Horizontal transfer of the blaNDM-1 gene to Pseudomonas aeruginosa and Acinetobacter baumannii in biofilms

Horizontal gene transfer has contributed to the global spread of the bla(NDM-1) gene. Multiple studies have demonstrated plasmid transfer of bla(NDM-1) between Gram-negative bacteria, primarily Enterobacteriaceae species, but conjugational transfer of natural bla(NDM-1) plasmids from Enterobacteriaceae into Pseudomonas aeruginosa and Acinetobacter baumannii has not previously been shown. As P. aeruginosa and A. baumannii are both typically strong biofilm formers, transfer of natural bla(NDM-1) plasmids could potentially occur more readily in this environment. To determine whether natural bla(NDM-1) plasmids could transfer to P. aeruginosa or A. baumannii in biofilms, three clinical and environmental Enterobacteriaceae strains carrying NDM-1-encoding plasmids of different incompatibility types were mated with E. coli J53, producing E. coli J53-bla(NDM-1) transconjugants. Subsequently, dual-species biofilms were created using the E. coli J53 transconjugants as plasmid donors and either P. aeruginosa or A. baumannii as recipients. Biofilm transfer of NDM-encoding plasmids to P. aeruginosa and A. baumannii was successful from one and two E. coli J53-bla(NDM-1) transconjugants, respectively. This demonstrates the potential for the spread of bla(NDM-1), genes to P. aeruginosa and A. baumannii in clinical and environmental settings.