Shiga Toxin–producing Escherichia coli Serotype O78:H^– in Family, Finland, 2009

Taru Lienemann, Eeva Salo, Ruska Rimhanen-Finne, Kai Rönnholm, Mari Taimisto, Jari J. Hirvonen, Eveliina Tarkka, Markku Kuusi, and Anja Siitonen

Author affiliations: National Institute for Health and Welfare, Helsinki, Finland (T. Lienemann, R. Rimhanen-Finne, M. Kuusi, A. Siitonen); University of Helsinki, Helsinki (E. Salo, K. Rönnholm, E. Tarkka); Vaasa Central Hospital, Vaasa, Finland (M. Taimisto, J.J. Hirvonen)

Abstract

Shiga toxin–producing Escherichia coli (STEC) is a pathogen that causes gastroenteritis and bloody diarrhea but can lead to severe disease, such as hemolytic uremic syndrome (HUS). STEC serotype O78:H^– is rare among humans, and infections are often asymptomatic. We detected a sorbitol-fermenting STEC O78:H^–:stx_1c:hlyA in blood and fecal samples of a 2-week-old boy who had bacteremia and HUS and in fecal samples of his asymptomatic family members. The phenotypic and genotypic characteristics and the virulence properties of this invasive STEC were investigated. Our findings demonstrate that contrary to earlier suggestions, STEC under certain conditions can invade the human bloodstream. Moreover, this study highlights the need to implement appropriate diagnostic methods for identifying the whole spectrum of STEC strains associated with HUS.

Diarrheagenic Escherichia coli strains, particularly Shiga toxin–producing E. coli (STEC), are foodborne and waterborne pathogens that cause a wide spectrum of symptoms, ranging from mild gastroenteritis to severe diseases such as hemorrhagic colitis, thrombotic thrombocytopenic purpura, and hemolytic uremic syndrome (HUS) (1). STEC has been characterized as a moderately invasive enteric pathogen because it is unable to invade the host cell cytoplasm but secretes phage-encoded Shiga toxin (Stx) that activates the signal pathway, leading to cell death and disease. Several reports have demonstrated the ability of STEC strains to invade epithelial cells in vitro, although in small numbers (2,3), but no reports of invasion in vivo have been published.
Stx plays a major role in intense inflammatory response and may explain the ability of STEC strains to cause HUS. The stx genes are located in a bacteriophage integrated into the bacterial genome, and the production of Stx is linked with the replication cycle of the phage (4). Stx has 2 major subfamilies: Stx1 and Stx2. Those producing variants Stx2a, Stx2c, and Stx2d_activable have been associated with more severe illness and HUS, whereas the other variants were often associated with uncomplicated diarrhea and asymptomatic infections (5). The colonization mechanism for the cell invasion is not yet fully understood, but the bacterium is known to attach firmly to the epithelial cells through an outer membrane protein called intimin. This protein is encoded by the gene eae on a pathogenicity island called the locus of enterocyte effacement, and the bacterial fimbriae are presumed to be involved in the process (6).
HUS is characterized by acute onset of microangiopathic hemolytic anemia, renal injury, and low platelet count (7). It is primarily a disease of infancy and early childhood because infants and young children are more vulnerable than adults, even for low Stx concentrations; however, humans of all ages can be affected. The reported STEC infections, especially with a linkage to HUS, have been frequently caused by strains of the sorbitol-negative serotype O157:H7 (8). However, some sorbitol-positive strains of non–O157 STEC serotypes also cause a similar spectrum of signs and symptoms (9).
Infections with STEC of serotype O78:H^– are rare among humans and often linked with asymptomatic infections. We describe a family cluster caused by STEC serotype O78:H^– associated with neonatal bacteremia and diarrheal (D+) HUS.