Construction of an inducible system for the analysis of essential genes in Yersinia pestis.

Yersinia pestis, a Gram negative bacterium, causes bubonic and pneumonic plague. Emerging antibiotic resistance in clinical isolates is driving a need to develop novel antibiotics to treat infection by this transmissible and highly virulent pathogen. Proteins required for viability, so called essential genes, are attractive potential therapeutic targets, however, confirmation of essentiality is problematic. For the first time, we report the development of a system that allows the rapid determination of Y. pestis gene essentiality through mutagenesis and inducible expression of a plasmid borne copy of the target gene. Using this approach, we have confirmed the uridine monophosphate kinase PyrH as an essential protein in Y. pestis. This methodology and the tools we have developed will allow the confirmation of other putative essential genes in this dangerous pathogen, and facilitate the identification of novel targets for antimicrobial development.

Self-organized permeability in carbonate aquifers.

Advances over the past 40 years have resulted in a clear understanding of how dissolution processes in carbonate rocks enhance aquifer permeability. Laboratory experiments on dissolution rates of calcite and dolomite have established that there is a precipitous drop in dissolution rates as chemical equilibrium is approached. These results have been incorporated into numerical models, simulating the effects of dissolution over time and showing that it occurs along the entire length of pathways through carbonate aquifers. The pathways become enlarged and integrated over time, forming self-organized networks of channels that typically have apertures in the millimeter to centimeter range. The networks discharge at point-located springs. Recharge type is an important factor in determining channel size and distribution, resulting in a range of aquifer types, and this is well demonstrated by examples from England. Most carbonate aquifers have a large number of small channels, but in some cases large channels (i.e., enterable caves) can also develop. Rapid velocities found in ground water tracer tests, the high incidence of large-magnitude springs, and frequent microbial contamination of wells all support the model of self-organized channel development. A large majority of carbonate aquifers have such channel networks, where ground water velocities often exceed 100 m/d.

Modern freshwater microbialite analogues for ancient dendritic reef structures.

Microbialites are organosedimentary structures that can be constructed by a variety of metabolically distinct taxa. Consequently, microbialite structures abound in the fossil record, although the exact nature of the biogeochemical processes that produced them is often unknown. One such class of ancient calcareous structures, Epiphyton and Girvanella, appear in great abundance during the Early Cambrian. Together with Archeocyathids, stromatolites and thrombolites, they formed major Cambrian reef belts. To a large extent, Middle to Late Cambrian reefs are similar to Precambrian reefs, with the exception that the latter, including terminal Proterozoic reefs, do not contain Epiphyton or Girvanella. Here we report the discovery in Pavilion Lake, British Columbia, Canada, of a distinctive assemblage of freshwater calcite microbialites, some of which display microstructures similar to the fabrics displayed by Epiphyton and Girvanella. The morphologies of the modern microbialites vary with depth, and dendritic microstructures of the deep water (> 30 m) mounds indicate that they may be modern analogues for the ancient calcareous structures. These microbialites thus provide an opportunity to study the biogeochemical interactions that produce fabrics similar to those of some enigmatic Early Cambrian reef structures.

Physicians' recommendations for patients who undergo noncardiac surgery.

OBJECTIVE: To investigate how consulting physicians attempt to modify perioperative cardiac risk for patients who undergo noncardiac surgery by comparing the preoperative cardiac recommendations of consulting physicians in 2 university centres. DESIGN: Retrospective cross-sectional analysis. SETTING: Five hospitals affiliated with 2 Canadian universities. PATIENTS: Three hundred and eight preoperative consultations were evaluated in 297 patients who were 40 years of age or older and scheduled for noncardiac surgery. OUTCOME MEASURES: Cardiac drug recommendations at the preoperative consultation [corrected]; overall recommendations and practice variation between the 2 centres. RESULTS: The greatest changes in drug management suggested by consultants were the initiation of nitrates in 13% of the patients and a decrease in acetylsalicylic acid administration from 27% to 17%. Centre A physicians recommended adding an angiotensin-converting enzyme inhibitor 11% of the time, whereas centre B physicians recommended such an inhibitor in only 1% of the patients (p = 0.001). In patients taking acetylsalicylic acid at the preoperative consultation, Centres A and B physicians recommended withholding the drug 47% and 22% of the time, respectively (p = 0.03). These differences persisted between the 2 centres after controlling for physician estimates of risk. CONCLUSIONS: Consultants frequently recommended perioperative changes in the use of cardiac medications, and there were differences in practice patterns between the 2 centres. These differences may be affecting patient outcomes and highlight the need for randomized clinical trials to determine the impact of perioperative drug administration on bleeding, myocardial infarction and death.

Physician estimates of perioperative cardiac risk in patients undergoing noncardiac surgery.

BACKGROUND: We know little about how physicians assess perioperative cardiac risk in patients undergoing noncardiac surgery. OBJECTIVES: To evaluate preoperative medical consultations and determine the extent to which consultants used validated cardiac risk indices and specialized noninvasive cardiac tests, and to assess agreement between physician ratings of cardiac risk (low, moderate, or high) and risk estimates derived using validated cardiac risk indices or, in the case of vascular surgery, a risk index. METHODS: This observational study was conducted at 5 Canadian teaching hospitals affiliated with 2 universities. We retrospectively evaluated 308 preoperative consultations performed in 297 patients and examined the frequency with which consultants recorded the use of validated cardiac risk indices. We used K statistics to quantify the extent to which physician ratings of cardiac risk agreed with risk estimates derived using validated cardiac risk indices. RESULTS: Physicians recorded use of a risk index in 31% of the consultations, but the index used was almost always the suboptimal classification of the American Society of Anesthesiologists. The agreement between physician estimates of cardiac risk and the validated cardiac risk indices was only fair, with a weighted K of 0.38 (95% confidence interval, 0.28-0.49). Overestimation and underestimation of cardiac risk occurred in 16% and 13% of the consultations, respectively. Consultants did not order dipyridamole thallium imaging or dobutamine stress echocardiography for any moderate-risk patients undergoing vascular surgery. CONCLUSIONS: Physicians underuse validated cardiac risk indices, and the agreement between the cardiac risk estimates and risk as determined by validated cardiac indices is suboptimal. Physicians are also underusing dipyridamole thallium imaging and dobutamine stress echocardiography for moderate-risk patients undergoing vascular surgery.

A simple treatment of post-lumbar-puncture headache.

We report a case of post-lumbar-puncture headache successfully treated with intravenous caffeine sodium benzoate. The patient presented to the emergency department with a severe headache three days after a myelogram of the lumbar region. Caffeine sodium benzoate (500 mg) in 1 liter of fluid (D5LR) intravenously over one and a half hours was administered. The patient reported complete resolution of symptoms and no recurrence of headache. Caffeine sodium benzoate is a simple treatment of post-lumbar-puncture headaches. It should be considered as a safe alternative to an epidural blood patch for the treatment of post-lumbar-puncture headaches.

The effect of activated charcoal on N-acetylcysteine absorption in normal subjects.

The discovery of the effectiveness of oral antidotes such as N-acetylcysteine (NAC) for acetaminophen poisonings has raised questions about the appropriateness of concomitant administration with activated charcoal. A number of studies have attempted to clarify this question without complete success. This study was designed to evaluate the difference in serum levels of NAC when given with activated charcoal. Nineteen patients completed a two-phase cross-over study in which they served as their own controls. Each subject in phase 1 received 140 mg/kg of diluted, chilled NAC orally, and venous blood samples were drawn for analysis. Phase 2 consisted of a 100-g dose of activated charcoal followed by NAC. Samples were transported immediately and assayed using spectrophotometry. A reduction in peak NAC level of 29% (P less than .02) and a reduction of total area under the curve (AUC) of 39% (P less than .001) was noted. Although it may be preferable to avoid completely the use of activated charcoal when using NAC to treat overdoses of acetaminophen, we recommend that if these agents are used together, doses of NAC be increased by 40% to compensate for the decreased oral absorption of NAC.

Sea-level lowering during the illinoian glaciation: evidence from a bahama "blue hole".

Stalagmites have been recovered from 45 meters below sea level in an underwater karstic cave ("blue hole") near Andros Island in the Bahamas. Uranium series ages, corrected for contamination of the sample by young marine carbonate replacements, show that the speleothem was deposited between 160,000 and 139,000 years before the present. This period corresponds to the Illinoian glacial event and demonstrates that sea level must have been lowered by at least 42 meters (allowing for subsidence) from its present position during this time.

Continental pleistocene climatic variations from speleothem age and isotopic data.

Speleothems from continental North American caves have been dated by means of the (230)Th/(234)U method. Oxygen isotopic variations in the dated samples and phases of speleothem deposition can be interpreted in terms of climatic change. A glacial chronology constructed from the age and isotopic data lends support to the astronomical theory of climatic change.