Quantitative profiling and identification of outer membrane proteins of beta-lactam resistant strain of Acinetobacter baumannii.

In the recent past, Acinetobacter baumannii in hospitals has become increasingly resistant to a number of antibiotics including the latest carbapenems and this is of great concern. Here, for the first time, we report 2D-Differential In-Gel Electrophoresis (DIGE) analysis of outer membrane proteome of ATCC 19606 and carbapenem-resistant strain of A. baumannii. Using biological variance analysis (BVA), we identified 25 differentially expressed proteins with a fold difference >or=2; confidence >90% and statistical significance p <or= 0.05. By applying MALDI TOF/TOF and ESI MS/MS proteomic approach to carbapenem-resistant A. baumannii, we identified four porins whose expression was significantly downregulated and a large number of upregulated proteins with specific transport and enzymatic properties. All the following synergistically give advantage to the resistant A. baumannii for survival: (i) high expression of altered CarO isoforms with possible low influx efficiency, (ii) elevated levels of CsuA/B with high adhesive properties, (iii) overexpression of pivotal nutrient transporters, (iv) continued expression of the major OmpAb, and (v) induced production of proteins of hypothetical origin. This proteomic study provides a platform to understand the complex nature of beta-lactam resistance in A. baumannii.