Small things matter : of phages and antibiotic resistance conferring plasmids

Abstract

Viruses and plasmids are small units of genetic material dependent on cells either transiently or continuously. Intriguingly, stories of these small entities intertwine in antibiotic resistance crisis. Horizontal gene transfer enables bacteria to respond rapidly to chances in their environment. Anthropogenic consumption of antibiotics induces the travel of resistance encoding genes mainly as passengers of conjugative plasmids. In this thesis, I demonstrate that clinically important resistance plasmids could evolutionarily rescue susceptible bacteria under lethal antibiotic concentrations. If mobile resistance genes are available in surrounding community, administration of high doses of antibiotic might not be enough to treat some bacterial infections – calling for alternatives to fight multi-resistant bacteria and interfere the spread and maintenance of resistance. Phage therapy, utilization of bacterial viruses against bacteria, could be one such avenue. In this thesis plasmid-depended phage PRD1 was studied in itself and as a tool to be utilized against resistance plasmid carrying bacteria. Blue native polyacrylamide gel electrophoresis revealed interaction between two virus entry related membrane proteins and zymogram analysis overruled a previous model of the lytic enzyme residing at the genome-packaging vertex. Bacterial resistance to PRD1 was linked with either lost or impaired conjugation ability, that could restore only when the initial resistance-conferring mutation was a dynamic tandem repeat insertion. Promisingly, the reversion also returned the susceptibility to the phage. Yet, as plasmid-dependent phages are currently available only against some resistance plasmids, an alternative approach, on-demand isolation of phages, was investigated against common nosocomial pathogens. Staphylococcus, Acinetobacter and Enterococcus phages were scarce in the environmental reservoir whereas phages against E. coli, K. pneumoniae, P. aeruginosa and Salmonella strains could often be isolated as needed. Altogether, different manifestations of phage-therapy may provide answers to the current antibiotic resistance crisis.