**1. Introduction**

Since polymerase chain reaction (PCR) was invented in the mid-1980s, it has made its way into all molecular biology, genetic, microbiology or biochemistry laboratories, where it is, due to its simplicity and efficiency, used in a very wide range of (PCR)-based techniques and applications [1, 2]. In just a few hours with a certain amount of cycles consisting of three simple steps—DNA denaturation, annealing of primers and extension [2]—the desired DNA sequence is multiplied about a million fold [3]. The crucial step in PCR is the annealing of primers, where the annealing temperature determines the specificity of primer annealing. The annealing temperature of a standard PCR protocol is either 55°C [2, 3] or 60°C [4]. The chosen temperature depends on the strand-melting temperature of the primers and the desired specificity. For greater stringency higher temperatures are recommended [2].

PCR is very often used to amplify specific DNA fragments that are later cloned as inserts in plasmid vectors and used then in subsequent experiments. Examples of such subsequent experiments are nucleotide sequencing, in order to determine the nucleotide sequence of the insert or in vitro transcription, and translation, in order to obtain a certain protein.

In our experiments, the aim was to determine the nucleotide sequence of several fimbrial genes from different *Escherichia coli* (*E. coli*) strains isolated from faecal samples of dogs with diarrhoea. The genes of interest were *papA*, *papG*, *papEF* of the P-fimbriae and *F17G* of the F17-fimbriae. Therefore, from a collection of 24 clinical haemolytic *E. coli* strains from faecal samples of dogs with diarrhoea [5], genomic DNA was isolated and used as the matrix DNA to amplify these genes of interest with gene-specific primers with PCR. Further, the obtained PCR products were cloned into a TA cloning vector, and the nucleotide sequence was determined.
