General Laboratory Information on E. coli Serotypes
The O-specific or cell wall antigen of E. coli is a polymer of repeating oligosaccharide units of three or four monosaccharides. Within certain E. coli these polymers vary with different isolates, which allows for serologic subgrouping of the genera.
The flagellar, or H antigen's are proteins. The antigenic variation of the various flagella types is due to differences in amino acid sequences. Serological typing of flagella antigens helps form the basis of antigen types of E. coli.
Approximately 85% of O157 isolates from humans received by CDC are serotype O157:H7, 12% are nonmotile, and 3% are H types other than H7. E. coli O157:H7:NM (nonmotile) strains frequently produce Shiga-toxin and are otherwise very similar to O157:H7, but no O157 strain from human illness with an H type other than H7 has been found to produce Shiga toxin. At least 100 serotypes of non-O157 shiga-toxin positive E. coli have been isolated from persons with diarrhea or HUS.
Shigella and E. coli are identical by DNA-DNA hybridization analysis, and with the exception of Shigella boydii 13, would be considered the same species. Phenotypic characteristics rather than genotypic characteristics (biochemical and serologic reactions) differentiate them in most clinical diagnostic laboratories.
Understanding foodborne outbreaks through DNA fingerprinting of E. coli O157:H7, and other bacteria through PulseNet.
PulseNet is a national network of public health laboratories that performs DNA "fingerprinting" on bacteria that may be foodborne. The network permits rapid comparison of these "fingerprint" patterns through an electronic database at the Centers for Disease Control and Prevention (CDC). The DNA "fingerprinting" method is called pulsed-field gel electrophoresis (PFGE).
Similar PFGE patterns suggest that the bacteria isolated from ill persons come from a common source, for example, a widely distributed contaminated food product. Strains isolated from food products by regulatory agencies can also be compared with those isolated from ill persons. Identifying these connections can help to detect outbreaks and remove contaminated foods from the marketplace.
ref.: Man. Clin. Micro, 7th ed., 1999., and Zinsser Microbiology
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