Isolation and characterisation of dog uropathogenic Proteus mirabilis strains.

Proteus mirabilis strains isolated from the urine of dogs with urinary tract infections, were characterised with respect to the production of haemolysin and fimbriae. In contrast to healthy dogs, P. mirabilis was also isolated in high numbers from the faeces of dogs suffering from recurrent urinary tract infections. Production of fimbriae was demonstrated by electron microscopy and the presence of genes for two different types of major fimbrial subunits (MR/P-like or UCA-like) was demonstrated by Southern hybridisation. These genes were absent in the Proteus vulgaris, Providentia rettgeri and Morganella morganii strains tested. All but one P. mirabilis strains were haemolytic and most strains produced fimbriae albeit in different amounts. The UCA fimbrial subunits from dog and human isolates have identical molecular weights and N-terminal sequences and are immunologically cross reactive. It was concluded that dog uropathogenic P. mirabilis strains are very similar to human uropathogenic P. mirabilis strains.

Nucleotide sequences of the major subunits of F9 and F12 fimbriae of uropathogenic Escherichia coli.

An Eco RV-Cla I fragment containing the gene encoding the F9 fimbrial subunit of the human uropathogenic Escherichia coli strain C1018 and a PstI-PstI fragment containing the F12 fimbrial subunit gene of the dog uropathogenic strain 1442 have been cloned and the nucleotide sequence of the fragments determined. The structural gene of the F9 fimbriae (FniA) codes for a protein of 165 amino acid residues with a signal peptide of 25 amino acids. The F12 fimbrial gene (FtwA) codes for a protein of 155 amino acids which is preceded by a single peptide of 21 amino acids. The amino acid sequences of the FniA and FtwA proteins deduced from the nucleotide sequence were compared with sequences of other known P-fimbrial subunit proteins. As expected, most differences between the various proteins were found in the hypervariable regions defined by van Die et al. (1987). The N-terminal sequence of the FtwA protein differs from the one published by Klemm et al. (1983). FtwA contains two deletions found in comparison to the other fimbrial subunits.

Isolation and characterisation of dog uropathogenic Escherichia coli strains and their fimbriae.

A number of Escherichia coli strains have been isolated from dogs with urinary tract infections. These strains have been characterised with respect to their O, K, H, and fimbrial antigens, colicin production, antibiotic resistance, plasmid content and their ability to haemagglutinate erythrocytes from various species. Crossed immunoelectrophoresis of fimbrial extracts, as well as the reaction of partly purified fimbriae of a number of these strains with monoclonal antibodies revealed homology or a strong crossreaction with an F12 fimbrial subunit protein of human uropathogenic E. coli strains. Unlike human F12 fimbriae producing strains, the dog isolates did agglutinate dog erythrocytes in the presence of D-mannose but not human erythrocytes, indicating that the adhesin carried by these strains is different from the adhesin on fimbriae of human uropathogenic E. coli. Similar indications were obtained from experiments with latex beads coated with the receptor for P-fimbriae. These beads were agglutinated by Escherichia coli strains from human urinary tract infections, but not by the dog isolates described here. Preliminary adhesion experiments of human and dog Escherichia coli to human bladder epithelial and canine kidney epithelial cells also showed differences in adhesion depending on the origin of the strain tested.

Dot-blot hybridization method.

Nucleic acid hybridization is a very potent technique that can be used for the identification of DNA and RNA species with varying degree of homology and for the estimation of relative amounts of nucleic acid with known homolgy. In most cases, single-stranded (ss) (denatured) DNA or RNA is bound to a filter support (e.g., nitrocellulose) and incubated with a radioactively labeled ss DNA or RNA fragment ("probe") complementary to the nucleic acids of interest. In subsequent washing steps the nonhybridized probe is removed. Hybridized probe will be retained, but may be washed off in further washing steps, depending on the ion concentration and temperature of the wash.

Transformation in Escherichia coli: stages in the process.

Transformation experiments with Escherichia coli recipient cells and linear chromosomal deoxyribonucleic acid (DNA) are reported. E. coli can be rendered competent for DNA uptake by a temperature shock (0 degrees C leads to 42 degrees C leads to 0 degrees C) of the recipient cells in the presence of a high concentration of either Ca2+ or Mg2+ ions. Uptake of DNA into a deoxyribonuclease-resistant form, for which the presence of Ca2+ is essential, was possible during the temperature shock but appeared to occur most readily after the heat shock during incubation at 0 degrees C. When DNA was added to cells that had been heat shocked in the presence of divalent cations only, DNA uptake also occurred. This suggests that competence induction and uptake may be regarded as separate stages. Under conditions used to induce competence, we observed an extensive release of periplasmic enzymes, probably reflecting membrane damage induced during development of competence. After the conversion of donor DNA into a deoxyribonuclease-resistant form, transformants could be selected. It appeared that incubation, before plating, of the transformation mixture in a medium containing high Ca2+ and Mg2+ concentrations and supplemented with all growth requirements increased the transformation frequency. This incubation probably causes recovery of physiologically labile cells.

Nucleotide sequence of the origin of replication of the Escherichia coli K-12 chromosome.

The origin of replication, oriC, of the Escherichia coli chromosome was mapped within a DNA segment of 422 base pairs. The nucleotide sequence of this segment was determined. The source of DNA for the sequence analysis was a minichromosome constructed in vivo, consisting exclusively of chromosomal DNA and a minichromosome constructed by cloning in vitro. The nucleotide sequence of the replication origin is characterized by a high degree of repetitiveness due to both inverted and direct repeats. Sequence homologies were found between portions of the replication origins of E. coli and phages lambda and G4. This suggests similarities in some steps in the initiation of replication of the different replicons.

Mini-chromosomes: plasmids which carry the E. coli replication origin.

We have isolated plasmids by linking the 5.9 MD EcoRI fragment of E. coli that carries the origin of replication to an EcoRI fragment that carries an amplicillin resistance determinant, but lacks an origin of replication. 3 plasmids of this type, pOC1, pOC2, and pOC3, are described in detail in this report. Although the plasmids have some adverse effect on the growth properties of the host strain, their existence shows that two functioning chromosomal origins can coexist in one cell. Deletions generated from this type of plasmids allow an allocation of the origin of replication of E. coli within a DNA segment less than 0.4 MD in size.

Conjugation in Escherichia coli: a study of recombination and the fate of donor DNA at the level of the zygote.

We have developed an experimental system for studying concomitantly the fate of the donor DNA and the process of recombination after conjugation in Escherichia coli. We used a set of Hfr and F-strains carrying complementing lacZ mutations. Expression of the lacZ allele on the chromosomal fragment derived from the donor results in the formation of heat sensitive beta-galactosidase by complementation. By intragenic recombination between the two lacZ mutations a lacZ+ gene may be formed, and wild type beta-galactosidase will be synthesized subsequently. So the assay of heat sensitive and wild type beta-galactosidase enabled us to follow respectively the fate of the donor DNA and the recombination process. Using various recombination deficient recipient strains, we found that the donor DNA is progressively inactivated in recA, rec-34 and recH recipients, although the initial rate of expression is equivalent to that in a Rec+ recipient; no significant recombination was observed. In Rec+, recB or recG recipients there was no inactivation and recombination occurred. The kinetics of recombinant formation in the recB strain seems to differ from the wild type; in a recG recipient the recombination activity is significant, but lower than in the wild type recipient.