**2. Conclusion**

Multidrug efflux pumps are primeval elements encoded in the microorganism's chromosomes which confer resistance to antibiotics at different levels: intrinsic resistance, acquired resistance, and transient induced phenotypic resistance. Additionally, multidrug efflux pumps exhibit various functions with relevance to bacterial adaptation to altered habitats. Some of these functions, like resistance to heavy metals, resemble antibiotic resistance, biocides, or solvents, as they are adaptive responses to diverse types of external injuries, whereas, others are associated to internal detoxification of intermediate toxic bacterial metabolites. AcrAB pump is an important antibiotic resistance determinant in bacterial pathogen, having a dynamic role in developing resistance towards carbapenem group of antibiotics and the role of regulatory genes in inducing the expression of these pumps highlights the fact that the regulators directly or indirectly involved in increasing the expression of efflux pump system leading towards the development of carbapenem resistant MDR *Escherichia coli* isolates in clinical settings.
