Close association of verotoxin (Shiga-like toxin) production with enterohemolysin production in strains of Escherichia coli

Sixty-four verotoxin-producing (VT+) Escherichia coli strains were analyzed for VT1- and VT2-specific DNA sequences and for production of hemolysin. Strains of human origin were of the following serotypes: O157:H7 or H-, O111:H8 or H-, O26:H11, O114:H4, and rough:H7. Strains of serotypes O157:H7, O113:H21, O116:H21, and rough:H- were from cattle, while those of serotype O139:K12:H1 were from pigs. All 64 isolates carried either VT1 or VT2 or both genes. Sixty of the strains (93.8%) were hemolytic (Hly+). The three O139:K12:H1 strains examined produced alpha-hemolysin, as shown by their reaction with the alpha-hemolysin-specific monoclonal antibody h2A and by DNA hybridization with an alpha-hly gene probe. The remaining 57 Hly+ strains (95%) produced a different type of hemolysin (enterohemolysin), which is genetically and serologically unrelated to alpha-hemolysin. The two types of hemolysin are further distinguished by the appearance of the lysis zone on blood agar and by the time interval for the detection of hemolysis. In contrast to alpha-hemolysin, enterohemolysin can be detected only on blood plates containing washed erythrocytes. The frequent association of enterohemolysin with verotoxin production (89%) makes it useful as an epidemiological marker for rapid and simple detection of potential VT+ E. coli.