The presence of the virulence markers K1 capsule, serum resistance, aerobactin, S and P/PR fimbriae were examined in a total of 395 E. coli strains from different extraintestinal infections and in 81 faecal isolates of healthy volunteers using specific DNA probes and classical phenotypic methods. All markers were more frequently detected when genotypic assays were applied. The simultaneous occurrence of 3–4 virulence determinants was typical for isolates derived from patients with septicaemia or meningitis. Isolates from blood cultures and cerebrospinal fluid were expressing the virulence phenotypes to a greater extent than isolates from urine or faeces. The use of colony hybridization with specific oligonucleotide and polynucleotide probes for the detection of virulence determinants has been proven to be more specific and reliable than phenotypic approaches.

The presence of S and F1C/S-related fimbrial determinants was determined in 462 E. coli strains obtained from different extraintestinal infections and in 162 control isolates of E. coli by using two different DNA probes: an oligonucleotide probe consisting of three oligonucleotides that bind specifically to the S adhesin gene and a polynucleotide probe which is not able to distinguish between S, F1C, and S-related sequences. The expression of S and F1C phenotypes was tested by dot enzyme immunoassay with the corresponding monoclonal antibodies. S fimbriae genotypes were observed more frequently in septic (25%) and urinary (12%) isolates of E. coli than in faecal and water isolates (1%) and often occurred together with O2, O6, O18 and O83 antigens. F1C/S-related fimbrial DNA was detected with a higher frequency in UTI isolates (26%) than in septic (16%) and faecal (10%) isolates and was most frequently associated with O4, O6, and O75 serotypes. Since the production of S and F1C fimbriae was comparatively rare in all clinical and control isolates of E. coli, DNA hybridization assays which allow the sensitive and specific detection of fimbrial determinants even in the absence of their expression are preferable to phenotypic assays.

The presence of the virulence markers K1 capsule, serum resistance, aerobactin, S and P/PR fimbriae were examined in a total of 395 E. coli strains from different extraintestinal infections and in 81 faecal isolates of healthy volunteers using specific DNA probes and classical phenotypic methods. All markers were more frequently detected when genotypic assays were applied. The simultaneous occurrence of 3-4 virulence determinants was typical for isolates derived from patients with septicaemia or meningitis. Isolates from blood cultures and cerebrospinal fluid were expressing the virulence phenotypes to a greater extent than isolates from urine or faeces. The use of colony hybridization with specific oligonucleotide and polynucleotide probes for the detection of virulence determinants has been proven to be more specific and reliable than phenotypic approaches.