Perspective: The Problem of Non-O157:H7 Shiga Toxin (Verocytotoxin)--Producing Escherichia coli

Abstract

Escherichia coli OI57:H7 causes diarrhea, hemorrhagic colitis, and the hemolytic uremic syndrome (HUS) [1,2].The cardinal virulence trait of E. coli OI57:H7 is the production of Shiga toxins (Stx, also termed Verocytotoxins) [3,4].Unlike most coliforms in human feces, E. coli 0157:H7 does not ferment sorbitol after overnight incubation [5].Therefore, it is easily and economically detected by laboratories using sorbitol-MacConkey (s-Mac) agar screening to identify sorbitol-nonfermenting candidate E. coli 0157 :H7 [6,7].Such colonies are then tested for the presence of the 0157 antigen, which, if detected, presumptively identifies Stx-producing E. coli (STEC) 0157:H7.In contrast, it is not known which of the many STEC belonging to serotypes other than OI57:H7 (non-OI57:H7 STEC) are pathogens; with rare exceptions [8,9], such organisms ferment sorbitol and would be overlooked on an s-Mac agar plate.The same difficulty applies to the detection of sorbitol-fermenting Stx-producing E. coli 0157:NM, a pathogen in Germany [10].In this issue, Ludwig et a1.[11], report that 6 of 8 HUS patients from whom non-0157:H7 STEC were isolated produced antibodies to the O-specific lipopolysaccharide of the putatively causative strains.Ludwig et a1.also determined that patients infected with E. coli expressing 0 antigens 26, 55, and 111 did not make antibodies to the 0157 lipopolysaccharide.Humans infected with E. coli 0157:H7 respond briskly with antibodies to the 0157 antigen [12][13][14][15][16], so absence of anti-0157 antibodies probably exonerates E. coli OI57:H7 as the pathogen that precipitated the HUS.This is an important point, because children from whom such non-0157:H7 STEC have been isolated sometimes produce convalescent antibodies to the 0157 lipopolysaccharide [12][13][14], suggesting that E. coli 0157:H7 was missed in the stool culture.Furthermore, simultaneous enteric infections with E. coli 0157:H7 and non-0157:H7 STEC have been reported [17,18].This work, therefore, supports strongly the hypothesis that Stx production by a variety of E. coli is a crucial pathogenic factor, as first postu-

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Affiliated Institutions

• Children's Hospital & Medical Center US
• Memorial Hospital of Rhode Island US
• Brown University US
• University of Washington US

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