1279. Risk Factors for Colistin Resistance Among Carbapenem-Resistant Klebsiella pneumoniae (CRKP) in a Network of Long-term Acute Care Hospitals (LTACHs)

Background Colistin resistance in CRKP presents a serious clinical challenge for patients of LTACHs. However, risk factors for colistin-resistant CRKP have not been previously characterized in this population. Here, we determined risk factors for colistin resistance among CRKP isolates from a network of LTACHs. Methods CRKP clinical cultures were collected from 21 Kindred Healthcare LTACHs in 4 US states (California, Texas, Florida, Kentucky) from 8/1/14-7/25/15. Cultures collected within 30 days of a prior CRKP culture from the same patient were excluded. Colistin resistance (minimum inhibitory concentration ≥4) was determined using a custom SensititreTM broth microdilution assay (ThermoFisher Scientific, Waltham, MA). Multivariate logistic regression was performed to evaluate candidate risk factors of age, sex, cirrhosis, chronic kidney disease, culture source, length of stay, indwelling line or tracheostomy, and antibiotic exposure (colistin, fluoroquinolones, 3rd-5th generation cephalosporins, piperacillin-tazobactam, carbapenems, and aminoglycosides) for ≥48 hours in the prior 30 days. Results Among 430 CRKP cultures (237 respiratory, 145 urine, 38 blood, 10 wound) from 375 patients, 144 (33.5%) were colistin-resistant. In multivariate analysis, colistin resistance was associated with prior colistin exposure (odds ratio [OR] = 5.9, 95% CI = 2.5-14.0) and culture source (Wald test for joint significance, p=0.03), with higher odds of colistin resistance among respiratory (OR = 2.9, 95% CI = 1.2-7.2), urine (OR = 1.6, 95% CI = 0.7-4.1), or wound (OR = 2.2, 95% CI = 0.4-11.5) compared to blood cultures. Conclusion In this sample of CRKP from LTACHs, colistin resistance was associated with prior colistin exposure and respiratory culture source. Other patient factors such as co-morbidities, indwelling devices or tracheostomy, or exposure to other antibiotics/antibiotic classes were not associated with colistin resistance in CRKP. These findings will help inform strategies to reduce colistin resistance and identify LTACH patients at risk of colistin-resistant CRKP. Disclosures Jennifer Han, MD, MSCE, GlaxoSmithKline (Employee, Shareholder) Ebbing Lautenbach, MD, MPH, MSCE, Merck (Other Financial or Material Support, Member of Data and Safety Monitoring Board (DSMB))

Anti‐malarial drug effects on parasite dynamics in vivax malaria

Relapses of Plasmodium vivax malaria are prevented by 8-aminoquinolines. If hypnozoites survive, then the subsequent blood stage infections in early relapses (< 2 months) are suppressed by the slowly eliminated anti-malarial drugs used to treat the blood stage infection (chloroquine, artemisinin combination treatments), but they are not usually eliminated. The 8-aminoquinolines have significant blood stage activity which contributes to therapeutic responses. The latent interval from primary infection to early relapse depends on the number of activatable hypnozoites, the dose of anti-malarial, its pharmacokinetic properties, the level of resistance (minimum inhibitory concentration) and immunity. The dose–response relationship for radical curative efficacy of primaquine and tafenoquine is steep over the total dose range from 1.5 to 5 mg base/kg which may explain the poor efficacy of tafenoquine at the currently recommended dose.

Magnetoresistance of Bi2Se3 Whiskers at Low Temperatures

Temperature dependencies of Bi2Se3 whiskers’ resistance with Pd doping concentration of 1´1019 cm-3 where measured in temperature range 4.2 - 300 K. At temperature 5.3 K a sharp drop in the whisker resistance was found. The observed effect is likely connected with contribution of two processes such as the electron localization in the whiskers and transition in superconducting state at temperature 5.3 K, which is likely result from Pd complexes.Transversemagnetoresistance in n-type Bi2Se3 whiskers with Pd doping concentration in the vicinity to themetal-insulator transition (MIT) from metal side of the transition were studied in magnetic field 0 -10 T. For the whiskers a resistance minimum was observed at temperature about 25 K that is connected with Kondo effect.

Resistivity minima in the disordered cluster glass intermetallic compound Dy5Pd2: influence of quantum interference effects

A resistance minimum in the temperature dependence of Dy5Pd2 has been interpreted in terms of contributions from magnetic and phonon scattering, electron–electron interactions and weak localization.

Research on Integration of Urban and Rural Bus Line Network Planning Model

The advance of urbanization makes existing bus line network can not meet the travel needs of the increasing urban and rural residents, but reasonable integration of urban and rural bus line network planning is able to effectively solve this problem. In this paper, as a starting point to establish bi-level programming model of integration of urban and rural bus line network planning, the goal of upper model is minimum total investment in the construction of urban and rural public bus line network to the transport sector and the target of lower model is network resistance minimum. Then, based on the genetic algorithm to solve the model and put forward steps and flowchart. Established bi-level programming model by analyzing the studies can provide a theoretical reference for the planning of urban and rural bus line network.