Differential expression of Outer membrane proteins in early stages of meropenem-resistance in Acinetobacter baumannii
Acinetobacter baumannii has emerged as one of the six most important drug-resistant microbes in the world. Resistance by A. baumannii to β-lactams and in particular to meropenem is a serious concern. In this connection, it is essential to understand the changes in the outer membrane proteome of A. baumannii in the initial stages of resistance. For this we have chosen one low resistant strain with MIC of 32 μg/ml and one intermediate strain with very low MIC of 0.8 μg/ml of meropenem and compared their outer membrane profiles with that of sensitive strain, ATCC 19606 of A. baumannii. Decreased expression of porins, transporters and increased production of metabolic enzymes like Succinyl-CoA synthetase, enoyl-CoA hydratase is a common feature in both intermediate strain and low resistant strains. Interestingly, the differential protein expression levels showed a direct relationship with increasing meropenem resistance. It is clear that initial exposure to meropenem resistance drives A. baumannii to restrict the production of OmpAb, CarO, transporters, while the upregulation of genes of altered CarO, metabolic enzymes, peroxidines and antioxidant protein assist in the survival of the bacterium. Because of these unique features of adaptation combined with high metabolic changes in response to antibiotic pressure, A. baumannii poses challenges in therapeutic strategies.