The mexCD-oprJ multidrug efflux operon of Pseudomonas aeruginosa is regulated by the NfxB repressor. Two forms of NfxB have been reported [Shiba et al. (1995). J Bacteriol 177, 5872) although mutagenesis studies here confirm that the larger protein (199 amino acids, 22.4 kDa) is the functional repressor. NfxB binds upstream of the mexCD-oprJ transcription initiation site to a region containing two inverted repeats, both of which are required for binding. Two-hybrid assays confirmed that NfxB is a multimer, with the C-terminal two-thirds of the repressor required for multimerization. Random mutagenesis identified several mutations within the C-terminal region of NfxB required for multimerization, all of which mapped to a three-helix subdomain of the C-terminal region in a structural model of the repressor, which may thus represent the multimerization domain. These mutations compromised NfxB binding to its target DNA in electromobility shift assays, and their introduction into the chromosome of P. aeruginosa enhanced mexCD-oprJ expression and promoted multidrug resistance, consistent with the functional NfxB repressor being a multimer. Site-directed and spontaneous nfxB mutants showing increased mexCD-oprJ expression and multidrug resistance were also recovered, with mutations mapping to the three-helix subdomain again impacting multimerization and DNA binding. Mutations mapping to the N-terminal helix-turn-helix motif implicated in DNA binding did not impact multimerization although they did render the repressor insoluble and unsuitable for mobility shift assays. Size exclusion column chromatography demonstrated that wild-type NfxB forms tetramers in solution, although a mutant form of the repressor carrying a G192D substitution near the C terminus of the protein and compromised for DNA binding and repressor activity forms dimers. These results suggest that NfxB operates as a tetramer (dimer of dimers) and that the C terminus of the protein serves as a tetramerization domain.

Compared to LRV-1-negative L. V. braziliensis, LRV-1-positive strains of L. V. braziliensis produced a predominant Th2-biased immune response, correlated in humans to poorer immunologic control of infection and more severe disease, including mucosal leishmaniasis. Effects of LRV-1 on the pathogenesis of American tegumentary leishmaniasis may be species specific.

Patients who received sBPBs for ambulatory wrist fracture surgery had a higher rate of unplanned health care resource utilization caused by pain after hospital discharge than those undergoing GA. These findings warrant confirmation in a prospective trial and emphasize the need for a defined postdischarge analgesic pathway as well as the potential merits of perineural home catheters.

mexCD-oprJ is an envelope stress-inducible multidrug efflux operon of Pseudomonas aeruginosa. A gene encoding a homologue of the NfxB repressor of this operon, PA4596, occurs downstream of oprJ and was proposed as a second repressor of this efflux operon. Inactivation of this gene had no impact on mexCD-oprJ expression in cells not exposed to envelope stress although its loss under envelope stress conditions yielded a > 10-fold increase in mexCD-oprJ expression. Consistent with PA4596 functioning as a mexCD-oprJ repressor, the purified protein was able to bind to a DNA fragment carrying the mexCD-oprJ promoter region. Expression of PA4596 was induced under conditions of envelope stress dependent on the AlgU envelope stress sigma factor, consistent with PA4596 operating under envelope stress conditions where it possibly serves to moderate envelope stress-inducible mexCD-oprJ expression. nfxB mutants showed elevated PA4596 expression and purified NfxB bound to DNA encompassing the PA4596 upstream region, an indication that NfxB functions as a repressor of PA4596 expression. Elimination of PA4596 in P. aeruginosa lacking nfxB and hyperexpressing mexCD-oprJ had no additional impact on mexCD-oprJ expression, regardless of the presence of envelope stress, suggesting that PA4596 repressor activity may be dependent on NfxB. This envelope stress-regulated repressor of mexCD-oprJ has been renamed esrC.