Investigation of potential genetic instability within the Helicobacter pylori genome

• Main Author: Cooper, Scott
• Published: University of East London 2001
• Subjects: 579.135
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487407

The human gastric pathogen Helicobacter pylori has been reported to be genetically diverse. However, initial research in this study indicated that the development of resistance to non-therapeutic antibiotics in vitro is comparable in frequency to other species of bacteria. Both spontaneous and induced mutation frequencies were found to be no higher than those observed in Escherichia coli. Conjugation experiments were performed between two type strains of H. pylori; one containing plasmid DNA of a conjugative size and the other being a plasmid-free antibiotic-resistant mutant, developed from earlier mutation studies. Following conjugation and antibiotic selection the isolates were screened for the presence of plasmid DNA. In initial studies, screening for plasmid DNA was performed using a non-radioactively labelled probe derived from plasmid DNA, in connection with Southern blotting / DNA hybridisation experiments. Due to problems with reproducibility, a simpler method was developed, using a PCR specific for H. pylori plasmid DNA, delivering consistent, accurate results. It was shown that conjugation occurred between these two H. pylori strains. Analysis of the 16S rDNA of a number of H. pylori strains was undertaken. Little genetic variation between isolates was observed in this study, using both nucleotide sequence data and restriction digest analysis. In a comparative study, the variation in 16S rDNA sequence observed between H. pylori isolates was found to be no greater than that observed between E.coli isolates. Despite all previous reports of genetic variability within the species, H. pylori did not display high mutation frequencies or a large amount of inherent genetic variability in this study. The discovery of conjugative DNA transfer does, however, suggest one possible mechanism for the generation of genetic variation and transfer of antibiotic resistance between H. pylori strains.