Baer Participates In Cephalosporins Susceptibility By Regulating The Expression Level Of Outer Membrane Proteins In Escherichia Coli

The two-component system BaeSR participates in antibiotics resistance of Escherichia coli. To know whether the outer membrane proteins involve in the antibiotics resistance mediated by BaeSR, deletion of acrB was constructed and the recombined plasmid p-baeR was introduced into E. coli K12 and K12 Delta acrB. Minimum inhibitory concentrations (MICs) of antibacterial agents were determined by 2-fold broth micro-dilution method. Gene expressions related with major outer membrane proteins and multidrug efflux pump-related genes were determined by real-time quantitative reverse transcription polymerase chain reaction. The results revealed that the MICs of K12 Delta acrB to the tested drugs except for gentamycin and amikacin decreased 2- to 16.75-folds compared with those of K12. When BaeR was overexpressed, the MICs of K12 Delta acrB/p-baeR to ceftiofur and cefotaxime increased 2.5- and 2-fold, respectively, compared with their corresponding that of K12 Delta acrB. At the same time, the expression levels of ompC, ompF, ompW, ompA and ompX showed significant reduction in K12 Delta acrB/p-baeR as compared with K12 Delta acrB. Moreover, the expression levels of ompR, marA, rob and tolC also significantly 'decreased' in K12 Delta acrB/p-baeR. These findings indicated that BacR overproduction can decrease cephalosporins susceptibility in acrB-free E. coli by decreasing the expression level of outer membrane proteins.