Shiga toxin-producing Escherichia coli (STEC)

Abstract

Shiga toxin-producing Escherichia coli (STEC) are important enteric pathogens worldwide, causing diarrhea with or without blood visibly present and hemolytic uremic syndrome. STEC are unique among diarrheogenic E coli in producing Shiga toxin type 1 and type 2, the virulence factors responsible for bloody diarrhea and hemolytic uremic syndrome. Cattle and other ruminants are the natural reservoir of STEC as their normal intestinal flora. Humans become infected by consumption of foods contaminated with cattle feces. Early diagnosis of STEC infection is important because of the contraindication for treating STEC using antimicrobial agents, and the intense supportive care needed if renal failure occurs.

Fig. 1

Cattle and other ruminants are natural reservoirs of STEC.

Fig. 2

Shiga toxin (Verotoxin) effect on Vero cell monolayers. (A) Medium control, 1 day, cells in continuous monolayer. With STEC filtrate, (B) 1 day, (C ) 2 days, (D) 5 days; monolayer being destroyed. Phase-contrast microscopy. Magnification ×237.

Fig. 3

Antigenic structure of Enterobacteriaceae.

Fig. 4

Circular representation of the E coli O157 chromosome. The outermost circle indicates locations on the 5.5-MB genome. The second and third circles show in red the predicted genes in O157 that differ from those of a nonpathogenic laboratory strain of E coli. The fourth circle indicates in black the locations of the integrated temperate bacteriophage genomes encoding Stx1 and Stx2 in the O157 chromosome.

Fig. 5

Shiga toxin lateral-flow immunoassay device for testing broth and agar cultures. This device distinguishes Stx1 from Stx2.

Fig. 6

Interactive map showing location in United Kingdom and Wales of two STEC O157:H7 outbreaks, July, 2009.

Fig. 7

Normal intestinal mucosa. (A) Luminal surface of the normal small intestine, with enterocytes lining the villi and intestinal crypts. (B) Normal colon histology showing colonic crypts and a flat mucosal surface lined with enterocytes. The enterocytes are the target of STEC Shiga toxins. H&E staining. Magnification ×70 approximately.

Fig. 8

Ribbon diagram of Stx2 from E coli O157:H7. Shiga toxin is a class AB5 toxin. The monomeric A polypeptide is red. The five B polypeptides are orange, cyan, green, yellow, and blue. Binding of the pentameric B portion of the toxin to the cell surface allows entry of the A subunit into the cell, where it functions enzymatically to stop protein synthesis and kill enterocytes and other cells to which the Shiga toxin binds.

Fig. 9

Fibrin stain showing platelet-fibrin thrombi (dark areas) in the glomerular capillaries. Glomerular injury is characteristic of microangiopathic disorders, such as hemolytic uremic syndrome (HUS). Fibrin stain. Magnification ×240 approximately.