ile fatty acids, variations in pH and osmolarity, and competition with endogenous flora. The behaviour of the wild-type 17328890 strain and the cpxAR deficient mutants was therefore investigated under some of these hostile conditions to further understand how cpxAR interacts in the GI tract. E-strips were used to determine the precise MIC for different group of antibiotics such as amikacin, ampicillin, cefepime, cefotaxime, Halofuginone ceftazidime, ceftriaxone, chloramphenicol, ciprofloxacin, erythromycin, kanamycin, nalidixic acid, ofloxacin, polymyxin, rifampicin, tetracycline, tobramycin, trimethoprim, and vancomycin following 
the CLSI guidelines. a Fold change is the ratio of MICs for NTUH-K2044 and NTUH-K2044D cpxA. CpxAR Confers b-Lactam Resistance tors of MDR in K. pneumoniae are the efflux pumps belonging to MFS, RND, ATP binding cassette, small multidrug resistance, multidrug and toxic compound extrusion families. In K. pneumoniae NTUH-K2044, deletion of cpxAR resulted in loss of drug efflux capacity. The cpxAR deletion reduced the expression levels of efflux genes such as acrB, acrD and eefB in mutant when compared to wild type which indicates that possibly CpxR has a role in modulating the expression of MDR efflux pumps. Classical efflux pump comprises of an outer membrane protein that serves as a channel to regulate the exchange of extra and intra cellular substances which also includes antibiotics, detergents, dyes, organic solvents and bile acids. It was interesting to observe that the outer membrane protein profile of NTUHK2044DcpxAR had over expressed protein bands at,30 kDa,,22 22314911 kDa and,16 kDa. Recently, it has been reported that double deletion of OmpK35 and OmpK36 altered the MIC’s of b-lactams class of drugs in K. pneumoniae. Previous study has shown that the expression levels of outer membrane proteins STM1530 and OmpD, were influenced by the cpxAR TCS and it played important roles in mediating ceftriaxone resistance of S. Typhimurium. The notable differences in membrane profile prompted us to investigate the presence of CpxR binding sites in functionally characterized porins such as OmpC homolog in K. pneumoniae. Evidence for the CpxR protein binding on the promoter fragments of OmpCKP has been shown for the first time which well corroborate with the reports documented previously in other Gram negative bacteria. One striking feature of the predicted protein complement of K. pneumoniae is the presence of a disproportionately large number of regulatory proteins. Besides the presence of TCS there exists the presence of eukaryotic-type Ser/Thr kinase known as one component system in bacterial genomes. Recently, our group has identified the presence of one component system homologue in K. pneumoniae. Thus it is not only important to decode the regulatory cascade of the TCS but it is also imperative to understand the correlation between the one component system and TCS to get an overview of global signaling networks in clinically significant pathogens. Thus, characterizing the functions of CpxAR operon marks just the beginning by in itself. In summary, this study provides preliminary experimental evidence for the participation of cell envelope stress response system CpxAR in mediating resistance against GI stresses, antibiotics and disinfectants in K. pneumoniae NTUH-K2044; hyper virulent K1 serotype for the very first time. Materials and Methods Bacterial strains, plasmids and media K. pneumoniae NTUH-K2044 was kindly provided by Dr. Jin Tow