Mechanism of Quinolone Tolerance in Pseudomonas aeruginosa

The capacity of bacteria to survive, but not grow during antibiotic treatment may be defined as antibiotic tolerance. In bacteria, significant physiological changes occur depending on various environmental conditions ; low metabolic activity, slow growth, iron limitation and different stress conditions may be considered as factors playing a role in the tolerance to antimicrobial agents in Pseudomonas aeruginosa. One of the factors underlying these conditions is an alarmone, ppGpp that accumulates in the cells during transient starvation and nutritional deficiency. In order to investigate the possible role of ppGpp in the antibiotic tolerance in P. aeruginosa, the knockout mutants in the genes involved in the stringent response such as relA, spoT and dksA were constructed and investigated for their antibiotic susceptibility to quinolones. The susceptibility of these mutants to quinolone was determined using minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) testing and colony forming units per ml (CFU/ml). MIC/MBC ratios for ofloxacin in the dksA and the spoT knockout mutant were 1/4 and 0.5/2, respectively, in the comparison with the wild type strain, 1/1. The survival rate of the dksA and spoT knockout mutant in the presence of 8μg/ml of ofloxacin showed to be approximately 100 times higher than the same for the wild type strain. In the presence of 1μg/ml of ciprofloxacin, the survival rate for dksA and spoT mutant was 10-50 times higer than seen in the wild type strain. In comparison with the wild type, the relA and the relA spoT mutant displayed increased sensitivity to quinolones. The intracellular levels of ppGpp determined by high performance liquid chromatography (HPLC) demonstrated that spoT and dksA mutants possess higher basal levels of ppGpp. In conclusion, the data indicate that significantly elevated levels of ppGpp might be responsible for rendering these mutants tolerant to quinolones. The data presented in this study not only furnish some additional insights into the pleiotropic effect of ppGpp but also expand the importance of ppGpp as an antimicrobial target in P. aeruginosa. Moreover, given the facts that RpoN, an alternative sigma factor activates the expression of wide variety of environmentally regulated genes and is required for virulence in a variety of pathogens, we hypothesized that it might additionally be a target for interaction with antimicrobial agents. Two knockout mutants in the rpoN gene were constructed and investigated for their response to quinolone treatment. Using different construction approach, we obtained rpoN::Tc^r which displayed tolerance to quinolone and responded to quinolone addition by increased production of siderophore ; in addition, rpoN::Gm^r showed increased susceptibility to quinolone treatment. Results obtained imply that RpoN exerts its response to antibiotics through different pathways of regulation, and one of them might be due to the production of siderophore

Croatian SMEs: Current Stage and Prospect

Small businesses in Croatia are recognized as a locomotive for economic restructuring and increase of rate of employment. Bank credits have become more accessible in Croatia for the SME sector following privatization by foreign banks, which now participate with more than 90 percent in total bank assets of the country. Although foreign banks had a positive impact on the domestic banking market they tended to prefer household and large scale enterprise lending. Besides creating an equity gap, especially for the earlier stage non-technology based SMEs, asymmetric information leads to imperfect lending (credit rationing) even for prospective SMEs with fast revenue growth. SMEs\u27 role in banks lending decreases with bank size: small businesses have dominant place in small banks credit portfolio (cca 50% of credits). Furthermore, small business experience obstacles in assurance of appropriate bank finance. However, there is a trend among larger banks of paying greater attention to small businesses, as well as positive development in the variety of sources used for investment finance

LIBERALIZATION OF FINANCIAL SYSTEM IN CROTIA AND IN TURKEY

ABSTRAC

RpoN Mediates Tolerance to Tobramycin

Pseudomonas aeruginosa has developed diverse strategies to respond and adapt to antibiotic stress. Among the factors that modulate survival in the presence of antibiotics, alternative sigma factors play an important role. Here, we demonstrate that the alternative sigma factor RpoN (σ 54) promotes survival in the presence of tobramycin. The tobramycin-sensitive phenotype of logarithmic phase ΔrpoN mutant cells is suppressed by the loss of the alternative sigma factor RpoS. Transcriptional analysis indicated that RpoN positively regulates the expression of RsmA, an RNA-binding protein, in the P. aeruginosa stationary growth phase in a nutrient-rich medium. The loss of RpoS led to the upregulation of gacA expression in the nutrient-limited medium-grown stationary phase cells. Conversely, in the logarithmic growth phase, the ΔrpoS mutant demonstrated lower expression of gacA, underscoring a regulatory role of RpoS for GacA. Supplementation of tobramycin to stationary phase ΔrpoN mutant cells grown in nutrient-rich medium resulted in decreased expression of gacA, relA, and rpoS without altering the expression of rsmA relative to wild-type PAO1. The observed downregulation of gacA and relA in the ΔrpoN mutant in the presence of tobramycin could be reversed through the mutation of rpoS in the ΔrpoN mutant background. The tobramycin-tolerant phenotype of the ΔrpoNΔrpoS mutant logarithmic phase cells may be associated with the expression of relA, which remained unresponsive upon addition of tobramycin. The logarithmic phase ΔrpoS and ΔrpoNΔrpoS mutant cells demonstrated increased expression of gacA in response to tobramycin. Together, these results suggest that a complex regulatory interaction between RpoN, RpoS, the Gac/Rsm pathway, and RelA modulates the P. aeruginosa response to tobramycin

Measurement of Spin Density Matrix Elements in Λ(1520) Photoproduction at 8.2-8.8 GeV

We report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(1520)K+, via its subsequent decay to K−p. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with Eγ = 8.2 GeV–8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, − (t − t0). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in Λ(1520) photoproduction

Search for Photoproduction of Axionlike Particles at GlueX

We present a search for axionlike particles, a, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the a-gluon coupling is dominant. The search uses a → γγ and a → π+π−π0 decays, and a data sample corresponding to an integrated luminosity of 168  pb−1 collected with the GlueX detector. The search for a → γγ decays is performed in the mass range of 180 \u3c ma \u3c480  MeV, while the search for a → π+π−π0 decays explores the 600 \u3c ma \u3c 720  MeV region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the a-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered

Enhancement activity of QS autoinducer analog

In this study, we have investigated the effects of the newly synthesized analog of Pseudomonas aeruginosa quorum-sensing autoinducer named AIA-1 (autoinducer analog) against antibiotic-resistant bacteria. In vitro susceptibility and killing assays for P. aeruginosa PAO1ΔoprD mutant and clinical isolates were performed by using antibiotics and AIA-1. In an in vivo assay, a luminescent carbapenem-resistant strain derived from PAO1ΔoprD was injected into neutropenic ICR mice and bioluminescence images were acquired after the treatment with antibiotics and AIA-1. Additionally, we investigated the effects of the combination use against carbapenem- resistant Enterobacteriaceae (CRE). Using killing assays in P. aeruginosa, the survival rates in the presence of antibiotics and AIA-1 significantly decreased in comparison with those with antibiotics alone. Furthermore, dual treatment of biapenem and AIA-1 was more effective than biapenem alone in a mouse infection model. AIA-1 did not change the MICs in P. aeruginosa, suggesting that AIA-1 acts on the mechanism of antibiotic tolerance. Conversely, the MICs of antibiotics decreased in the presence of AIA-1 in some CRE strains, indicating that AIA-1 may require additional mechanism to act on CRE. In conclusion, AIA-1 may be a potent drug for clinical treatment of infections caused by antibiotic-resistant bacteria

Measurement of the J/ψ\psi photoproduction cross section over the full near-threshold kinematic region

We report the total and differential cross sections for $J/\psi$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/\psi$ photoproduction and its relation to the $J/\psi-$proton interaction. These measurements of $J/\psi$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states.Comment: 15 pages 18 figure