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Biomedical subjects

W Meijer

Publications and source records attributed to W Meijer.

7 recordsLinked to original sources
PubMed2001

Fluorescent method for monitoring cheese starter permeabilization and lysis.

A fluorescence method to monitor lysis of cheese starter bacteria using dual staining with the LIVE/DEAD BacLight bacterial viability kit is described. This kit combines membrane-permeant green fluorescent nucleic acid dye SYTO 9 and membrane-impermeant red fluorescent nucleic acid dye propidium iodide (PI), staining damaged membrane cells fluorescent red and intact cells fluorescent green. For evaluation of the fluorescence method, cells of Lactococcus lactis MG1363 were incubated under different conditions and subsequently labeled with SYTO 9 and PI and analyzed by flow cytometry and epifluorescence microscopy. Lysis was induced by treatment with cell wall-hydrolyzing enzyme mutanolysin. Cheese conditions were mimicked by incubating cells in a buffer with high protein, potassium, and magnesium, which stabilizes the cells. Under nonstabilizing conditions a high concentration of mutanolysin caused complete disruption of the cells. This resulted in a decrease in the total number of cells and release of cytoplasmic enzyme lactate dehydrogenase. In the stabilizing buffer, mutanolysin caused membrane damage as well but the cells disintegrated at a much lower rate. Stabilizing buffer supported permeabilized cells, as indicated by a high number of PI-labeled cells. In addition, permeable cells did not release intracellular aminopeptidase N, but increased enzyme activity was observed with the externally added and nonpermeable peptide substrate lysyl-p-nitroanilide. Finally, with these stains and confocal scanning laser microscopy the permeabilization of starter cells in cheese could be analyzed.

Cell Membrane Permeability↗
PubMed1998

Lysis of Lactococcus lactis subsp. cremoris SK110 and its nisin-immune transconjugant in relation to flavor development in cheese.

To develop a nisin-producing cheese starter, Lactococcus lactis subsp. cremoris SK110 was conjugated with transposon Tn5276-NI, which codes for nisin immunity but not for nisin production. Cheese made with transconjugant SK110::Tn5276-NI as the starter was bitter. The muropeptide of the transconjugant contained a significantly greater amount of tetrapeptides than the muropeptide of strain SK110, which could have decreased the susceptibility of the cells to lysis and thereby the release of intracellular debittering enzymes.

Bacteriolysis↗
PubMed1996

'Burnout' among Dutch midwives.

OBJECTIVE: to determine the effect of workload on 'burnout' having considered work capacity. DESIGN: cross-sectional study. SETTING: Dutch community midwives in independent practice. PARTICIPANTS: 200 Dutch community midwives. MEASUREMENTS: three-week diary recordings, a questionnaire on practice and personal characteristics, and a questionnaire on 'burnout', social support and coping style. FINDINGS: differences in 'burnout' can be explained partly by the midwife's workload and partly by her work capacity. A high workload may lead to 'burnout' when a midwife is unable to handle stressful situations. KEY CONCLUSIONS: when a higher percentage of the supervised births occurred at the client's own home instead of during a short-stay hospital visit, the chances of 'burnout' are lower. IMPLICATIONS FOR PRACTICE: changes in the organisation of Dutch community midwifery care may contribute to the reduction of 'burnout'. 'Burnout' is a complex phenomenon influenced both by individual and organisational factors. When formulating policy to reduce 'burnout' among midwives specific work-related factors must be considered and emphasis be placed on the importance of personal resources.

Adaptation, Psychological↗
PubMed1996

Home births in The Netherlands: midwifery-related factors of influence.

OBJECTIVE: identification of midwifery-related factors influencing the varied percentage of home births in the practice of Dutch midwives. DESIGN: cross-sectional study. SETTING: independent midwifery practices in the Netherlands. PARTICIPANTS: 115 independent midwives. MEASUREMENTS: recordings of time spent on professional activities over three weeks. Questionnaires were completed on practice characteristics and opinion regarding the place and risks of birth. FINDINGS: attending home births is no more time consuming for midwives than assisting at short-stay hospital births. The percentage of home births in a practice is not related to the average number of hours worked per week, nor to the size or type of practice. The percentage of home births is lowest in major cities. Midwives who think more positively about home births and do not consider these to involve greater risks assist at more home births. IMPLICATIONS FOR PRACTICE: the assumption that a heavy workload will interfere with the policy of de-medicalising birth is found to be false. The opinion of a midwife about the desirability and safety of home confinement has a slight positive effect on the percentage of home births in her practice. Those attempting to promote an increase in births at home must take these factors into account.

Attitude of Health Personnel↗
PubMed1996

Regulation of Proteolytic Enzyme Activity in Lactococcus lactis.

Two different Lactococcus lactis host strains, L. lactis subsp. lactis MG1363 and L. lactis subsp. cremoris SK1128, both containing plasmid pNZ521, which encodes the extracellular serine proteinase (PrtP) from strain SK110, were used to study the medium and growth-rate-dependent activity of three different enzymes involved in the proteolytic system of lactococci. The activity levels of PrtP and both the intracellular aminopeptidase PepN and the X-prolyl-dipeptidyl aminopeptidase PepXP were studied during batch and continuous cultivation. In both strains, the PrtP activity level was regulated by the peptide content of the medium. The highest activity level was found during growth in milk, and the lowest level was found during growth in the peptide-rich laboratory medium M17. Regulation of the intracellular peptidase activity appeared to be a strain-dependent phenomenon. In cells of strain MG1363, the activity levels of PepN and PepXP were regulated in a similar way to that observed for PrtP. In cells of strain SK1128, the levels of both peptidases were not significantly influenced by the peptide content of the medium. The presence of specific concentrations of the dipeptide prolylleucine could mimic the low activity levels of the regulated proteolytic enzymes, even to the activity level found on M17 medium. The effect of the presence of the dipeptide prolylleucine in the medium on the activity level of the regulated proteolytic enzymes was confirmed at fixed growth rates in chemostat cultures.

Journal Article↗
PubMed1995

Medium-dependent regulation of proteinase gene expression in Lactococcus lactis: control of transcription initiation by specific dipeptides.

Transcriptional gene fusions with the Escherichia coli beta-glucuronidase gene (gusA) were used to study the medium- and growth-dependent expression of the divergently transcribed genes involved in proteinase production (prtP and prtM) of Lactococcus lactis SK11. The results show that both the prtP and prtM genes are controlled at the transcriptional level by the peptide content of the medium and, to a lesser extent, by the growth rate. A more than 10-fold regulation in beta-glucuronidase activity was observed for both prtP and prtM promoters in batch and continuous cultures. The level of expression of the prtP and prtM promoters was high in whey permeate medium with relatively low concentrations of peptides, whereas at increased concentrations the expression of the promoters was repressed. The lowest level of expression was observed in peptide- and amino acid-rich laboratory media, such as glucose-M17 and MRS. The addition of specific dipeptides, such as leucylproline and prolylleucine, to the growth medium negatively affected the expression of the prtP-gusA fusions. The repression by dipeptides was not observed in mutants defective in the uptake of di-tripeptides, indicating that the internal concentration of dipeptides or derivatives is important in the regulation of proteinase production.

Bacterial Proteins↗