Epidemiology of Argentinean STEC

RIVAS M; CHINEN I; MILIWEBSKY E; GALLI L; REPETTO HA; MASANA MO

Bacterial Population Genetics: A Tribute to Thomas S. Whittam

American Society for Microbiology Press

Lugar: Washington; Año: 2011; p. 109 - 132

Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogenwhich can cause nonbloody diarrhea, hemorrhagic colitis, and hemolytic uremicsyndrome (HUS) (14). HUS, a life-threatening complication that occurs in 5-10% of patients, is characterized by hemolytic anemia, thrombocytopenia, and renal failure. No specific treatment exists for post-enteric HUS and the mortality rate among children with this type of HUS is 3-5%. The dominant STEC serotype is O157:H7, which was identified as a human pathogen in 1982, and since then has been responsible for numerous outbreaks and sporadic cases in different parts of the world. However, there have been increasing reports of non-O157 strains associated with gastrointestinal infections. These serotypes differ in their frequency and severity of human disease, suggesting differences in their virulence characteristics. The production of Shiga toxin 1, Shiga toxin 2, and/or their variants (Stx1c, Stx2c, Stx2-O118, Stx2-OX3a, Stx2dactivatable, and Stx2f) is the primary virulence trait responsible for human disease. Another virulence-associated factor of most STEC isolates is a 94-kDa outer membrane protein, called intimin, which is encoded by the eae gene on a ca. 34-kb chromosomal pathogenicity island termed the locus of enterocyte effacement (LEE). This locus is associated with intimate adherence to epithelial cells, initiation of host signal transduction pathways, and formation of attaching-and-effacing intestinal lesions. However, the presence of this island is not essential for pathogenesis, as a wide number of LEE-negative STEC strains are capable of causing human disease. The products of several genes have been suggested to play a role in virulence. These products include adhesins, toxins, proteases, iron acquisition systems, LPS, and flagellin. In addition, most STEC strains produce an enterohemolysin (EHEC-Hly), encoded by a large plasmid-borne (90-kb) gene known as ehxA, that has been associated with severe clinical disease in humans. Cattle and other ruminants have been implicated as the main reservoir of O157:H7 and non-O157 strains. STEC infections are transmitted to humans through contaminated food, water, and direct contact with infected persons or animals.