Molecular epidemiology of infections caused by methicillin-resistant staphylococci

The review deals with the periodicity of the spread of methicillin-resistant S. aureus (MRSA) strains during the last 40 years, the mechanism of their resistance to methicillin and other beta-lactamic antibiotics, the genetic control of methicillin resistance, the genome organization of mec DNA and its possible cause, as well as the organization of epidemiological surveillance on MSRA in hospitals. The problem of changes in the epidemiology of staphylococcal infections due to the appearance of MRSA in the absence of contacts with carriers, treatment with antibiotics or stay in a hospital is discussed. The concern of public health authorities in connection with the emergence of MRSA strains, moderately resistant or resistant to vancomycin, is also discussed. The most promising programs of the MRSA study, as well as the optimum programs introduced in economically developed counties for the control of hospital infections caused by MRSA, are considered.     

Mutagenesis by transient misalignment

Based upon a consideration of two mutational hot spots produced during DNA synthesis by a eukaryotic DNA repair polymerase, we suggested that certain base substitution errors result not from direct miscoding but from correct coding by a transiently misaligned template-primer (Kunkel, T. A., and Alexander, P. S. (1986) J. Biol. Chem. 261, 160-166). This model, which we called dislocation mutagenesis, has been directly tested. Introducing a single, phenotypically silent G----A base change into the template switches the base substitution specificity at the immediately adjacent hot spot, a T residue, from T----G transversions to T----A transversions. The cumulative change in frequency, represented by the disappearance of the T----G events and the appearance of the T----A events, is greater than 300-fold. These data demonstrate that during DNA synthesis in vitro, a base at one position can code a mutation at another position. This mechanism can operate over greater distances to produce complex mutations as well. We present one example in which a 123-base deletion containing three base changes at one end of the deletion can be precisely explained by transient misalignment. It remains to be established whether mutagenesis by dislocation operates in vivo to produce biologically significant changes in genetic information.     

Predicting and correcting bias caused by measurement error in line transect sampling using multiplicative error models

Line transect sampling is one of the most widely used methods for animal abundance assessment. Standard estimation methods assume certain detection on the transect, no animal movement, and no measurement errors. Failure of the assumptions can cause substantial bias. In this work, the effect of error measurement on line transect estimators is investigated. Based on considerations of the process generating the errors, a multiplicative error model is presented and a simple way of correcting estimates based on knowledge of the error distribution is proposed. Using beta models for the error distribution, the effect of errors and of the proposed correction is assessed by simulation. Adequate confidence intervals for the corrected estimates are obtained using a bootstrap variance estimate for the correction and the delta method. As noted by Chen (1998, Biometrics 54, 899-908), even unbiased estimators of the distances might lead to biased density estimators, depending on the actual error distribution. In contrast with the findings of Chen, who used an additive model, unbiased estimation of distances, given a multiplicative model, lead to overestimation of density. Some error distributions result in observed distance distributions that make efficient estimation impossible, by removing the shoulder present in the original detection function. This indicates the need to improve field methods to reduce measurement error. An application of the new methods to a real data set is presented.     

Measurement error in heat tolerance assays

Biological measurements inherently involve some measurement error (ME), which is a major concern because measurement accuracy (how closely a measurement reproduces the true value of the attribute being measured) and statistical power steadily decrease with increasing ME. However, ME has been largely overlooked in the thermal biology literature, which can be explained by the fact that thermotolerance estimates often involve the collapse or death of the tested individuals and measurements cannot be repeated in vivo with the same specimen under identical conditions. Here we assess inter- and intra-researcher (test-retest) reliability of heat tolerance measured as knockdown time from digital recordings of Drosophila subobscura flies individually assayed in vials with a dynamic method. We provide a summary of various estimators used to compute measurement reliability (the degree to which the measurement is affected by ME) together with their statistical properties. Our results indicate that the estimation of heat knockdown time has poor reliability: intra-researcher ME=29% and inter-researcher ME=34%. This difference is attributed to lack of ‘accurateness’ (the difference in the marginal distributions of the measurements taken by the two researchers) because measurement imprecision was essentially the same in both estimates (27%). In view of our results we conclude that thermal biologists should report the reliability of thermotolerance estimates and, when necessary, adopt some straightforward guidelines suggested here to improve measurement reliability.     

Changing spatial epidemiology of pertussis in continental USA

Prediction and control of the geographical spread of emerging pathogens has become a central public health issue. Because these infectious diseases are by definition novel, there are few data to characterize their dynamics. One possible solution to this problem is to apply lessons learnt from analyses of historical data on familiar and epidemiologically similar pathogens. However, the portability of the spatial ecology of an infectious disease in a different epoch to other infections remains unexamined. Here, we study this issue by taking advantage of the recent re-emergence of pertussis in the United States to compare its spatial transmission dynamics throughout the 1950s with the past decade. We report 4-year waves, sweeping across the continent in the 1950s. These waves are shown to emanate from highly synchronous foci in the northwest and northeast coasts. In contrast, the recent resurgence of the disease is characterized by 5.5-year epidemics with no particular spatial structure. We interpret this to be the result of dramatic changes in patterns of human movement over the second half of the last century, together with changing age distribution of pertussis. We conclude that extrapolation regarding the spatial spread of contemporaneous pathogens based on analyses of historical incidence may be potentially very misleading.     

Methods of molecular epidemiology of infections caused by group B streptococci

In this review the comparative analysis of advantages and disadvantages of the known methods for the immunological diagnostics of streptococcal infections (serotyping, phage typing), as well as the methods of molecular epidemiology (PCR typing with the use of "disseminated" priming, ribotyping, electrophoresis in the pulsing electric field, etc.), is presented. Essentially new approaches, capable of being used in future for the control of epidemically topical clones of group B streptococci, are discussed.     

Measurement error in racial and ethnic statistics

In the United States, the racial and ethnic statistics published by the National Center for Health Statistics (NCHS) assume that each member of the U.S. population has a race and ethnicity and that if a member is black or white with respect to his risk of one disease, he is the same race with respect to his risk of another. Such an assumption is mistaken. Race and ethnicity are taken by the NCHS to be an intrinsic property of members of a population, when they should be taken to depend on interest. The actual or underlying race or ethnicity of members of a population depends on the risk whose variation within the population we wish to describe or explain.

The epidemiology of the infection caused by the human immunodeficiency virus in the USSR

The existing system of the epidemiological surveillance of HIV infection in the USSR makes it possible to evaluate the present situation as the beginning of epidemic. The main routes of the transfer of HIV infection as per data for April 1989: 50% by the sexual route, 25.8% by parenteral manipulations.     

Evaluation of time-to-pregnancy as a measure in environmental epidemiology

Since the late 80's, time to pregnancy has been used in environmental epidemiology to explore adverse effects of different exposures. The advantages of this measure and additional elements to be considered in the performance of this type of studies are reviewed. Study design includes the following steps: population selection, sample size, outcome measurement, statistical analyses and sources of bias. Guidelines were suggested for the properly development of this type of study.     

Measurement of non-randomness in spatial distributions

The measurement of departure from randomness in spatial distributions has widespread application in ecological work. Several “indices of non-randomness” are compared with regard to their dependence on sample number, sample size and density. Criteria for the best choice of index for specific situations are discussed. A new coefficient C_x is proposed for use with positively contagious distributions and tests of significance are given. When C_x and another index (S²/m−1) are used for positive and negative contagion respectively, values ranging from −1 through 0 (random) to +1 are obtained, regardless of sample number, sample size or density.     

植物对环境应力刺激的生物学效应

植物生长在自然环境中由于其“不动性”而不可避免地要受到各种环境应力的刺激,应力－生长关系一直是生物学家和物理学家所关心的课题,是生物力学的灵魂。很多研究已经表明外界应力作用对植物的生长发育有着重要的影响。本综述了国内外关于应力对植物组织所引起的生物学效应,首先论述了环境应力所引起的宏观生物学效应,随后重点论述了环境应力所引起的生物学效应在细胞和分子水平上的研究,其中包括单个细胞的加载、电磁场、微     

Novel method for chase analysis of oligosaccharide metabolic error caused by xenobiotics

Saccharide primers, such as dodecyl β-lactoside (Lac-C12), are unique artificial precursors of glycolipid synthesis. In culture media supplemented with saccharide primers, they are taken up by the cells in the culture media and glycosylated by cellular glycosyltransferases in the Golgi apparatus to form pseudo-glycolipids. In this study, we examine the effects of various xenobiotics on glycolipid synthesis by implementing a novel method to analyze pseudo-glycolipids, mainly gangliosides, produced by ONS-76 medulloblastoma cells in a culture medium containing various xenobiotics. The ganglioside group of pseudo-glycolipids was effectively purified by using strong anion-exchange cartridges. The production of pseudo-gangliosides was stimulated by N-(n-butyl)deoxygalactonojirimycin (NB-DGJ), but was inhibited by castanospermine, 2-deoxy-2-fluoro-d-galactose, tunicamycin, and brefeldin A. Because the cells in the culture medium are exposed to the saccharide primers and xenobiotics at the same time, and are secreted in the culture medium in their glycosylated form, our method can be used to effectively analyze the direct effects of xenobiotics on ganglioside synthesis.     

Improving xylem hydraulic conductivity measurements by correcting the error caused by passive water uptake

Xylem hydraulic conductivity (K) is typically defined as K = F/(P/L), where F is the flow rate through a xylem segment associated with an applied pressure gradient (P/L) along the segment. This definition assumes a linear flow-pressure relationship with a flow intercept (F(0) ) of zero. While linearity is typically the case, there is often a non-zero F(0) that persists in the absence of leaks or evaporation and is caused by passive uptake of water by the sample. In this study, we determined the consequences of failing to account for non-zero F(0) for both K measurements and the use of K to estimate the vulnerability to xylem cavitation. We generated vulnerability curves for olive root samples (Olea europaea) by the centrifuge technique, measuring a maximally accurate reference K(ref) as the slope of a four-point F vs P/L relationship. The K(ref) was compared with three more rapid ways of estimating K. When F(0) was assumed to be zero, K was significantly under-estimated (average of -81.4 ± 4.7%), especially when K(ref) was low. Vulnerability curves derived from these under-estimated K values overestimated the vulnerability to cavitation. When non-zero F(0) was taken into account, whether it was measured or estimated, more accurate K values (relative to K(ref) ) were obtained, and vulnerability curves indicated greater resistance to cavitation. We recommend accounting for non-zero F(0) for obtaining accurate estimates of K and cavitation resistance in hydraulic studies.     

干旱荒漠绿洲景观空间格局及其受水资源条件的影响分析

以黑河流域下游额济纳荒漠绿洲为研究对象,分析了景观生态的基本特点和景观嵌块体类型,通过景观空间格局及其变化分析与景观生态功效的评价,利用８０年代和９０年代两期有关景观生态的资料,论述了水资源条件变化对研究区景观格局的影响,指出河流廓道是干旱区荒漠绿洲的主要生态流,河流廓道的变化是导致荒漠绿洲景观格局变化的驱动力。     

Synchrony of spatial populations induced by colored environmental noise and dispersal

Spatial synchrony of oscillating populations has been observed in many ecological systems, and its influences and causes have attracted the interest of ecologists. Spatially correlated environmental noises, dispersal, and trophic interactions have been considered as the causes of spatial synchrony. In this study, we develop a spatially structured population model, which is described by coupled-map lattices and incorporates both dispersal and colored environmental noise. A method for generating time series with desired spatial correlation and color is introduced. Then, we use these generated time series to analyze the influence of noise color on synchrony in population dynamics. The noise color refers to the temporal correlation in the time series data of the noise, and is expressed as the degree of (first-order) autocorrelation for autoregressive noise. Patterns of spatial synchrony are considered for stable, periodic and chaotic population dynamics. Numerical simulations verify that environmental noise color has a major influence on the level of synchrony, which depends strongly on how noise is introduced into the model. Furthermore, the influence of noise color also depends on patterns of dispersal between local populations. In addition, the desynchronizing effect of reddened noise is always weaker than that of white noise. From our results, we notice that the role of reddened environmental noise on spatial synchrony should be treated carefully and cautiously, especially for the spatially structured populations linked by dispersal.     

Two-dimensional spatial error distribution of key tensiomyographic parameters

Tensiomyography detects the contraction time (Tc) and amplitude (Dm) of muscle belly thickening during maximal isometric twitch contraction. The assessment of both parameters is highly reliable; however, it seems that their calculation depends on the measurement point. The aim of the study was to determine spatial relative error distribution of Tc and/or Dm within a two-dimensional array of 27 (3 × 9) measurement points in comparison to the reference point (RP) in 12 male participants (22.5 ± 3.1 years). The RPs were determined as follows: in the biceps brachii (BB) at 50% of the humerus length; in the erector spinae (ES) at the height of the iliac crest; in the vastus lateralis (VL), vastus medalis (VM), and rectus femoris (RF) at 30%, 20%, and 50% of femur length above the patella, respectively. The surface area under the 3% relative error in Dm (BB: 4.0; VL: 3.8; VM; 8.2; RF: 6.2; ES: 2.4 cm²) was lower than in Tc (BB: 6.9; VL: 3.8; VM; 4.6; RF: 9.5; ES: 3.7 cm²), yielding merged values (BB: 3.9; VL: 3.7; VM; 4.8; RF: 5.1; ES: 2.4 cm²). Dm show twice as steep relative error rate when moving away from the RP in comparison to Tc, which seems to be less sensitive to spatial sensor positioning.