrhagic colitis (HC) in the USA, 198 2. Since then EHEC became an emerging food-related pathogen causing a wide variety of diseases in human including mild to bloody diarrhoea, haemorrhag ic colitis (HC) that can lead to the life threatening haemolytic uremic syn drome (HUS). EHEC infection is a severe public health problem in developed countries. In 1996, there was an outbreak involving more than 6000 people i n Japan. In the United States, the number of EHEC infections could be as hi gh as 20000 per a year, of which about 250 are deadly. The source of infect ion is mostly eating undercooked ground beef. In Hungary, there have only b een sporadic cases detected so far. With several virulence factors involved in its pathogenesis, EHEC is a classic pathogenic model organism. All isol ates have one or two bacteriophage encoded toxins, called Shiga toxin (Stx) , a serotype specific virulence plasmid of cc. 60 MDa (pO157) and a pathoge necity island (pai). pO157 promotes the EHEC adherence both in vivo and in vitro, but so far there is no cloned pO157-specific EHEC adhesin. pO157 enc odes Katalase peroxidase (KatP), Serine protease (EspP), EHEC-haemolysin (e nterohaemolysin) and a type II secretion pathway operon. EHEC-pai is a 43.3 kb length extraneous DNA that contains all the genes necessary for causing attaching effacing lesions. Diagnosis is mostly based on the detection of Stx through its cytotoxic effect on Vero cells, with the help of Stx-antibo dies, by hybridisation using Stx specific DNA probes or by DNA amplificatio n (PCR). The antibiotic therapy of EHEC infections is not without risk and further studies are needed to elucidate its benefits. There are encouraging results of using a Stx-receptor analogue to develop drugs or vaccines.