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Cross-Reactions Between E. coli 0 Antigens and Antigens Outside the Enterobacteriaceae Group .669

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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: 0157:H7 or H-, 0111:H8 or H-, 026:H1l, 0114:H4, and rough:H7. Strains of serotypes 0157:H7, 0113:H21, 0116:H21, and rough:H-were from cattle, while those of serotype 0139:K12:Hl were from pigs. Ail 64 isolates carried either VT1 or VT2 or both genes. Sixty of the strains (93.8%) were hemolytic (Hly+). The three 0139:K12:H1 strains examined produced a-hemolysin, as shown by their reaction with the a-hemolysinspecific monoclonal antibody h2A and by DNA hybridization with an a-hly gene probe. The remaining 57 Hly+ strains (95%) produced a different type of hemolysin (enterohemolysin), which is genetically and serologically unrelated to a-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 a-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.

The genetic relationships among 1,300 isolates of Escherichia coli representing 16 serotypes associated with enteric disease, including O157:H7 strains recovered from patients with hemorrhagic colitis and hemolytic uremic syndrome and O26:H11, O55:H6, O55:H7, O111:H2, and O128:H2 strains, many of which were isolated originally from infants with diarrhea, were estimated from allelic variation among 20 enzyme-encoding genes detected by multilocus enzyme electrophoresis. Multiple electrophoretic types were observed among isolates of each serotype, with isolates of the same O serogroup differing on average at 28% of the enzyme loci. Comparisons of the multilocus enzyme profiles revealed that 72% of the isolates belong to 15 major electrophoretic types, each of which corresponds to a bacterial clone with a wide geographic distribution. Genetically, the O157:H7 clone is most closely related to a clone of O55:H7 strains that has long been associated with worldwide outbreaks of infantile diarrhea. We propose that the new pathogen emerged when an O55:H7-like progenitor, already possessing a mechanism for adherence to intestinal cells, acquired secondary virulence factors (Shiga-like cytotoxins and plasmid-encoded adhesins) via horizontal transfer and recombination.

When Theodor Escherich (1885a, b) first describedEscherichia colihe looked on it as a saprophytic organism. Soon several investigators found that colibacteria could be isolated from intestinal infections and from many infections outside the intestine, like urinary tract infections (UTI), cholecystitis, wound infections, meningitis, septicaemia, pulmonary infections, and many more. Uhlenhuth (1897) showed that coli strains from pathological processes were more pathogenic in animal experiments than strains isolated from the normal intestine. Smith (1927), who examined strains from white scours in calves, showed that spontaneous acapsular mutants could be obtained from certain colibacteria, and that such mutants were less virulent when injected intra-peritoneally into guinea-pigs.

Sixty-three Escherichia coli strains isolated from neonatal sepsis or meningitis were studied and compared with previous data on fecal or urinary pyelonephritis-associated isolates from children. Characteristics significantly associated with neonatal infection were capsular type Kl (54%), 0 group 18 (27%), rough-type lipopolysaccharide together with Kl capsule (19%), and S fimbriae (29%). Within the neonatal infection group, the Kl capsule and rough lipopolysaccharide were most common among the youngest infants (O to 21 days old) and in meningitis. Hemolysin production, P fimbriae, and X adhesins (adhesins not identifiable as type 1, P, or S) were significantly more common in the two materials from infections as compared with the fecal isolates. One large clone of 11 strains (018:K1:H7, with both type 1 and S fimbriae) and three smaller ones