Sugar and hexokinase suppress expression of PIP aquaporins and reduce leaf hydraulics that preserves leaf water potential.

Sugars affect central aspects of plant physiology, including photosynthesis, stomatal behavior and the loss of water through the stomata. Yet, the potential effects of sugars on plant aquaporins (AQPs) and water conductance have not been examined. We used database and transcriptional analyses, as well as cellular and whole-plant functional techniques to examine the link between sugar-related genes and AQPs. Database analyses revealed a high level of correlation between the expression of AQPs and that of sugar-related genes, including the Arabidopsis hexokinases 1 (AtHXK1). Increased expression of AtHXK1, as well as the addition of its primary substrate, glucose (Glc), repressed the expression of 10 AQPs from the plasma membrane-intrinsic proteins (PIP) subfamily (PIP-AQPs) and induced the expression of two stress-related PIP-AQPs. The osmotic water permeability of mesophyll protoplasts of AtHXK1-expressing plants and the leaf hydraulic conductance of those plants were significantly reduced, in line with the decreased expression of PIP-AQPs. Conversely, hxk1 mutants demonstrated a higher level of hydraulic conductance, with increased water potential in their leaves. In addition, the presence of Glc reduced leaf water potential, as compared with an osmotic control, indicating that Glc reduces the movement of water from the xylem into the mesophyll. The production of sugars entails a significant loss of water and these results suggest that sugars and AtHXK1 affect the expression of AQP genes and reduce leaf water conductance, to coordinate sugar levels with the loss of water through transpiration.

A novel approach in the management of right-sided endocarditis: percutaneous vegectomy using the AngioVac cannula.

The AngioVac is a vacuum-based device introduced in 2012 to percutaneously remove undesirable material from the intravascular system. In scattered reports, the AngioVac has been used for removal of device-led vegetations and right-sided thrombi. In this article, we describe three cases of right-sided endocarditis treated with AngioVac: a mobile mass extending from the vena cava into the right atrium, large native tricuspid vegetations, and bioprosthetic tricuspid vegetations. This device shows benefit in reducing vegetation load, decreasing septic lung embolization, and reducing reinfection in active intravenous drug users. These cases exhibit the AngioVac's arrival as a new and exciting tool in endocarditis treatment, providing an alternative to open surgery and accessorizing antimicrobial treatment.

Intravenous Tigecycline Facilitates Cure of Severe Clostridium difficile Infection (CDI) After Failure of Standard Therapy: A Case Report and Literature Review of Tigecycline Use in CDI.

Standard treatment for severe Clostridium difficile infection (CDI) is oral vancomycin with metronidazole. After failure of this standard regimen, treatment becomes challenging. A young woman treated for septic shock developed CDI. Standard treatment failed and she was ineligible for fecal transplant. Addition of tigecycline to her regimen resulted in cure.

The role of plasma membrane aquaporins in regulating the bundle sheath-mesophyll continuum and leaf hydraulics.

Our understanding of the cellular role of aquaporins (AQPs) in the regulation of whole-plant hydraulics, in general, and extravascular, radial hydraulic conductance in leaves (K(leaf)), in particular, is still fairly limited. We hypothesized that the AQPs of the vascular bundle sheath (BS) cells regulate K(leaf). To examine this hypothesis, AQP genes were silenced using artificial microRNAs that were expressed constitutively or specifically targeted to the BS. MicroRNA sequences were designed to target all five AQP genes from the PLASMA MEMBRANE-INTRINSIC PROTEIN1 (PIP1) subfamily. Our results show that the constitutively silenced PIP1 (35S promoter) plants had decreased PIP1 transcript and protein levels and decreased mesophyll and BS osmotic water permeability (P(f)), mesophyll conductance of CO2, photosynthesis, K(leaf), transpiration, and shoot biomass. Plants in which the PIP1 subfamily was silenced only in the BS (SCARECROW:microRNA plants) exhibited decreased mesophyll and BS Pf and decreased K(leaf) but no decreases in the rest of the parameters listed above, with the net result of increased shoot biomass. We excluded the possibility of SCARECROW promoter activity in the mesophyll. Hence, the fact that SCARECROW:microRNA mesophyll exhibited reduced P(f), but not reduced mesophyll conductance of CO2, suggests that the BS-mesophyll hydraulic continuum acts as a feed-forward control signal. The role of AQPs in the hierarchy of the hydraulic signal pathway controlling leaf water status under normal and limited-water conditions is discussed.

Water Balance, Hormone Homeostasis, and Sugar Signaling Are All Involved in Tomato Resistance to Tomato Yellow Leaf Curl Virus.

Vacuolar water movement is largely controlled by membrane channels called tonoplast-intrinsic aquaporins (TIP-AQPs). Some TIP-AQP genes, such as TIP2;2 and TIP1;1, are up-regulated upon exposure to biotic stress. Moreover, TIP1;1 transcript levels are higher in leaves of a tomato (Solanum lycopersicum) line resistant to Tomato yellow leaf curl virus (TYLCV) than in those of a susceptible line with a similar genetic background. Virus-induced silencing of TIP1;1 in the tomato resistant line and the use of an Arabidopsis (Arabidopsis thaliana) tip1;1 null mutant showed that resistance to TYLCV is severely compromised in the absence of TIP1:1. Constitutive expression of tomato TIP2;2 in transgenic TYLCV-susceptible tomato and Arabidopsis plants was correlated with increased TYLCV resistance, increased transpiration, decreased abscisic acid levels, and increased salicylic acid levels at the early stages of infection. We propose that TIP-AQPs affect the induction of leaf abscisic acid, which leads to increased levels of transpiration and gas exchange, as well as better salicylic acid signaling.

Differential tissue-specific expression of NtAQP1 in Arabidopsis thaliana reveals a role for this protein in stomatal and mesophyll conductance of CO2 under standard and salt-stress conditions.

The regulation of plant hydraulic conductance and gas conductance involves a number of different morphological, physiological and molecular mechanisms working in harmony. At the molecular level, aquaporins play a key role in the transport of water, as well as CO2, through cell membranes. Yet, their tissue-related function, which controls whole-plant gas exchange and water relations, is less understood. In this study, we examined the tissue-specific effects of the stress-induced tobacco Aquaporin1 (NtAQP1), which functions as both a water and CO2 channel, on whole-plant behavior. In tobacco and tomato plants, constitutive overexpression of NtAQP1 increased net photosynthesis (A(N)), mesophyll CO2 conductance (g(m)) and stomatal conductance (g(s)) and, under stress, increased root hydraulic conductivity (L(pr)) as well. Our results revealed that NtAQP1 that is specifically expressed in the mesophyll tissue plays an important role in increasing both A(N) and g(m). Moreover, targeting NtAQP1 expression to the cells of the vascular envelope significantly improved the plants' stress response. Surprisingly, NtAQP1 expression in the guard cells did not have a significant effect under any of the tested conditions. The tissue-specific involvement of NtAQP1 in hydraulic and gas conductance via the interaction between the vasculature and the stomata is discussed.

Tackling antibiotic resistance.

The development and spread of antibiotic resistance in bacteria is a universal threat to both humans and animals that is generally not preventable but can nevertheless be controlled, and it must be tackled in the most effective ways possible. To explore how the problem of antibiotic resistance might best be addressed, a group of 30 scientists from academia and industry gathered at the Banbury Conference Centre in Cold Spring Harbor, New York, USA, from 16 to 18 May 2011. From these discussions there emerged a priority list of steps that need to be taken to resolve this global crisis.

Accuracies of beta-lactam susceptibility test results for Pseudomonas aeruginosa with four automated systems (BD Phoenix, MicroScan WalkAway, Vitek, and Vitek 2).

Contemporary clinical isolates and challenge strains of Pseudomonas aeruginosa were tested by four automated susceptibility testing systems (BD Phoenix, MicroScan WalkAway, Vitek, and Vitek 2; two laboratories with each) against six broad-spectrum beta-lactams, and the results were compared to reference broth microdilution (BMD) and to consensus results from three validated methods (BMD, Etest [AB Biodisk, Solna, Sweden], and disk diffusion). Unacceptable levels of error (minor, major, and very major) were detected, some with systematic biases toward false susceptibility (piperacillin-tazobactam and imipenem) and others toward false resistance (aztreonam, cefepime, and ceftazidime). We encourage corrective action by the system manufacturers to address test biases, and we suggest that clinical laboratories using automated systems should consider accurate alternative methods for routine use.

Improvements in antimicrobial prescribing for treatment of upper respiratory tract infections through provider education.

BACKGROUND: Inappropriate use of antimicrobials to treat acute upper respiratory tract infections (URIs), which usually have a viral etiology, contributes to emergence and spread of antimicrobial resistance in Streptococcus pneumoniae and other human bacterial pathogens. OBJECTIVE: To reduce antimicrobial use for management of acute URIs in adult and pediatric patients. DESIGN: Prospective, nonrandomized, controlled trial. SETTING: Four primary care clinics within a staff model HMO in Detroit, Mich. PARTICIPANTS: Twenty-one primary care physicians at clinics where the educational intervention was implemented, and 9 primary care physicians at control clinics where no educational programs were implemented. MEASUREMENTS: Antibiotic prescribing for acute URIs during the baseline and study years among the intervention and control groups. RESULTS: A generalized linear mixed-effects model was used and showed that antimicrobial prescribing among the intervention group physicians decreased 24.6% from the baseline to the postintervention period (P<.0001) for both pediatric and adult medicine physicians. From the baseline to the study period, there was no significant decline in rates of antimicrobial prescribing by the control group of physicians (pediatricians, P=.35; internists, P=.42). The rates of decline in antimicrobial prescribing differed significantly between the intervention and control groups (P<.0003 for pediatricians and P<.01 for Internists). CONCLUSIONS: An interactive, case-based educational program for physicians and their staff proved effective for reducing unwarranted prescribing of antibiotics in the treatment of URIs by primary care physicians in a Medicaid HMO setting.

Purification, crystallization and preliminary X-ray analysis of Enterococcus faecium aminoglycoside-2''-phosphotransferase-Ib [APH(2'')-Ib].

Bacterial resistance to the aminoglycoside antibiotics is primarily the result of deactivation of the drugs. Three families of enzymes are responsible for this activity, with one such family being the aminoglycoside phosphotransferases (APHs). The gene encoding one of these enzymes, APH(2'')-Ib, has been cloned and the protein (comprising 299 amino-acid residues) expressed in Escherichia coli, purified and crystallized in the presence of 16%(w/v) PEG 3350 and gentamicin. The crystals belong to the monoclinic space group P2(1), with approximate unit-cell parameters a = 79.7, b = 58.8, c = 81.4 A, beta = 98.4 degrees, and preliminary X-ray diffraction analysis is consistent with the presence of two molecules in the asymmetric unit. Synchrotron diffraction data to approximately 2.65 A resolution were collected from a native APH(2'')-Ib crystal at beamline BL9-2 at SSRL (Stanford, CA, USA). Selenium-substituted crystals have also been produced and structure determination is proceeding.

Multiplex PCR for detection of aminoglycoside resistance genes in enterococci.

A multiplex PCR procedure for detecting the aminoglycoside resistance genes aac(6')-Ie-aph(2")-Ia, aph(2")-Ib, aph(2")-Ic, aph(2")-Id, aph(3')-IIIa, and ant(4')-Ia was evaluated and found to determine accurately the presence of these genes in enterococci.

Mutations in the aph(2")-Ic gene are responsible for increased levels of aminoglycoside resistance.

Random PCR mutagenesis of the enterococcal aph(2")-Ic gene followed by selection for mutant enzymes that confer enhanced levels of aminoglycoside resistance resulted in mutants of APH(2")-Ic with His-258-Leu and Phe-108-Leu substitutions, all of which conferred rises in the MICs of several aminoglycosides. The mutated residues are located outside conserved regions of aminoglycoside phosphotransferases.

Mutational replacement of Leu-293 in the class C Enterobacter cloacae P99 beta-lactamase confers increased MIC of cefepime.

The class C beta-lactamase from Enterobacter cloacae P99 confers resistance to a wide range of broad-spectrum beta-lactams but not to the newer cephalosporin cefepime. Using PCR mutagenesis of the E. cloacae P99 ampC gene, we obtained a Leu-293-Pro mutant of the P99 beta-lactamase conferring a higher MIC of cefepime (MIC, 8 microg/ml, compared with 0.5 microg/ml conferred by the wild-type enzyme). In addition, the mutant enzyme produced higher resistance to ceftazidime but not to the other beta-lactams tested. Mutants with 15 other replacements of Leu-293 were prepared by site-directed random mutagenesis. None of these mutant enzymes conferred MICs of cefepime higher than that conferred by Leu-293-Pro. We determined the kinetic parameters of the purified E. cloacae P99 beta-lactamase and the Leu-293-Pro mutant enzyme. The catalytic efficiencies (k(cat)/K(m)) of the Leu-293-Pro mutant beta-lactamase for cefepime and ceftazidime were increased relative to the respective catalytic efficiencies of the wild-type P99 beta-lactamase. These differences likely contribute to the higher MICs of cefepime and ceftazidime conferred by this mutant beta-lactamase.