Fitness costs of blaNDM-1 bearing plasmid pNDM-BJ01 in Acinetobacter lwoffii

Abstract:

Abstract:［Objective］To investigate the fitness costs of the New Delhi Metallo-β-lactamase-1 (blaNDM-1) bearing plasmid pNDM-BJ01 in Acinetobacter lwoffii strain 10621，and to evaluate the potentials of the sustainability and expansions among the Acinetobacter lwoffii population.［Methods］We obtained the spontaneous mutant of A. lwoffii missing pNDM-BJ01，10621NDM-1(－) via serial passages of the wild strain 10621NDM-1(+) on the antibiotics-free media. We then compared the in vitro fitness of these two strains by measuring the growth curves，the ability of biofilm formation and the survival rates in nutrient-free PBS buffer．［Results］Plasmid pNDM-BJ01 was unstable in A． lwoffii strain 10621，and 11 passages will be enough to get it deleted from the ancestral strain．We found no significant difference in the growth curves either at 26 or 37°C for 10621NDM-1(+) and 10621NDM-1(－)．The biofilm formation ability of the plasmid free derivate 10621NDM-1(－) was significant higher than its resistant ancestor 10621NDM-1(+) at 26°C，whereas the latter showed higher ability of biofilm formation at 37°C． Strain 10621NDM-1(+) was vulnerable in the nutrient-free PBS buffer，with less than 5% survival rate on the first day and dying out on the sixth day，whereas 10621NDM-1(－) survived till the seventh day.［Conclusion］blaNDM-1 bearing plasmid pNDM-BJ01 possesses significant fitness costs in A. lwoffii strain 10621，and it will get depleted easily if the antibiotic press released. pNDM-BJ01-free 10621NDM-1(－) strain has higher fitness than its ancestor，10621NDM-1(+)，which implies the limited expansion potential of plasmid pNDM-BJ01 in A. lwoffii.