Fabrication of one-dimensional CoFe2/C@MoS2 composites as efficient electromagnetic wave absorption materials

New types of electromagnetic (EM) wave absorption materials with a light weight, strong absorption ability and wide absorption frequency have been widely explored. Nevertheless, it is still an intractable challenge to design the structure of the materials and rationalize multiple components. In this work, one-dimensional (1D) CoFe₂/C@MoS₂ composites were prepared via electrospinning technology, high-temperature carbonization and hydrothermal method. SEM and TEM images reveal that the as-prepared CoFe₂/C fibers with a 1D structure are well coated with MoS₂. The excellent absorption performance of the composites is mainly attributed to the 1D structure and the ideal impedance matching. CoFe₂/C@MoS₂ composites show strong absorption ability with an optimal reflection loss (RL) of -66.8 dB (13.28 GHz) at a matching thickness of 2.12 mm. Meanwhile, the composite possesses an effective absorption frequency range between 10.70 and 16.02 GHz with a bandwidth of 5.32 GHz. These results indicate that CoFe₂/C@MoS₂ composites will become promising lightweight and highly efficient MA materials.

Fabrication of one-dimensional ZnFe2O4@carbon@MoS2/FeS2 composites as electromagnetic wave absorber

In this work, one-dimensional (1D) ZnFe₂O₄@carbon@MoS₂/FeS₂ composites were synthesized by hydrothermal method, magnetic-field-induced distillation-precipitation polymerization and high-temperature carbonization. The structure, morphology, composition, magnetic performance and electromagnetic (EM) wave absorbing properties of the composites were systematically studied. The composites show strong microwave absorption (MA) capacity with a minimum reflection loss (RL_min) value of -52.5 dB at 13.2 GHz, and have an effective absorption frequency range of 10.10-15.08 GHz with a bandwidth of 4.98 GHz when the thickness is 2.23 mm. It is expected that as-synthesized 1D ZnFe₂O₄@carbon@MoS₂/FeS₂ composites can be a promising EM wave absorption material.

Microwave absorption enhancement of 2-dimensional CoZn/C@MoS2@PPy composites derived from metal-organic framework

Metal-organic framework (MOF) materials have caused widespread concerns in the field of microwave absorption, due to the unique microstructure and electronic state. Herein, the CoZn/C@MoS₂@polypyrrole (PPy) composites were prepared through MOF self-template method. The MoS₂ sheets and PPy shell incorporated for optimizing impedance matching of two-dimensional (2D) CoZn/C composites. The introduction of MoS₂ sheets and PPy shell endowed the composites with enhanced microwave absorption. The as-prepared CoZn/C@MoS₂@PPy composites showed a minimum reflection loss (RL) of -49.18 dB with the thickness of 1.5 mm. In addition, the effective absorption bandwidth (EAB, RL values exceeding -10 dB) covered 4.56 GHz, which showed greater performances than CoZn/C composites under a lower thickness (<2 mm). This work not only provides a facile route for fabricating MOF-derived carbon-based composites as microwave absorbers, but also broadens the application of MOF materials.

Findings from the first public COVID-19 temporary test centre in Hong Kong

INTRODUCTION

The Hospital Authority of Hong Kong Special Administrative Region established a coronavirus disease 2019 (COVID-19) temporary test centre at the AsiaWorld-Expo from March 2020 to April 2020, which allowed high-risk individuals to undergo early assessment of potential severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. This study reviewed the characteristics and outcomes of individuals who attended the centre for COVID-19 testing.

METHODS

This retrospective cross-sectional study collected epidemiological and clinical data. The primary outcome was a positive or negative SARS-CoV-2 test result, according to reverse transcription polymerase chain reaction analyses of pooled nasopharyngeal and throat swabs collected at the centre. The relationships of clinical characteristics with SARS-CoV-2 positive test results were assessed by multivariable binary logistic regression.

RESULTS

Of 1258 attendees included in the analysis, 86 individuals tested positive for SARS-CoV-2 infection (positivity rate=6.84%; 95% confidence interval [CI]=5.57%-8.37%). Of these 86 individuals, 40 (46.5%) were aged 15 to 24 years and 81 (94.2%) had a history of recent travel. Symptoms were reported by 86.0% and 96.3% of individuals with positive and negative test results, respectively. The clinical characteristics most strongly associated with a positive test result were anosmia (adjusted odds ratio [OR_adj]=8.30; 95% CI=1.12-127.09) and fever OR_adj=1.32; 95% CI=1.02-3.28).

CONCLUSION

The temporary test centre successfully helped identify individuals with COVID-19 who exhibited mild disease symptoms. Healthcare providers should carefully consider the epidemiological and clinical characteristics of COVID-19 to arrange early testing to reduce community spread.

A Jia-shaped artistic patch antenna for dual-band circular polarization

This article presents a novel single-feed circularly polarized patch antenna for dual-band (2.6 and 3.4 GHz) applications. Details of the design procedure and design considerations of the proposed antenna are described. The novelties of the proposed antenna are counted by (i) a meaningful Jia-shaped patch used as the primary radiator; (ii) a 3D L-shaped feeding probe used to excite the stacked patches so that the near degenerate-modes are excited at the desired dual band; (iii) down-tilt beams achieved that are particularly suitable for wall-mount base-stations. The measured 3-dB axial-ratio bandwidths are 2.41-2.61 GHz and 3.25-3.42 GHz, where the maximum gains are recorded as 7.3 and 6.3 dBic, respectively. Methods for the adjustment of band ratio down to 1.18 are discussed. The overall antenna size is 100 × 100 × 12.8 mm³.

Hydronephrosis: Case Report of a Rare Cause of the Supine Hypotensive Syndrome

Hypotension poses a diagnostic challenge to emergency physicians who often have to exclude life-threatening conditions, make correct diagnosis and institute timely treatment. We presented a case of hydronephrosis causing the supine hypotensive syndrome. Management of the supine hypotensive syndrome and the use of emergency bedside ultrasound in evaluating hypotensive patients were discussed.

Sonography of Quadriceps Tendon Ruptures

Quadriceps tendon rupture is an uncommon injury, which may benefit from early operative repair. However, clinical assessment is frequently inaccurate and delayed diagnosis is common. Ultrasound has been shown to be sensitive in detecting quadriceps tendon rupture. We report a case of bilateral quadriceps tendon ruptures diagnosed by ultrasound. Typical sonographic findings were illustrated.

The Use of Ultrasonography in Diagnosing Ruptured Baker'S Cyst in the Emergency Department

Acute calf pain is a common cause of attendance to the emergency department. Deep vein thrombosis and other differential diagnoses can mimic each other. Emergency ultrasonography can help in making the correct diagnosis. We presented a case with initial clinical presentation suspicious of deep vein thrombosis. However, with the use of emergency ultrasonography, a final diagnosis of ruptured Baker's cyst was made in the emergency department.

Sonographic Diagnosis of Rotator Cuff Tears in Anterior Shoulder Dislocation

A 61-year-old gentleman fell from a tree about two meters high and suffered from a right shoulder injury. The physical examination showed tenderness with marked decrease in range of movement over the right shoulder. X-ray of the right shoulder showed anterior dislocation. Closed reduction under sedation was performed. After reduction, ultrasound was done and showed a full-thickness supraspinatus tear. He was referred to the orthopaedic department urgently and an arthroscopic rotator cuff repair was done subsequently.

Ultrasound Assisted Detection and Removal of Wooden Foreign Bodies in Soft Tissue

Soft tissue foreign bodies represent a common cause for emergency department visits. Diagnosis may be difficult especially with non-radiopaque foreign bodies. Undetected wooden foreign bodies can cause significant morbidity, repeat visits, high cost, and extensive surgery. We report a case in which ultrasound was used in the Emergency Department to detect and remove wooden foreign bodies from the soft tissue. Ultrasound and other imaging modalities that may aid in the early diagnosis are discussed.

Left Lower Quadrant Abdominal Mass: A Case of Spigelian Hernia Diagnosed by Emergency Ultrasound

Spigelian hernia is rare. The diagnosis of Spigelian hernia is often challenging. We report a case of Spigelian hernia in which emergency ultrasonography diagnosed correctly a Spigelian hernia, which was later confirmed by computed tomography and at surgery. In our opinion, ultrasonography can be an important tool for emergency physicians in cases of abdominal pain or abdominal mass.

Ultrasound-Guided Foreign Body Removal

A gentleman suffering from right leg penetrating injury presented to a local accident and emergency department. The physical examination did not suggest an embedded foreign body, and he was discharged after local wound dressing. Because of persisting symptoms, he attended another hospital later where an unguided surgical exploration was performed but no foreign body was identified. He was then referred to another hospital, his third one, for further management. The X-ray finding was unremarkable but ultrasound showed a hyperechoic foreign body. Subsequently, ultrasound-guided foreign body removal was performed and a wooden splinter was successfully removed.

Accidental Organophosphate Insecticide Poisoning: a Fatal Child case with Hazards to Emergency Department Staff

A 2-year-old boy was accidentally poisoned by one spoonful of organophosphate insecticide and presented in cardiac arrest. Spontaneous circulation was restored after initial resuscitation and antidote therapy (atropine and pralidoxime) but the boy finally succumbed with multiple complications. We reviewed the literature on the clinical features and management of acute organophosphate poisoning, and the appropriate protective equipment for preventing secondary poisoning of healthcare workers.

Differential Diagnosis of Acute Calf Pain and Swelling with Emergency Ultrasound

Acute calf pain and swelling are common causes of emergency department attendance. Differential diagnoses may mimic each other causing confusion and uncertainty in management. With emergency ultrasound, most of the differential diagnoses for acute calf pain and swelling can be identified with confidence. We present two cases of calf pain and swelling utilising ultrasound to clarify the diagnosis.

Microwave Non-Destructive Inspection and Prediction of Modulus of Rupture and Modulus of Elasticity of Engineered Cementitious Composites (ECCs) Using Dual-Frequency Correlation

This research article presents dual-frequency correlation models for predicting the growth of elasticity and flexural strength of engineered cementitious composites (ECCs) using microwave nondestructive inspection technique. Parallel measurements of microwave properties and mechanical properties of ECC specimens were firstly undertaken in the sense of cross-disciplinary experiments. Regression models were developed via means of nonlinear regression to the measured data. The purpose of the study is: (i) to monitor the flexural strength and elasticity growth; and (ii) to predict their mature values under the influence of different initial water contents, via microwave effective conductance at early ages. It has been demonstrated that both the modulus of rupture (MOR) and modulus of elasticity (MOE) can be accurately modeled and correlated by microwave conductance using exponential functions. The moduli developed as a function of conductance whereas the regression coefficient exhibited a linear relation with water-to-binder ratio. These findings have highlighted the effectiveness of the microwave non-destructive technique in inspecting the variation of liquid phase morphology of ECCs. The dual-frequency correlation can be used for structural health monitoring, which is not only for prediction but also provides a means of verification.

A latent profile analysis on patient empowerment programme in a Hong Kong primary care setting

OBJECTIVE

This study identified the profiles of subgroups of type 2 diabetic (T2DM) patients of the Patient Empowerment Programme (PEP) by different levels of benefits gained in diabetic self-management behaviors, self-efficacy, and health literacy.

METHODS

This study adopted a non-experimental repeated-measures design on T2DM patients who joined PEP, using structured questionnaires. Latent profile analysis (LPA) was used to identify patterns of participants' change on the outcome measures.

RESULTS

Findings of LPA revealed that participants who were older, unemployed, weaker in diabetic self-management, and having a higher self-perception in personal disease risk were more likely to join the empowerment sessions and gained more benefits from the program. Participants with lower impairment in energy function and lower autonomy in personal health care showed more improvement in the outcomes.

CONCLUSION

The study identified significant factors associated with patients' participation on and benefits gained from a service delivery model integrating health education and patient empowerment in a primary care setting.

PRACTICE IMPLICATION

Findings from this study shed light on strategies to improve the PEP design in order to meet the needs of individuals with different health-related profiles.

Patient Empowerment Programme in primary care reduced all-cause mortality and cardiovascular diseases in patients with type 2 diabetes mellitus: a population-based propensity-matched cohort study

AIMS

To assess whether a structured diabetes education programme, the Patient Empowerment Programme (PEP), was associated with a lower risk of first cardiovascular disease (CVD) event and all-cause mortality in a population-based cohort of patients with type 2 diabetes mellitus (T2DM) in primary care.

METHODS

A Chinese cohort of 27 278 patients with T2DM and without previous CVD events on or before the baseline study recruitment date was linked to the Hong Kong administrative database from 2008 to 2013. The PEP was provided to patients with T2DM treated at primary care outpatient clinics through community trained professional educators. PEP non-participants were matched one-to-one with the PEP participants using a propensity score method with respect to their baseline covariates. Cox proportional hazard regression was performed to estimate the associations of the PEP with the occurrence of first CVD event, coronary heart disease, stroke, heart failure and death from any cause, controlling for baseline characteristics.

RESULTS

During a median of 21.5 months follow-up, 795 (352 PEP participants and 443 PEP non-participants) patients experienced a first CVD event. After adjusting for confounding variables, PEP participants had a lower rate of all-cause mortality [hazard ratio (HR) 0.564, 95% confidence interval (CI) 0.445-0.715; p < 0.001], first CVD (HR 0.807, 95% CI 0.696-0.935; p = 0.004) and stroke (HR 0.702; 95% CI 0.569-0.867; p = 0.001) than those without PEP.

CONCLUSIONS

Enrolment in the PEP was associated with lower all-cause mortality and a lower number of first CVD events among patients with T2DM. The CVD benefit of PEP might be attributable to improving metabolic control through empowerment of self-care and the enhancement of quality of diabetes care in primary care.

An Unusual Case of Fever with Purpuric Skin Rash

A 45 years old gentleman with good past health developed on-and-off fever, malaise, bilateral lower limb rash, shortness of breath and palpitation for two weeks. Physical examination showed purpuric skin rash over both lower limbs. The cardiovascular examination showed a pansystolic murmur, best heard at the apex. Bedside echocardiography was performed in the emergency department and revealed vegetation over the mitral valve leaflet with severe mitral regurgitation. He was admitted to the medical ward with a provisional diagnosis of infective endocarditis and subsequently received a mitral valve replacement.

Use of ophthalmic medications during pregnancy

OBJECTIVES

To review potential risks of eye medications to the mother and her foetus.

DATA SOURCES

PubMed search for all relevant articles (1966 to 2003).

STUDY SELECTION

All types of publication that documented potential risks of eye medications during pregnancy. The following key words were used: pregnancy, fetus, teratogenicity, eye, ocular, ophthalmic, glaucoma, antibiotics, anti-inflammatory, and corticosteroids.

DATA EXTRACTION

All relevant articles including original articles, review papers, case studies, and relevant book chapters were extracted and reviewed.

DATA SYNTHESIS

Whether ophthalmic medications can be used during pregnancy is a very important issue; yet, limited information on the subject exists in the literature. Topically applied eye medications that give rise to systemic side-effects are of particular concern to both patients and doctors. Various ophthalmic anti-infective preparations and ophthalmic corticosteroids have shown to cause teratogenicity in animal studies. Furthermore, anti-glaucoma drugs pose potential risks to the foetus if they are absorbed systemically. This article examines the association between the main groups of ophthalmic medication and their possible adverse effects on the mother and the foetus. Recommendations for the treatment of pregnant patients with eye diseases are also discussed.

CONCLUSION

The risk of giving ophthalmic drugs to pregnant women is low. Doctors should be cautious when prescribing drugs for pregnant women and consult experts in the field when in doubt.

Space-filling approach for fast window query on compressed images

Based on the space-filling approach, this paper presents a fast algorithm for window query on compressed images. Given a query window of size n1xn2, the proposed algorithm takes O(n1logT+P) time to perform the window query, where n1=max(n1, n2) and TxT is the image size; P is the number of outputted codes. The proposed algorithm improves the naive algorithm, which needs O(n1n2logT+P) time, significantly. Some experimentations are carried out to demonstrate the computational advantage of the proposed algorithm. From the experimental results, it is observed that the proposed algorithm has about 72-98% time improvement when compared to the naive algorithm.

[The study on the in-vitro stability of Tc(V)-99m dimercaptosuccinic acid]

Tc(V)-99m DMS, developed by Yokoyama et al. in 1981, has been recognized to be advantageous for the scintigraphic diagnosis of various malignant tumors and their metastasis, the aim of this study is to assess the in-vitro stability of Tc(V)-99m DMS. Thin-layer chromatography, including paper chromatography and silica gel thin layer chromatography, is performed to determine the change of radiochemical species presented in the reconstituted solution of Tc(V)-99m DMS prepared from the DMS kit (Institute of Nuclear Energy Research, Atomic Energy Council R.O.C.) and the commercial DMSA kit (Nephroscint, IRE CELLTARG Radiopharmaceuticals Japan). The bioscan imaging scanner is used to measure the Rf value and labeling efficiency of radiochemical species on the chromatographic strip. The in-vitro stability of Tc(V)-99m DMS prepared from the DMS kit and the commercial DMSA kit is studied by examining various parameters which include temperature(degree C) and time(hr) after reconstitution. The results show that the in-vitro stability of Tc(V)-99m DMS prepared from the DMS kit is actually better than that from the commercial DMSA kit. The one-step labeling method of DMS kit is much simpler than the two-step labeling method of DMSA kit.

Task analysis for computer-aided design (CAD) at a keystroke level

The purpose of this research was to develop a new model to describe and predict a computerized task. AutoCAD was utilized as the experimental tool to collect operating procedure and time data at a keystroke level for a computer aided design (CAD) task. Six undergraduate students participated in the experiment. They were required to complete one simple and one complex engineering drawing. A model which characterized the task performance by software commands and predicted task execution time using keystroke-level model operators was proposed and applied to the analysis of the dialogue data. This task parameter model adopted software commands, e.g. LINE, OFFSET in AutoCAD, to describe the function of a task unit and used up to five parameters to indicate the number of keystrokes, chosen function for a command and ways of starting and ending a command. Each task unit in the task parameter model can be replaced by a number of primitive operators as in the keystroke level model to predict the task execution time. The observed task execution times of all task units were found to be highly correlated with the task execution times predicted by the keystroke level model. Therefore, the task parameter model was proved to be a usable analytical tool for evaluating the human-computer interface (HCI).

The E-SCREEN assay as a tool to identify estrogens: an update on estrogenic environmental pollutants

Estrogens are defined by their ability to induce the proliferation of cells of the female genital tract. The wide chemical diversity of estrogenic compounds precludes an accurate prediction of estrogenic activity on the basis of chemical structure. Rodent bioassays are not suited for the large-scale screening of chemicals before their release into the environment because of their cost, complexity, and ethical concerns. The E-SCREEN assay was developed to assess the estrogenicity of environmental chemicals using the proliferative effect of estrogens on their target cells as an end point. This quantitative assay compares the cell number achieved by similar inocula of MCF-7 cells in the absence of estrogens (negative control) and in the presence of 17 beta-estradiol (positive control) and a range of concentrations of chemicals suspected to be estrogenic. Among the compounds tested, several "new" estrogens were found; alkylphenols, phthalates, some PCB congeners and hydroxylated PCBs, and the insecticides dieldrin, endosulfan, and toxaphene were estrogenic by the E-SCREEN assay. In addition, these compounds competed with estradiol for binding to the estrogen receptor and increased the levels of progesterone receptor and pS2 in MCF-7 cells, as expected from estrogen mimics. Recombinant human growth factors (bFGF, EGF, IGF-1) and insulin did not increase in cell yields. The aims of the work summarized in this paper were a) to validate the E-SCREEN assay; b) to screen a variety of chemicals present in the environment to identify those that may be causing reproductive effects in wildlife and humans; c) to assess whether environmental estrogens may act cumulatively; and finally d) to discuss the reliability of this and other assays to screen chemicals for their estrogenicity before they are released into the environment.

The pesticides endosulfan, toxaphene, and dieldrin have estrogenic effects on human estrogen-sensitive cells

Estrogenic pesticides such as DDT and chlordecone generate deleterious reproductive effects. An "in culture" bioassay was used to assess the estrogenicity of several pesticides. The E-screen test uses human breast estrogen-sensitive MCF7 cells and compares the cell yield achieved after 6 days of culture in medium supplemented with 5% charcoal-dextran stripped human serum in the presence (positive control) or absence (negative control) of estradiol and with diverse concentrations of xenobiotics suspected of being estrogenic. Among the organochlorine pesticides tested, toxaphene, dieldrin, and endosulfan had estrogenic properties comparable to those of DDT and chlordecone; the latter are known to be estrogenic in rodent models. The E-screen test also revealed that estrogenic chemicals may act cumulatively; when mixed together they induce estrogenic responses at concentrations lower than those required when each compound is administered alone.

Accuracy and reliability of temperature measurement in the emergency department by instrument and site in children

PURPOSE

1. To determine the accuracy, precision, specificity, sensitivity, positive prediction, and negative prediction of TempaDOT, FirstTEMP, and Genius as compared to the glass mercury thermometer; 2. To determine the influence of age, behavior, febrile status, tympanic membrane bulge, presence of ear wax, and site on temperature readings; and 3. To determine the ability of each instrument to detect a shift in temperature after Tylenol.

METHOD

A quasi-experimental, multiple-correlational design was used to study 960 temperature measurements obtained on 89 febrile and 83 afebrile children in an emergency unit.

FINDINGS

TempaDOT was found to be the most accurate and most precise instrument for children ages 5 years and under with and without fevers. FirstTEMP was found to be most sensitive for temperatures above 37.5 degrees C and best in detecting shifts after Tylenol was given. Age, behavior, febrile status or tympanic membrane bulge did not significantly affect accuracy. The most accurate sites in order of accuracy were: oral axillary, aural, rectal. The order of precision of sites was: oral, aural, rectal, and axillary. Behavior did not significantly affect the precision.

CONCLUSION

TempaDOT was found to be the most clinically useful temperature measurement instrument. FirstTEMP may be used as a screening tool to determine if antipyretic medication is working to decrease fevers. TempaDOT is recommended for use in emergency units to validate the presence or absence of fevers in children especially when the FirstTEMP reading is near 37.0-38.8 degrees C.

A three-year clinical comparison of a sodium monofluorophosphate dentifrice with sodium fluoride dentifrices on dental caries in children

This study compared the anticaries effects of these three fluoride-containing dentifrices: 1100 ppm F as NaF (positive control); 2800 ppm F as SMFP; and 2800 ppm F as NaF. The group using the 2800 SMFP dentifrice showed no significant differences in DMFS or DMFT, compared to the positive control, at anytime during the study. This indicated that higher levels of sodium monofluorophosphate in a dentifrice offer no advantage in caries protection over the conventional level of sodium fluoride, 1100 ppm F.

Analysis of a mutant of Autographa california nuclear polyhedrosis virus with a defect in the morphogenesis of the occlusion body macromolecular lattice

A mutant (m-29) of Autographa californica nuclear polyhedrosis virus (AcMNPV) grew in Spodoptera frugiperda and Trichoplusia ni cells but did not form typical intranuclear occlusion bodies (OB); instead, small particles (95 to 180 nm diam.) were produced in copious amounts within nuclei. Ultrastructural studies showed that the particles did not occlude enveloped nucleocapsids and that they lacked a macromolecular paracrystalline lattice and a structure equivalent to the occlusion body envelope. The particles within nuclei stained in an immunofluorescence test with antipolyhedrin antibody and when extracted from cells the major polypeptide of a particle preparation was indistinguishable from polyhedrin when examined on SDS--polyacrylamide gels and had an identical peptide pattern following proteolysis with V8 protease. Other elements believed to be implicated in OB morphogenesis such as a proliferation of intranuclear membranes, enveloped bundles of nucleocapsids, patches of fibrous material and fibrous sheets were present in normal amounts. No alteration in the synthesis or processing of polypeptides was seen in mutant-infected cells. Analysis of m-29 DNA with BamHI, EcoRI and HindIII restriction endonucleases revealed that the HindIII restriction site at the F/V junction of viral DNA was absent in the mutant. No other modifications in the restriction patterns were detected. It is proposed that an alteration in the amino acid sequence of polyhedrin towards the--NH2 terminus of the polypeptide may account for the growth characteristics of the mutant.

Effects of hemolymph from immune and non-immune larvae of Galleria mellonella on the ultra-structure of Pseudomonas aeruginosa

The ultrastructure of Pseudomonas aeruginosa, a pathogen of Galleria mellonella is rapidly altered after in vitro exposure to the hemolymph of vaccinated larvae. The bacteria were treated with normal and immune hemolymph for periods of time ranging from 7 to 28 min at 28 degrees C. In contrast to the apparent non-damaging effects of normal hemolymph, the immune hemolymph caused progressive damage to the cells within 7 min. The initial attack was directed towards the cell wall. Complete degradation was observed after 14 to 28 min exposure to the immune hemolymph.

The effect of rifampicin on the developmental phases of germinating spores of Clostridum sp., MSp+

The effect of rifampicin on the developmental phases of germinating spores of Clostridium botulinum, MSp+, has been studied. At sublethal concentrations of rifampicin (0.05 ng/ml) the time periods required for outgrowth and vegetative growth was significantly prolonged because of the inhibition of RNA and protein synthesis. However, rifampicin had essentially no effect on DNA synthesis or on subsequent spore formation. Chemical analyses showed that the amount of protein present in vegetative cells of the rifampicin-treated cultures was twice as great as in the untreated cultures but the total protein content of endospores was the same in both cases. It was revealed in ultrastructural studies of rifampicin (0.1 ng/ml) treated cultures, examined after 22 h, that septum formation and normal cell division of the emerging cell was blocked and a few cells showed constriction which produced one normal and one protoplast-like daughter cell.

The effect of sublethal doses of rifampin on the sporulation of Clostridium botulinum

Sublethal doses of rifampin (0-005 mug/ml), added to vegetatively growing cultures of a sporogenic mutant of Clostridium botulinum at inoculation time or after 4 h, resulted in a decrease of growth and in blockage of spore formation. But when rifampin was added 6 to 24 h after inoculation, normal growth and sporulation occurred, indicating that the time of addition was critical and that rifampin was most effective on rapidly dividing, exponential-phase cells. Ultrastructural studies showed that when rifampin was added at the time of inoculation, endospore development was blocked at stage III. During subsequent incubation (greater than 10 h) the cells lost their rigidity, and lysis of the mother cell was followed by that of the forespore. When the cultures were treated with rifampin at 4 h, about 40% of the cells were blocked at stage III and about 60% reached stages IV and V. Some showed excessive elongation and contained developing spores at each pole. They appeared to be derived from two daughter cells unable to form a division septum because of a specific inhibitory effect of rifampin on division. It would seem, therefore, that two daughter cells which are genetically coded to form endospores will do so irrespective of the development of a division septum, and the spores are formed at the 'old' polar regions.

Minicell formation in chloramphenicol-treated Bacillus cereus

Bacillus cereus incubated in a synthetic medium containing chloramphenicol, 19 μg/ml, a concentration which is slightly below the minimal inhibitory level, was observed to form from one to several minicells through a series of cytological changes including septum initiation, invagination and completion at the subpolar region of the cell, rupture of the peripheral cell wall along the circumferential path of this region, and finally cell separation. The minicells are spherical or spheroidal in shape. A small number of heart-shaped cells was also seen.

Ultrastructure and characterization of an asporogenic mutant of Clostridium botulinum type E

The asporogenic mutant, RSpoIIIa, showed septum formation and a nearly completed forespore about 4 h after onset of sporulation. The cells show defects at a few sites of the forespore membrane, an absence of 'germ cell wall,' and within 8 h lysis of the cytoplasm occurred indicating that the mutant was blocked at stage III. Some aberrant envelopes were seen later. Lysis of the asporogenic mutant was inhibited for up to 36 h by the addition of 2.4% glucose or sucrose to the medium and 80% of the cells showed septum formation. A comparison of the phenotypic characteristics of the asporogenic RSpoIIIa and the sporogenic MSp+ mutants, as well as the wild type, showed the same ultrastructural changes during the development of the forespore with the accumulation of intracellular iodophilic granules. In addition, the mutants showed specific immunofluorescence and precipitin lines of identity with antisera against the wild-type strain, but unlike the toxigenic wild type, the mutants were nontoxigenic by mouse pathogenicity tests.

Influence of cell-wall thickness on cell division: electron microscopic study with Bacillus cereus

Bacillus cereus that had been exposed to chloramphenicol for 0 and 90 min synthesized walls whose thickness increased with time. These cells were washed and resuspended in fresh growth medium. Cell division was examined by electron microscopy. In untreated cells, a slight invagination of the cytoplasmic membrane with deposit of cross-wall material marked the onset of cell division. The cross wall grew inward until the septum was about [Formula: see text] completed. This was followed by splitting and bifurcation of the outer edge of the cross wall, which in turn separated the peripheral wall scars. Cross-wall penetration with further splitting continued until the daughter cells were completely partitioned. The peripheral wall scars that were located at the junction of peripheral and end walls at the time of cell separation indicated that the zone of cell division was probably not a region of active cell elongation. In cells treated with chloramphenicol for 90 min, cross-wall initiation and completion all occurred beneath a thickened peripheral wall. The circumferential portion of the peripheral wall at the zone of cell division appeared to be responsible for the hindrance of cell separation. This thick layer subsequently severed at three or four sites to allow the separation of daughter cells. For cells that had initiated cross-wall invagination at the time when chloramphenicol was added, accumulation of a large amount of cross-wall material at the zone of cell division was observed. Upon removal of the antibiotic, cells abandoned the old and initiated a new dividing site. For cells that had already completed cross-wall formation at the time of chloramphenicol treatment, the increase in wall thickness did not appear to interfere with cell separation. Models for the different stages of cell division in all these bacteria were presented.

Structural changes associated with extraction of group E spore antigen of Clostridium botulinum

Spores of type E Beluga strain of Clostridium botulinum, which were hydrolyzed with HCl to remove the spore-specific antigen, showed a spore coat which was thinner and projected into the exosporium with multiple protuberances. The changes observed suggest that the antigen is a component of the spore coat connected with the maintenance of rigidity.

Thickened cell walls of Bacillus cereus grown in the presence of chloramphenicol: their fate during cell growth

Bacillus cereus incubated for 4 h in a synthetic medium containing chloramphenicol was observed to form cell walls 2 to 3 times as thick as those from control cells growing in the same medium containing no antibiotic. Then the cells were washed and reincubated in fresh synthetic medium and the ultra-structural changes in the thickened walls during cell growth and elongation were examined by electron microscopy. After incubation for 20 min, multiple ruptured sites and internal fractures appeared randomly on the surface of the thickened cell wall. Large and small pieces of thickened wall fragments soon "peeled off" from the surface, leaving behind a deeper layer of wall material. Normal cell growth and elongation resumed after partial removal of the thickened cell wall. After several generations, thickened wall fragments were not observed on the surface of daughter cells.

Autoradiographic studies of bacterial cell wall replication. I. Cell wall growth of Bacillus cereus in the presence of chloramphenicol

The pattern of cell wall synthesis as measured by the incorporation of tritiated alanine into the cell wall of Bacillus cereus, and the number of synthesizing sites in the cell wall were studied by the direct and the reverse autoradiographic labelling methods.In the absence of chloramphenicol, the new cell wall was initiated at two or three segments, and later increased to four or five segments which continued to elongate but not to increase in number until the bacilli had made preparation for cell division. Shortly before the centripetal growth of the cell wall and constriction to separate daughter cells, two to three more new wall-segments were added to those already present. The second and third generation cells retained some old wall-segments from the first-generation mother, which remained as discrete clusters of grains, and could easily be distinguished from the new segments.In the presence of chloramphenicol, the new wall was initiated at 8 to 10 sites. Further incubation resulted in the uniform incorporation of labels at multiple sites along the entire cell length.The patterns of new wall replication as studied by the two methods were compared. To account for the difference in synthesizing sites when chloramphenicol is present, it is suggested that the cells have either used the maximum number of sites or have completely bypassed all the sites and allowed the tritiated alanine to diffuse into the wall to become incorporated.

Cell wall replication in Saccharomyces cerevisiae

Cell wall growth and bud formation in Saccharomyces cerevisiae was studied by labelling with fluorescent antibody. Labelled cells were grown in a glucose yeast extract broth and examined at 15-min intervals. The new cell wall was largely non-fluorescent while the old wall showed no reduction of fluorescence during growth of the bud. Bud formation was initiated as a small bulge on the cell wall, and further increase in size was accompanied by the formation of a constriction around the basal end which led to the separation of the bud from the mother yeast cell. The actively growing area of the bud was an annular band close to the base. It appears that the cell wall of the bud was, almost entirely, newly synthesized and contained very little old cell wall material. The process of wall synthesis is compared with the pattern found in several bacteria and with what is known of the process in other fungi.