PAβN dihydrochloride

BACKGROUND: ;Since bacterial multidrug efflux pumps mediate intracellular photosensitizer methylene blue, a change in the expression alters the susceptibility to photoantimicrobial chemotherapy (PACT) of Pseudomonas aeruginosa, which may occur following repetitive sublethal challenges.;MATERIALS AND METHODS: ;We performed 10 consecutive, methylene blue-mediated PACT on one antibiotic-sensitive strain and three antibiotic-resistant strains of P. aeruginosa. Following each therapy, the surviving bacteria were collected for subsequent PACT. The susceptibility was compared for the pre- and the post-treated strains following repetitive PACT. To explore the existence of efflux pumps, one of the inhibitors, namely Phe-Arg β-naphthylamide dihydrochloride (PAβN 25 μg/ml), was added. Profiles of outer membrane proteins were obtained for the pre-treated and the post-treated strains.;RESULTS: ;The susceptibility of PACT did not correlate with the antibiotic sensitivity. Following ten PACT, there was no significant change in susceptibility for three tested strains, except for one antibiotic-resistant strain, for which the 10th generation became less susceptible than the original one. With 2-D electrophoresis, a change in the expression of outer membrane proteins was observed.

OBJECTIVES: ;The aim of this study was to characterize a putative novel macrolide efflux gene located in the vicinity of sul3 in porcine Escherichia coli.;METHODS: ;Five sul3-encoding E. coli isolates of porcine origin were investigated by plasmid characterization and random amplification of polymorphic DNA (RAPD) PCR. Unknown DNA adjacent to the sul3 genes was amplified using a PCR approach, followed by sequencing of the fragments. The putative macrolide efflux gene was cloned into pK18. The cloned gene was characterized by susceptibility testing by Etest in the presence and absence of efflux inhibitors.;RESULTS: ;Five sul3-encoding isolates, demonstrated to be unrelated by RAPD PCR, were characterized. The immediate genetic context of sul3 in five isolates was identical to that in plasmid pVP440, and in all cases, sul3 was associated with class 1 integrons. In three isolates, an open reading frame (orf2) encoding a putative protein with 38% amino acid identity to Mef(A) was found, while the two remaining isolates contained a fragment of orf2 truncated by IS26 insertion. In three of the isolates, this DNA region was demonstrated to be located on non-conjugative plasmids. When the complete orf2 was cloned, it conferred high-level resistance to erythromycin and azithromycin, and the resistance property could be partially inhibited using the efflux inhibitor Phe-Arg beta-naphthylamide dihydrochloride.

We investigated the mechanisms of resistance to carbapenems, aminoglycosides, glycylcyclines, tetracyclines, and quinolones in 90 multiresistant clinical strains of Acinetobacter baumannii isolated from two genetically unrelated A. baumannii clones: clone PFGE-ROC-1 (53 strains producing the OXA-58 β-lactamase enzyme and 18 strains with the OXA-24 β-lactamase) and clone PFGE-HUI-1 (19 strains susceptible to carbapenems). We used real-time reverse transcriptase PCR to correlate antimicrobial resistance (MICs) with expression of genes encoding chromosomal β-lactamases (AmpC and OXA-51), porins (OmpA, CarO, Omp33, Dcap-like, OprB, Omp25, OprC, OprD, and OmpW), and proteins integral to six efflux systems (AdeABC, AdeIJK, AdeFGH, CraA, AbeM, and AmvA). Overexpression of the AdeABC system (level of expression relative to that by A. baumannii ATCC 17978, 30- to 45-fold) was significantly associated with resistance to tigecycline, minocycline, and gentamicin and other biological functions. However, hyperexpression of the AdeIJK efflux pump (level of expression relative to that by A. baumannii ATCC 17978, 8- to 10-fold) was significantly associated only with resistance to tigecycline and minocycline (to which the TetB efflux system also contributed).