COLISTIN RESISTANCE IN CARBAPENEM-RESISTANT KLEBSIELLA PNEUMONIAE STRAINS

Objective: There is an increasing use of colistin consequent to increase in the infections caused by carbapenem-resistant Klebsiella pneumoniae.The present study was conducted to determine the minimum inhibitory concentration (MIC) of colistin and the resistance pattern of colistin in carbapenem-resistant K. pneumoniae (CRKP) strains in our intensive care unit (ICU).Methods: Antibiotic susceptibility testing for other antimicrobial agents was done by Kirby-Bauer disk diffusion method. MIC of colistin was determined by agar dilution method. The results of antibiotic susceptibility testing were interpreted as per Clinical Laboratory Standard Institute guidelines 2016 and MIC of colistin were interpreted as per European Committee on Antimicrobial susceptibility testing. The carbapenem resistance was phenotypically detected by modified hodge test and imipenem/imipenem ethylenediaminetetraacetic acid disk method.Results: Out of 518 K. pneumoniae, 329 were resistant to carbapenems, and 91 isolates showed resistance to colistin. The MIC of colistin ranged between 4 and >512 ug/ml and MIC90 was 16 ug/L and MIC50 was 4 ug/ml. A majority of the colistin-resistant isolates were found in multidisciplinary ICU (85/91).Conclusion: The emergence of colistin-resistant strains is a major problem due to limited treatment options for infections caused by CRKP carbapenemase producing K. pneumoniae. Colistin should not be used alone, combination therapy should be preferred

Connecting the dots: Path model to identify key phenotypic traits for screening plants with tolerance to nitrogen deficiency.

Varieties that tolerate low nitrogen (N) application rates can reduce fertilizer costs, minimize nitrate leaching and runoff losses, and lower overall CO2 emissions associated with fertilizer manufacturing. The goal of our research is to show the usefulness of path models to identify key phenotypic traits for screening plants with a tolerance to low N application rates. We grew tolerant and sensitive cultivars of poinsettia (Euphorbia pulcherrima) using a water-soluble fertilizer (15-5-15 Cal Mag) in both optimal (electrical conductivity of 2.5 dS·m-1) and N-deficient (electrical conductivity of 0.75 dS·m-1) treatments and measured 24 different traits at the cellular, leaf, and whole-plant scales in both cultivars and treatments. The experiment was laid out as a split-plot design with N treatments as main plots and cultivars as sub-plots, with five replications. Path analysis was conducted to develop sequential relationships among these traits. Statistical comparisons between tolerant and sensitive cultivars in the N-deficient treatment indicated an increase in shoot biomass (19.9 vs 14.4 g), leaf area (2775 vs 1824 cm2), leaf dry weight (14.7 vs 10.0 g), lateral root dry weight (3.7 vs 2.4 g), light-saturated photosynthesis (14.5 vs 10.1 μmol∙m-2∙s-1), maximum electron transport rate (119 vs 89 μmol∙m-2∙s-1), chlorophyll content (28.1 vs 12.9 g∙100g-1), leaf N content (27.5 vs 19.9 mg∙g-1), and fine root N content (26.1 vs 20.9 mg∙g-1), and a decrease in anthocyanin content (0.07 vs 0.16 ΔOD∙g-1). The path model indicated that an increase in the lateral root growth and fine root N content can lead to an increase in the leaf N content, in the N-deficient treatment. There were three separate paths that connected higher leaf N content to increased shoot biomass. These paths were mediated by the levels of anthocyanin, chlorophylls, and light-saturated photosynthesis rate (or rubisco capacity). The light-saturated photosynthesis model suggested that the increased uptake of N by fine roots in the tolerant cultivar was likely supported by the photosynthates translocated from the shoot to the root. Leaf N content was associated with multiple plant responses in the N-deficient treatment, and can be a useful screening trait for developing new cultivars, especially in marker-assisted molecular breeding

A Novel Method for Estimating Nitrogen Stress in Plants Using Smartphones

For profits in crop production, it is important to ensure that plants are not subjected to nitrogen stress (NS). Methods to detect NS in plants are either time-consuming (e.g., laboratory analysis) or require expensive equipment (e.g., a chlorophyll meter). In this study, a smartphone-based index was developed for detecting NS in plants. The index can be measured in real time by capturing images and processing them on a smartphone with network connectivity. The index is calculated as the ratio of blue reflectance to the combined reflectance of blue, green, and red wavelengths. Our results indicated that the index was specific to NS and decreased with increasing stress exposure in plants. Further, the index was related to photosynthesis based on the path analysis of several physiological traits. Our results further indicate that index decreased in the NS treatment due to increase in reflectance of red and green (or yellow) wavelengths, thus it is likely related to loss of chlorophyll in plants. The index response was further validated in strawberry and hydrangea plants, with contrasting plant architecture and N requirement than petunia

An illustration of ebb and flow fertigation system used to grow and impose nitrogen treatment to plants in the study.

See ‘Fertigation System’ in the Materials and Methods section for additional details on construction and components. (TIFF)</p

Differences in traits at cellular scale, including leaf nitrogen content (N_Leaf), stem nitrogen content (N_Stem), lateral root nitrogen content (N_LR), fine root nitrogen content (N_FR), anthocyanin content (ACN), carotenoid content (CTD), and total chlorophylls content (CHL), between sensitive and tolerant cultivars exposed to nitrogen deficient and optimal conditions.

Least square means followed by different letters are statistically different (P ≤ 0.05).</p

Path models showing relations among traits at cellular, leaf, and whole-plant scales in the nitrogen deficient treatment.

Refer to Tables 1–3 for trait names. Paths are separated using different colored arrows. Numbers adjacent to connecting arrows with an asterisk indicate slope of the relationship between two variables and statistical difference from zero (P ≤ 0.05). Error variance associated with predicting a variable is shown in boxes with letter ‘e’. The box colors were matched with different path models. A black dashed arrow indicates possible relationship not significant in the model. Dashed boxes [Rubisco and AOP (operating photosynthesis rate)] include possible connecting traits that were not measured in the study.</p

Traits at cellular, leaf, and whole-plant scales which were significantly different [increased (↑) or decreased (↓)] or non-significant between tolerant and sensitive cultivars in the N-deficient treatment.

Traits at cellular, leaf, and whole-plant scales which were significantly different [increased (↑) or decreased (↓)] or non-significant between tolerant and sensitive cultivars in the N-deficient treatment.</p

Representative poinsettia plants belonging to tolerant and sensitive cultivars grown in optimal and nitrogen deficient treatments.

Representative poinsettia plants belonging to tolerant and sensitive cultivars grown in optimal and nitrogen deficient treatments.</p

S1 Data -

Varieties that tolerate low nitrogen (N) application rates can reduce fertilizer costs, minimize nitrate leaching and runoff losses, and lower overall CO2 emissions associated with fertilizer manufacturing. The goal of our research is to show the usefulness of path models to identify key phenotypic traits for screening plants with a tolerance to low N application rates. We grew tolerant and sensitive cultivars of poinsettia (Euphorbia pulcherrima) using a water-soluble fertilizer (15-5-15 Cal Mag) in both optimal (electrical conductivity of 2.5 dS·m-1) and N-deficient (electrical conductivity of 0.75 dS·m-1) treatments and measured 24 different traits at the cellular, leaf, and whole-plant scales in both cultivars and treatments. The experiment was laid out as a split-plot design with N treatments as main plots and cultivars as sub-plots, with five replications. Path analysis was conducted to develop sequential relationships among these traits. Statistical comparisons between tolerant and sensitive cultivars in the N-deficient treatment indicated an increase in shoot biomass (19.9 vs 14.4 g), leaf area (2775 vs 1824 cm2), leaf dry weight (14.7 vs 10.0 g), lateral root dry weight (3.7 vs 2.4 g), light-saturated photosynthesis (14.5 vs 10.1 μmol∙m-2∙s-1), maximum electron transport rate (119 vs 89 μmol∙m-2∙s-1), chlorophyll content (28.1 vs 12.9 g∙100g-1), leaf N content (27.5 vs 19.9 mg∙g-1), and fine root N content (26.1 vs 20.9 mg∙g-1), and a decrease in anthocyanin content (0.07 vs 0.16 ΔOD∙g-1). The path model indicated that an increase in the lateral root growth and fine root N content can lead to an increase in the leaf N content, in the N-deficient treatment. There were three separate paths that connected higher leaf N content to increased shoot biomass. These paths were mediated by the levels of anthocyanin, chlorophylls, and light-saturated photosynthesis rate (or rubisco capacity). The light-saturated photosynthesis model suggested that the increased uptake of N by fine roots in the tolerant cultivar was likely supported by the photosynthates translocated from the shoot to the root. Leaf N content was associated with multiple plant responses in the N-deficient treatment, and can be a useful screening trait for developing new cultivars, especially in marker-assisted molecular breeding.</div

Photosynthesis (A) response to varying levels of intercellular carbon dioxide concentration (Ci) in tolerant and sensitive poinsettia cultivars grown in optimal and nitrogen deficient conditions.

Mean photosynthesis and standard error (n = 5) at each Ci level are shown.</p