Aminoglycoside resistance 16S rRNA methyltransferases block endogenous methylation, affect translation efficiency and fitness of the host

Competition experiments between susceptible and resistant strains. Competition was carried out in LB broth at 37°C. MM294 harboring (A) pGB2 and pGB2ΩarmA or pGB2ΩarmA* and (B) pGB2ΩnpmA were mixed at a 1:1 ratio at an initial inoculum of 10³ CFU and transferred every 12 h (corresponding to about 20 generations) in fresh medium for up to six passages. The competition index (CI) was calculated as the CFU ratio of the resistant and susceptible strains (R/S) at time (t₁) divided by the same R/S at time (t₀), and the selection coefficient s was then calculated as the slope of the following linear regression model s= ln(CI)/[t × ln(2)], where t is the number of generations. Values are the mean ± SE of at least three independent experiments.