Transduction in Staphylococcus aureus

PhD-student: Ahlam Alsaadi
Thesis defended: 18 May 2021

In Staphylococcus aureus is a pathogenic bacterium that able to infect humans and animals. Third of healthy human population carries Staphylococcus aureus in their interior nares, while the rest are intermittent carriers. S. aureus are able to develop antibiotic resistance mechanisms for their ability to obtain DNA from their surroundings via various horizontal gene transfer mechanisms such as transduction. In S. aureus, bacteriophages “phages in short”, are bacterial viruses, that infect and lyse the bacteria are also mediate the genetic material exchange via transduction process.

Phages are widespread, their biology and interaction with their hosts has been extensively studied, yet there is much to uncover. There are two types of phages exist in the environment, temperate phages, in which integrate their genome into the bacterial chromosome, and virulent phages, in which develop a productive infection and kills the bacteria. In S. aureus, temperate phages are common and can be found from one up to nine prophages, integrated phages, in sequenced S. aureus genomes. These temperate phages are able to encode toxins and virulence factors while shuffling antibiotic resistance genes between strains.

To look into the phage and bacteria interaction and understand the influence that either the bacterial genes and/or the phage have on their interaction. 

I have investigated how bacterial viruses (phages) transfer bacterial DNA between cells by a process termed transduction and how this affects the ability of bacteria and phages to survive adverse conditions. In the human pathogen, Staphylococcus aureus I followed transfer of antibiotic resistance genes between cells and found that for phages, that as part of their lifestyle is integrated in the bacterial genome, benefit from transduction of antibiotic resistance genes when the bacteria are exposed to antibiotics. The phages residing in bacterial genomes are termed pro-phages and my work furthermore revealed that bacterial genes affect the stability of prophages. Thus, this suggests that there is close collaboration between phage and bacterium and that these interactions can lead to dissemination of antibiotic resistance genes between bacteria. Overall, the research conducted for this thesis expands the current knowledge on transduction and related processes in S. aureus and it points to a symbiotic relationship between phages and bacteria.