Detection of Virulence Determinants in Enteric Escherichia coli Using Nucleic Acid Probes and Polymerase Chain Reaction

Summary

As certain strains of Escherichia coli are a major cause of diarrhea both in man and animals, diagnosis of the specific etiological agents must be carried out beyond the species level. Several different pathogroups have been identified and for some of them, also the specific virulence determinants. Traditional microbiological assays have to a certain degree been supplemented or replaced with nucleic acid-based methods, like hybridization assays using cloned fragments or oligonucleotides as probes. Recently, the polymerase chain reaction (PCR) has been shown to be a suitable tool for differentiation between E. coli strains belonging to the normal enteric flora, and those carrying specific virulence determinants. Probe assays have been established in some diagnostic laboratories and found to be reliable for detection of the different enterotoxins of both the heat-stable-(ST) and the heat-labile-(LT) -families, and the shiga-like cytotoxins (SLTs). Different setups of the PCR principle have also been used to identify and characterize such genes. Genes encoding some of the important adhesion fimbria, characterizing such toxin-producing strains, have been targets for some assays. Several of the genes involved in the invasion process of the enteroinvasive E. coli are routinely identified using probe assays, avoiding the use of cell-cultures or laboratory animals. The enteropathogenic E. coli strains have for years been defined as a serological cluster, and different probes for both plasmidial and chromosomal genes have now confirmed the presence of common virulence properties. Probes and PCR are becoming very important diagnostic tools in identification and characterization of virulence- or virulence-associated genes in E. coli.