The relative and absolute fitness cost of resistance is a key biological parameter determining the rate of emergence and frequency of resistant bacteria in the community. The biological cost can be related to chromosomally localized resistance genes, or p lasmid-encoded resistance genes. So far, only very few studies have quantified the cost of transferred resistance genes. See our recent publication in Lancet Infectious Disease by Johnsen et al., (2011).
The hypothesis that will be tested in this projec t is that the transferred resistance genes (acquired experimentally) impose a biological cost and reduce the relative fitness of the recipient bacteria. We will use already established growth competition assays to numerically quantify fitness effects. The relative fitness of an antibiotic-resistant bacterium is determined by the relative rates at which resistant and sensitive bacteria grow and die (compete) in a defined environment. Other members of the research group in Tromsø are currently developing ma thematical models to predict the population dynamics of selected resistant bacteria in natural populations, based on such fitness estimates.
Tested hypothesis Antimicrobial resistance genes gained by horizontal gene transfer impose a biological cost and reduce the Malthusian fitness of bacteria that can be quantified experimentally in competition assays.
1) To determine the influence of different types of resistance genes (located in the same position in the bacterial genome) on th e relative fitness of the gram-negative bacterium Acinetobacter baylyi
2) To determine the correlations/association between fitness changes and the presence of multiple resistance gene combinations