How might genes, such as those responsible for drug resistance, be transferred between bacterial species?
The genes that cause antibacterial resistance are transferred between the bacterial species through the reproductive process called bacterial conjugation. And also by horizontal gene transfer using plasmids, transposing or intergrons where the mutated or acquired antibiotic resistant gene is present.
Where could A. baumannii likely have acquired the genes for drug resistance?
A baumannii acquires its genes for drug resistance through horizontal gene transfer mechanism by transferring transposons from one A. baumannii to another A. baumannii bacterial cell where the transposons are incorporated into insertion sequences which make the antibiotic resistant.
General Background: About Antibiotic Resistance. (n.d.). Retrieved October 08, 2017, from https://emerald.tufts.edu/med/apua/about_issue/about_antibioticres.shtml