Transmission of methicillin-resistant Staphylococcus aureus infection through solid organ transplantation: confirmation via whole genome sequencing.

We describe two cases of donor-derived methicillin-resistant Staphylococcus aureus (MRSA) bacteremia that developed after transplantation of organs from a common donor who died from acute MRSA endocarditis. Both recipients developed recurrent MRSA infection despite appropriate antibiotic therapy, and required prolonged hospitalization and hospital readmission. Comparison of S. aureus whole genome sequence of DNA extracted from fixed donor tissue and recipients' isolates confirmed donor-derived transmission. Current guidelines emphasize the risk posed by donors with bacteremia from multidrug-resistant organisms. This investigation suggests that, particularly in the setting of donor endocarditis, even a standard course of prophylactic antibiotics may not be sufficient to prevent donor-derived infection.

Salmonella in dairy operations in the United States: prevalence and antimicrobial drug susceptibility.

Salmonella serotypes are important foodborne pathogens of humans that can be acquired through consumption of contaminated meat and dairy products. Salmonella infection also can be a significant animal health issue. As part of a national study of U.S. dairy operations conducted between March and September 2002, fecal samples were collected from representative cows in 97 dairy herds in 21 states and were cultured to determine the prevalence of Salmonella shedding. Salmonella was recovered from the feces of at least one cow in 30.9% of the herds. Overall, 7.3% of fecal samples were culture positive for Salmonella. The three most frequently recovered serotypes were Salmonella Meleagridis (24.1%), Salmonella Montevideo (11.9%), and Salmonella Typhimurium (9.9%). The susceptibilities of Salmonella isolates recovered were determined using a panel of 16 antimicrobial drugs. Salmonella isolates recovered from dairy cows had relatively little resistance to these antimicrobial agents; 83.0% of the isolates were susceptible to all antimicrobials tested. This study provides updated information on the prevalence and susceptibility patterns of Salmonella in dairy herds and on cow and herd characteristics. These data contribute to our understanding of the ecology of Salmonella in the dairy farm environment.

Targeted disruption of the Ceacam1 (MHVR) gene leads to reduced susceptibility of mice to mouse hepatitis virus infection.

The CEACAM1 glycoproteins (formerly called biliary glycoproteins; BGP, C-CAM, CD66a, or MHVR) are members of the carcinoembryonic antigen family of cell adhesion molecules. In the mouse, splice variants of CEACAM1 have either two or four immunoglobulin (Ig) domains linked through a transmembrane domain to either a short or a long cytoplasmic tail. CEACAM1 has cell adhesion activity and acts as a signaling molecule, and long-tail isoforms inhibit the growth of colon and prostate tumor cells in rodents. CEACAM1 isoforms serve as receptors for several viral and bacterial pathogens, including the murine coronavirus mouse hepatitis virus (MHV) and Haemophilus influenzae, Neisseria gonorrhoeae, and Neisseria meningitidis in humans. To elucidate the mechanisms responsible for the many biological activities of CEACAM1, we modified the expression of the mouse Ceacam1 gene in vivo. Manipulation of the Ceacam1 gene in mouse embryonic stem cells that contained the Ceacam1a allele yielded a partial knockout. We obtained one line of mice in which the insert in the Ceacam1a gene had sustained a recombination event. This resulted in the markedly reduced expression of the two CEACAM1a isoforms with four Ig domains, whereas the expression of the two isoforms with two Ig domains was doubled relative to that in wild-type BALB/c (+/+) mice. Homozygous (p/p) Ceacam1a-targeted mice (Ceacam1aDelta4D) had no gross tissue abnormalities and were viable and fertile; however, they were more resistant to MHV A59 infection and death than normal (+/+) mice. Following intranasal inoculation with MHV A59, p/p mice developed markedly fewer and smaller lesions in the liver than +/+ or heterozygous (+/p) mice. The titers of virus produced in the livers were 50- to 100-fold lower in p/p mice than in +/p or +/+ mice. p/p mice survived a dose 100-fold higher than the lethal dose of virus for +/+ mice. +/p mice were intermediate between +/+ and p/p mice in susceptibility to liver damage, virus growth in liver, and susceptibility to killing by MHV. Ceacam1a-targeted mice provide a new model to study the effects of modulation of receptor expression on susceptibility to MHV infection in vivo.

B-cell-mediated lysis of cells infected with the neurotropic JHM strain of mouse hepatitis virus.

Cells expressing the spike (S) glycoprotein of the neurotropic JHM strain (JHMV) of mouse hepatitis virus (MHV) are susceptible to lysis by B cells derived from naïve mice, including B cells from perforin-deficient mice. Cytolysis requires interaction of the virus receptor and the viral S glycoprotein, is independent of other viral-induced components, and is not a unique property of B cells. Neutralizing anti-S-protein monoclonal antibodies (mAb) and a mAb specific for the viral receptor inhibit lysis. However, cells infected with an MHV strain unable to induce cell-cell fusion are resistant to lysis and lysis of JHMV-infected cells is inhibited by an anti-S-protein nonneutralizing mAb which prevents S-protein-mediated cell fusion. These data suggest that B cells may function as antibody-independent innate immune response during JHMV infection in vivo.

Human coronavirus 229E infects polarized airway epithelia from the apical surface.

Gene transfer to differentiated airway epithelia with existing viral vectors is very inefficient when they are applied to the apical surface. This largely reflects the polarized distribution of receptors on the basolateral surface. To identify new receptor-ligand interactions that might be used to redirect vectors to the apical surface, we investigated the process of infection of airway epithelial cells by human coronavirus 229E (HCoV-229E), a common cause of respiratory tract infections. Using immunohistochemistry, we found the receptor for HCoV-229E (CD13 or aminopeptidase N) localized mainly to the apical surface of airway epithelia. When HCoV-229E was applied to the apical or basolateral surface of well-differentiated primary cultures of human airway epithelia, infection primarily occurred from the apical side. Similar results were noted when the virus was applied to cultured human tracheal explants. Newly synthesized virions were released mainly to the apical side. Thus, HCoV-229E preferentially infects human airway epithelia from the apical surface. The spike glycoprotein that mediates HCoV-229E binding and fusion to CD13 is a candidate for pseudotyping retroviral envelopes or modifying other viral vectors.

A dynamic analysis of turnover in employment and child care.

The causes of turnover in child-care arrangements and maternal employment are analyzed using panel data from the National Longitudinal Survey of Youth, supplemented with state-level information on child-care markets. The results indicate that turnover in child care is quite high and that child and family characteristics help explain turnover. Important factors include the mother's wage, the cost of child care, age of the child, and previous child-care decisions. The reduced-form nature of the analysis makes it difficult to determine whether these factors are important because they are associated with unstable child-care supply or because they affect family decisions, conditional on supply factors. The results provide no direct evidence that child-care turnover is higher in states with more unstable child-care markets.

Adaptation of measles virus to polarized epithelial cells: alterations in virus entry and release.

We have previously shown that the Edmonston strain of measles virus enters and is released preferentially at the apical surfaces of polarized epithelial cells. Small amounts of virus were found to be released at the basal surface. In the present study, we passaged the virus in polarized cells and characterized the passaged virus for its pattern of entry and release in epithelial cells as well as the ability to downregulate the receptor CD46. In contrast to the original stock virus, the passaged virus was found to be released at close to the same levels from both the apical and the basal surfaces. Accumulation of viral nucleocapsids and virus budding were observed at both membrane surfaces when cells were infected with the passaged virus. The passaged virus was also found to enter efficiently at the basal surface, unlike the original stock virus. Syncytial formation was observed at earlier times postinfection in cells infected with the passaged virus compared to cells infected with the stock virus. On Caco-2 cells, CD46 is found on both surfaces but is preferentially expressed on the apical membrane. The original Edmonston stock and two other wild-type strains, Chicago and Davis, were found to downregulate CD46 levels on the apical but not on the basolateral membrane of Caco-2 cells, while the passaged Edmonston measles virus did not downregulate CD46 on either surface. These data indicate that passage of measles virus through polarized epithelial cells results in selection of virus which exhibits a bidirectional pattern of entry and release through both the apical and the basolateral surface and which no longer downregulates CD46 expression on the cell surface.

Entry and release of measles virus are polarized in epithelial cells.

The initial site of virus replication during measles infection is in the epithelial cells of the respiratory tract. We have investigated measles virus infection of two types of polarized epithelial cells to determine if entry and/or release of the virus is confined to either the apical or the basolateral plasma membrane. The Caco-2 line of human intestinal epithelial cells and the polarized Vero C1008 monkey kidney cell line were grown on permeable supports and inoculated either through the apical or basolateral surfaces. Cells exposed to virus in the apical medium showed high levels of synthesis of virus-specific proteins, whereas no synthesis of viral proteins was detected in cells inoculated at the basolateral surface. Virus titers derived from apically infected cells were found to be about 1000-fold greater than titers derived from cells infected at the basolateral surface. Indirect immunofluorescence results also demonstrated that expression of measles viral antigens occurs at high levels only when input virions are inoculated at the apical surface. To investigate the localization of CD46 and moesin, which are receptors for measles virus, Caco-2 cells were incubated with monoclonal antibodies against CD46 or moesin followed by 125I-labeled anti-mouse Ig. The results indicate that CD46 is expressed preferentially on the apical membranes while moesin appears to be present at similar levels on both surfaces. Release of the virus was also examined and found to be polarized as well. Virus was released into the apical medium at up to 1000-fold higher titers than virus released into the basolateral medium. These results demonstrate that in two epithelial cell types measles virus preferentially enters and is released from epithelial cells in a polarized fashion through the apical plasma membrane.

Labor force dynamics of older men.

"This paper describes and analyzes movements of older men among labor force states [in the United States] using quarterly observations derived from the Retirement History Survey (RHS)." The results indicate "substantial undercounts in the biannual data, indicating that the prevalence of labor force movements at older ages has been underestimated previously.... The results show that labor force dynamics at older ages are important, including duration and spell occurrence dependence, and work experience effects. These effects are robust to nonparametric controls for unobserved heterogeneity. The estimates indicate that social security benefits have strong effects on the timing of labor force transitions at older ages, but that changes in social security benefit levels over time have not contributed much to the trend toward earlier labor force exit."

Child care demand and labor supply of young mothers over time.

This paper uses panel data from the National Longitudinal Survey of Youth (NLSY) to analyze jointly fertility, employment, and child care decisions of young women over time. As these young women age (from 21 to 25 years on average) they become increasingly likely to have young children, to be employed, and to use non-relative forms of child care. A multivariate analysis reveals that rising wage rates and changes in household structure are important determinants of these upward trends. Further analysis reveals a considerable amount of movement each year among states defined by the presence of young children, employment, and child care arrangement. Overall the young women in the NLSY can be characterized as being in a volatile stage of their lives, when many economic and demographic factors are changing. They appear to respond to these changes by altering their labor supply and child care behavior.

Fertility, employment, and child-care costs.

A sample of labor-market and birth histories is used to estimate the effects of child-care costs on employment and fertility decisions. A reduced-form empirical analysis is performed, which is based on hazard functions for transitions among various fertility--employment states. Higher child-care costs result in a lower birth rate for nonemployed women but not for employed women. Higher child-care costs also lead to an increase in the rate of leaving employment and a reduction in the rate of entering employment. The results suggest that potential behavioral effects of child-care subsidies could be significant and should be taken into account when alternative child-care policies are being debated.

Fertility, child nutrition, and child mortality in Nicaragua: an economic analysis of interrelationships.

PIP: The results of an investigation into the relationships among child nutrition, child mortality, and fertility in Nicaragua are presented. Data are from a 1977-1978 survey of 1,085 households. The analysis is performed using a consistent model developed from the household production model of Gary S. Becker. The focus of the study is on the identification of key variables that can hasten simultaneously the decline of fertility and mortality and the improvement of child nutrition in developing countries. In the urban sector, the woman's potential wage rate had the largest impact on improving child nutrition and lowering fertility; educational status of both partners was also significant. In rural areas, other family income and female education were the significant variables positively affecting child nutrition and reducing fertility.^ieng

Plate assay for determining the time of production of protease, cellulase, and pectinases by germinating fungal spores.

A new method for detecting enzymes produced by fungal spores during germination is described here. With this method, the production of enzymes such as protease, cellulase, or pectinase can be correlated with the extent of spore germination. Germination is studied in vitro on agar-based media containing protein, cellulose, or pectin. The spores are immobilized on a permeable membrane mounted on the substrate-containing medium. At various times after inoculation the membrane-bound spores are removed and the medium is stained. The extent of germination is assessed by microscopic examination of the spores and the presence of active hydrolytic enzymes is revealed by the staining. The staining methods are sensitive; detection limits are 1 X 10(-3) unit of cellulase; 2 X 10(-4) unit of protease; 3 X 10(-3) unit of pectin lyase; 3.5 units of polygalacturonase; 2 X 10(-3) unit of pectin methyl esterase. The method has been demonstrated by studying the production of enzymes by germinating conidia of Botrytis cinerea. Cellulase and protease were present before any spores germinated. Pectin lyase was first observed when at least 80% of the spores had germinated. Pectin methyl esterase and polygalacturonase were not produced by the spores.

A model of child nutrition, fertility, and women's time allocation: the case of Nicaragua.

"This study had two main goals. The first was to test the hypothesis that women who work in the informal sector of the labor force have better-nourished children, ceteris paribus, than women who work in the formal sector. A simple home production model for child nutrition incorporating this hypothesis was specified and the behavior of a utility-maximizing household investigated. The empirical estimates of the nutritional status production function provided no convincing support for the hypothesis." The second goal was "to investigate the joint determinants of child nutrition and of women's fertility and work choices....[It is suggested] that increases in women's education and formal sector wages will induce declines in fertility and improvements in child nutrition. Increases in informal sector wages will improve nutrition but have little impact on fertility, and income effects are minimal on all three variables." Data are from a household survey conducted in Nicaragua in 1977 and 1978.

The impact of demographic changes on income distribution in a developing country.

"A common hypothesis regarding the distribution of income is that it tends to become more unequal in the initial and middle stages of economic development, in part because of demographic changes. However, previous studies of the effect of demographic changes on income distribution are not based on the underlying micro determinants of the income components." In the present paper, "the micro determinants of the probability of receipt and amount received conditional on receipt of four income components are estimated for three regions defined by the degree of urbanization. Five simulations of hypothetical demographic changes are conducted. The simulated effects on some of the regional income component distributions are fairly considerable in regard both to equalizing the distributions and increasing the shares of the poorest. However, the overall effects are regressive in both urban and rural regions."