Multidrug efflux pumps are significant contributors to antimicrobial resistance in bacteria. Many efflux pump genes are found in the core genomes of a genus or species, suggesting that they have been vertically inherited in these lineages for a considerable time. Others appear to be associated with mobile genetic elements, such as plasmids and transposons and have a scattered distribution in sub-sets of phylogenetically distant strains, suggesting horizontal transfer between strains. Due to their lower level of conservation, horizontally acquired efflux pumps generally receive less attention than core pumps. However, these pumps may be especially problematic due to higher cellular expression and frequent genetic linkage to various alternative last line antibiotic resistance genes. Here I will describe our recent work leading to the identification and characterisation of a range of novel mobile efflux pump genes in pathogenic Acinetobacter lineages.