The growing number of antibiotic resistant bacteria is becoming an increasing problem. The genes for resistance are often carried on mobile genetic elements that can spread rapidly through bacterial populations by horizontal gene transfer. Mechanisms of horizontal gene transfer include conjugation, the gene transfer between two bacteria that are in physical contact, which is considered the most important factor in the spread of resistant bacteria. A good characterisation of the factors that influence the conjugation frequency may lead to the discovery of new strategies to combat the resistant bacteria. These factors include bacterial defence mechanisms to control the entry of foreign DNA, such as CRISPR-Cas and restriction-modification (R-M) systems. The aim of this Master Theses was to determine whether there is a correlation between conjugation frequency of the plasmid pOX38:Cm and the presence of genes for CRISPR-Cas and R-M systems in recipient strains, incompatibility of plasmids in recipient and donor cell or antimicrobial production of recipient strains. CRISPR-Cas and R-M systems were determined using freely available computer programs (CRISPR-Cas++ and REBASE), but a correlation with the conjugation frequency was not discovered. Therefore we investigated the ability of the recipient to inhibit the growth of the donor (bacteriocinogenity assay) and the incompatibility between the plasmids in recipient cells and plasmid pOX38:Cm (BLAST). Some recipient strains formed lysis zones of the donor strain, but a correlation with the conjugation frequency did not exist. Comparison of the plasmids revealed no incompatibility between them. The observed differences in conjugation frequencies could not be explained by CRISPR-Cas or R-M systems, antimicrobial production or plasmid incompatibility.
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