ases PpiA and PpiD. Accordingly, a major role of the Cpx response appears to be to maintain envelope protein folding status in the presence of adverse conditions. Molecular, biological and biochemical analysis of several Cpx signals supports the notion that most signals are specific. Therefore the Cpx system serves as an efficient model system to determine the mechanisms involved in signal transduction by a TCS, ranging from signal integration by the “20008854 target=’resource_window’> 22948146 kinase CpxA to the output response by CpxR. Studies have elucidated the different functions displayed by the Cpx system for example in envelope stress response system, pilus assembly, type III secretion, motility and chemotaxis, adherence, and biofilm development. Furthermore, the Cpx system is required for invasion of host cells in diverse pathogenic bacteria, including Escherichia coli, Salmonella enterica serovar Typhimurium, Shigella sonnei, Yersinia enterocolitica, and Legionella pneumophila. A recent study demonstrated that Xenorhabdus nematophilus requires the Cpx system both to colonize its nematode host and to kill larvae of the tobacco hornworm . Overall, the Cpx system of bacteria is known to be involved in maintenance, adapt and protection of the bacterial envelope in response to a variety of stressors, one such environmental assail that pathogenic bacteria for example E. coli, Salmonella spp., Enterobacter spp., Campylobacter spp., Acinetobacter spp., Pseudomonas spp., including Klebsiella spp., get exposed to is the pressure of antibiotics. Though the Cpx system has been implicated in the multidrug resistance of 
various human pathogens, however its direct involvement in JW-55 site regulating antimicrobial resistance has remained completely unexplored. Here, we initiated a systematic study to elucidate the direct role of Cpx TCS in conferring drug resistance by constructing a cpxAR deletion mutant in a notoriously drug resistant model organism; Klebsiella pneumoniae. K. pneumoniae are opportunistic pathogens and can give rise to severe diseases such as septicemia, pneumonia, urinary tract infections, and soft tissue infection. The hospitalized, immune compromised patient with underlying diseases is the main target of these bacteria. Thus, Klebsiella infections may serve as a paradigm of hospital-acquired infections. Their incidence of 5 to 7% of all hospital-acquired infections ranks them among the most important nosocomial pathogens. Klebsiella infections are not only responsible for nosocomial infections but also for community acquired infections such as severe liver abscesses. The capsular polysaccharide on their surface is the prime factor of virulence and toxicity in causing pyogenic liver abscess, with a high 1030% mortality rate globally. The K. pneumoniae NTUH-K2044 strain encapsulated with K1 hyper virulent antigen is usually isolated from clinical liver abscess patients. Increasingly, Klebsiella bacteria have developed antibiotic resistance, most recently to the class of antibiotics known as carbapenems. The MisT2 database has shown the presence of.466 signaling proteins in the 5,472,672 bp genome sequence of the K1 serotype . Though the biological functions of few TCS have been demonstrated previously; however the role of Cpx system has never been examined. Due to their central role in bacterial virulence regulation and their absence in animals including humans, TCS have been suggested as targets for antimicrobials, thus it is prudent to investigate their role in bacterial phys