ProjektportalEvolution of ESBL activity in horizontally transferring ?-lactamase genes
Terrmin
VT22
Beskrivning
In my group we use experimental evolution to study different questions in evolutionary biology, particularly regarding how new functions arise and evolve. It has been argued that horizontal gene transfer (HGT) is the main driver of evolution and the appearance of new functions in bacteria. However, irrespective of how a gene finds its way into an organism, at some point it has to have evolved before being mobilized by HGT, and mobilized genes continue to evolve new functions. This becomes obvious when e.g. considering the vast variety of ?-lactamases with different substrate specificities that has evolved from a small number of ancient ?-lactamases since penicillin was first introduced in the clinics in the 1940s.
TEM-1 ?-lactamase confers high level resistance towards penicillins and 1st generation cephalosporin antibiotics, but has only minor activities towards 2nd and 3rd generation cephalosporins. After the introduction of 2nd and 3rd generation cephalosporins in clinical use, many ESBL variants capable of hydrolyzing 2nd or 3rd generation cephalosporins has evolved from TEM-1.
In previous experimental studies people have tried to study the evolution of new functions in ?-lactamases by prolonged selection of bacterial populations carrying TEM-1 or other ?-lactamases. Much of the gain in resistance in these studies has been by mutations that limit uptake or increase efflux of the antibiotic, and only a minority of mutations have affected the actual ?-lactamases.
One difference between these experiments and what happens in natural evolution is that in natural evolution the genes encoding ?-lactamases are often present on plasmids or other mobile elements that are capable of spreading horizontally. If the ?-lactamase gene is transferred to a new host often enough and encounters selection for ESBL activity, perhaps selection will favor evolution of the ?-lactamase gene instead of the rest of the host genome.
The purpose of this project is to test the idea that evolution of ESBL activity in TEM-1 becomes more likely if horizontal transfer is allowed.
Methods that will be used:
Experimental evolution by serial passage in medium with different ?-lactam antibiotics
Generalized transductions for horizontal transfer
Antibiotic susceptibility testing (E-tests)
As model organism we will use a Salmonella enterica strain carrying the blaTEM-1 gene and an inducible P22 prophage for high efficiency of generalized transduction.
Huvudområde
Farmaceutisk vetenskap
Ämne
Mikrobiologi, infektionsbiologi
Typ
Laborativ studie
Företag
Institutionen för Medicinsk Biokemi och Mikrobiologi
Ort/Plats
Uppsala
Handledarens namn
Joakim Näsvall
Handledarens e-post
joakim.nasvall@imbm.uu.se
Institution
Program
Kurs
Omfattning/hp
30hp
Hur många studenter kan antagas för detta projekt?
1