Growth competition of macrolide-resistant and susceptible Helicobacter pylori strains

We examined population dynamics in a mixed culture of clonally related macrolide-resistant and -susceptible Helicobacter pylori strains isolated from a single patient. The resistant strain had a macrolide resistance-conferring A2143G mutation in the 23S rRNA gene. The growth rate of these two strains did not apparently differ when cultured separately. On the other hand, by conducting sequential passage of a mixed culture of the resistant and the susceptible strains, the ratio of the resistant strain to the susceptible strain in the culture typically decreased per passage, indicating that the resistance imposed a significant disadvantage on bacterial fitness in the population.