The role of RND-type efflux pumps in multidrug-resistant mutants of Klebsiella pneumoniae

The emergence of multidrug-resistant Klebsiella pneumoniae is a worldwide problem. K. pneumoniae possesses numerous resistant genes in its genome. We isolated mutants resistant to various antimicrobials in vitro and investigated the importance of intrinsic genes in acquired resistance. The isolation frequency of the mutants was 10(-7)-10(-9). Of the multidrug-resistant mutants, hyper-multidrug-resistant mutants (EB256-1, EB256-2, Nov1-8, Nov2-2, and OX128) were identified, and accelerated efflux activity of ethidium from the inside to the outside of the cells was observed in these mutants. Therefore, we hypothesized that the multidrug efflux pump, especially RND-type efflux pump, would be related to changes of the phenotype. We cloned all RND-type multidrug efflux pumps from the K. pneumoniae genome and characterized them. KexEF and KexC were powerful multidrug efflux pumps, in addition to AcrAB, KexD, OqxAB, and EefABC, which were reported previously. It was revealed that the expression of eefA was increased in EB256-1 and EB256-2: the expression of oqxA was increased in OX128; the expression of kexF was increased in Nov2-2. It was found that a region of 1,485 bp upstream of kexF, was deleted in the genome of Nov2-2. K. pneumoniae possesses more potent RND-multidrug efflux systems than E. coli. However, we revealed that most of them did not contribute to the drug resistance of our strain at basic levels of expression. On the other hand, it was also noted that the overexpression of these pumps could lead to multidrug resistance based on exposure to antimicrobial chemicals. We conclude that these pumps may have a role to maintain the intrinsic resistance of K. pneumoniae when they are overexpressed. The antimicrobial chemicals selected many resistant mutants at the same minimum inhibitory concentration (MIC) or a concentration slightly higher than the MIC. These results support the importance of using antibiotics at appropriate concentrations at clinical sites

An evaluation to define the role of repeat transurethral resection in a treatment algorithm for non-muscle-invasive bladder cancer

Objective: Repeat transurethral resection (ReTUR) is an effective treatment for non-muscle-invasive bladder cancer (NMIBC) to prevent disease recurrence or progression. It also has an important role in stratifying patients according to histopathological results. Therefore, the end point of ReTUR should be considered in a treatment algorithm. We evaluated positive ReTUR to define its role in a treatment algorithm for NMIBC. Materials and Methods: A second TUR was performed in 111 patients between July 2006 and February 2010. A third TUR was performed in 31 patients with T1/a/is tumors at the second TUR. The incidence of residual disease was calculated according to the NMIBC risk levels proposed by the International Bladder Cancer Group. We used ReTUR as a general term to indicate second and third TURs. Results: Residual disease at the second TUR was detected in 51% of the patients; it was observed in 17%, 45%, and 65% patients in the low-, intermediate-, and high-risk disease groups, respectively (P = 0.01). Residual disease at the third TUR was detected in 48% patients; it was observed in 18% and 65% patients in the intermediate- and high-risk disease groups, respectively (P = 0.06). Conclusion: The incidence of residual disease correlated with the risk levels for NMIBC. In the intermediate-risk disease group, nearly complete resection was accomplished after the third TUR. However, in the high-risk disease group, a high incidence of residual disease was identified even after the third TUR. Our results provide important data that may be useful in establishing an end point in a treatment algorithm for NMIBC