Sorbitol-Fermenting Enterohemorrhagic Escherichia coli O157:H–

A relative of enterohemorrhagic Escherichia coli (EHEC) O157:H7, namely, sorbitol-fermenting (SF) E. coli O157:H- (nonmotile), is an important and fascinating human pathogen. The author highlights that researchers were quite motivated to find the infecting pathogen, because the PCR with primers MK1/MK2 from the enrichment culture was positive, the sorbitol MacConkey (SMAC) agar results not withstanding. Therefore, these researchers performed a colony blot hybridization test. The colonies identified with this procedure agglutinated in anti-O157 serum. Because of their ability to ferment sorbitol after overnight incubation, SF EHEC O157:H- strains cannot be distinguished from the physiological intestinal microflora using SMAC agar. This medium remains the most commonly used, rapid, and appropriate way to isolate EHEC O157:H7. At the beginning of the 1990s, researchers sought to identify virulence factors of SF EHEC O157:H- and to determine whether or not these strains were only slight phenotypic variants of non-sorbitol-fermenting (NSF) EHEC O157:H7 or if they were substantially different. They formulated an evolutionary model that includes several steps in the emergence of E. coli O157:H7. EHEC O157:H7 and SF EHEC O157:H- differ in several important aspects, including their phenotypes, the epidemiology of the infection, and the risk of the progression of the infection to hemolytic uremic syndrome (HUS).