摘要:

The extension of bundles of bacterial cellulose microfibrils on agar surfaces was investigated using pseudoreplicas in the electron microscope. Two classes of bundles were distinguishable; those which were composed of many short individual microfibrils of nearly uniform length (1–3 μ) and those in which there were only a few long microfibrils (> 50 μ). The growth pattern of single straight cellulose microfibrils, the proportion of bundles containing many short microfibrils and the extent of coiling of microfibrils were influenced strongly by the sample of agar used to form the surface. These observations are consistent with the suggestion that the mode of extension of bacterial cellulose microfibrils is sensitive to the concentration of an extracellular precursor in small pools on the agar surface.

ISSN:0008-4166    

DOI:10.1139/m68-016

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

In an attempt to find a suitable medium for determining the ability of psychrophilic bacteria and yeasts to grow at subzero temperatures, six antifreeze compounds were added individually and in combination to Trypticase soy broth and agar. The media were tested for their ability to support good growth of psychrophilic bacteria at 20 °C and to resist freezing at subzero temperatures. In general, media which supported good growth at 20 °C froze at −7 °C, whereas media which did not freeze at −7 °C did not support good growth at 20 °C. In supercooled liquid media, however, three species ofBacillusgrew at −2 °C, one at −4.5 °C, and five at −5 to −7 °C. Generation times were approximately 4 days at −2 °C, 7 days at −4.5 °C, and 9 to 11 days at −5 to −7 °C. On supercooled growth-supporting agar media, two Gram-positive cocci, one Gram-negative rod, and four species of yeast grew at −2 °C. The latter also grew at −4.5 °C. Three species ofBacillusgrew at −7 °C, and two at −10 °C.

ISSN:0008-4166    

DOI:10.1139/m68-017

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

It has been shown that cytoplasm-modifying antibodies as demonstrated by the Sabin–Feldman dye test were elicited in the guinea pig after inoculation of phenol-killed toxoplasma organisms and that the addition of an adjuvant to the suspension induced immunity to reinfection in the animals. Protection from reinfection was also provided by recovery from laboratory-induced infection.Passive immunity studies were conducted using pooled antiserum from actively immunized guinea pigs. A slight increase in average survival time was shown in mice when the sera were used. The exception was in the case of serum from guinea pigs injected with an aqueous suspension of phenol-killed organisms. When "accessory factor" was incorporated with these antisera there was an additional increase in survival time in mice, but this increase was not statistically significant in every case.It was shown that neither vaccination nor recovery from experimental infection, even in the presence of very high titers of dye test antibodies, completely prevented the persistence of toxoplasma in various organs of the guinea pigs which had been challenged.

ISSN:0008-4166    

DOI:10.1139/m68-018

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Griseofulvin had no effect on the respiration ofBotrytis cinereabut, nevertheless, inhibited growth and caused abnormal hyphal formations, including stunting, spiraling, thickening of the cell wall, and disorientation of growth. Treated cells had an increase in total deoxyribonucleic acid and phosphorus but not in protein, carbohydrate, lipid, and ribonucleic acid. Griseofulvin-treated cells synthesized DNA from labelled glucose and glycine continuously and for much longer periods than control cells so that their total DNA content was greater than that in untreated cells. However, the antibiotic allowed slightly less incorporation with aspartic acid -U-14C as the precursor than the controls. Griseofulvin caused 25 to 50% increased incorporation of carbon into RNA from glucose and glycine but the increases were not due to a prolongation of the synthetic period, and again aspartic acid incorporation was slightly decreased. Griseofulvin was bound to the particulate parts of the cell and was especially high in the lipid fraction of the cell. The antibiotic was not bound to DNA or to RNA.

ISSN:0008-4166    

DOI:10.1139/m68-019

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Comparative studies have been made of the extracellular release of coxsackievirus B5 from HEp-2 cells. The latter were maintained as monolayers or as freshly trypsinized cells, kept either in suspension or allowed to settle out. In accordance with some workers we have found that the suspended cells release virus earlier and in larger amounts than monolayer cells. We attribute and attempt to show experimentally that this difference, to a large degree, is the result of the physically round shape of the suspended cell as compared to the varied shape of the monolayer cell.

ISSN:0008-4166    

DOI:10.1139/m68-020

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Ukauwa virus, a Bunyamwera group arbovirus endemic in the Ethiopian zoogeographic region, multiplied in the tissues of North American mosquito speciesAedes canadensis(Theobald) andAedes triseriatus(Say) after intrathoracic inoculation. This virus also multiplied in laboratory-bredAedes aegypti(L.) after both feeding and injection. Ukauwa virus now fulfills the biological criteria of an arbovirus. In these three mosquito species, after initial detection of infective virus immediately after inoculation, an eclipse phase with lack of detection of infectivity was observed 6 hours later, and was followed by initial recovery of virus (1.0 log mouse LD50) at 12 hours and thereafter steady virus increments in thorax, salivary glands, gut, and legs which reached maximum titers of 5.4 to 6.3 log mouse LD50in 4 days. InA.aegyptifed Ukauwa virus no infectivity was detected during the first 8 days after the meal. After initial detection of infective virus (3.0 log mouse LD50) on day 10, maximum titers of 4.3 to 5.3 log mouse LD50were reached 4 days later.A.aegyptitransmitted Ukauwa virus to weaned mice on the 12th and 14th days after an infective blood meal, when virus titers in the salivary glands exceeded 4.3 log mouse LD50. The infection threshold of Ukauwa virus forA.aegyptiby feeding was 4.7 log mouse LD50per 0.002 ml.

ISSN:0008-4166    

DOI:10.1139/m68-021

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

1.A wide range of fungi have been isolated from foodstuffs, and their ability to produce aflatoxins and, in some instances, ochratoxin A, was determined. Specimens were obtained from households (including samples associated with illness), from retail stores, and from processing plants. Of 128 fungi, isolated from 74 food samples, and cultured on complex media and on shredded wheat, 16 were found to produce toxins. Alfatoxins were produced not only byAspergillus flavusisolates but also by aRhizopussp. and anAspergillus ochraceus. Six strains identified asAspergillus flavusvar.columnarisformed aflatoxin B2only. Ochratoxin A was produced by aPenicilliumsp. as well as byA.ochraceusisolates.

ISSN:0008-4166    

DOI:10.1139/m68-022

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

In this investigation,Aerobacter cloacaeis shown to inactivate cephalosporin by hydrolysis of its beta-lactam ring. This was demonstrated by iodine absorption and infrared absorption spectra.The values of the Michaelis constant obtained with cephalosporin C and deacetyl cephalosporin C indicate a great affinity of theAerobacter'sbeta-lactamase for its substrate. The enzyme was most active at pH 7.0 and 37 C. Aqueous washings of theAerobactercells were a potent source of enzyme.The beta-lactamase ofA.cloacaewas active on both cephalosporin and penicillin. A higher rate of hydrolysis was observed with cephalosporin C and deacetyl cephalosporin C than with cephalothin and cephaloridine. The ratio of reaction rates on cephalosporin C to that on penicillin G was consistently of the order of 100 to 1. The activity on V, N, and especially the semisynthetic penicillins was also low.TheA.cloacaeenzyme was easily demonstrable in large amount without added inducer. By contrast, the activity of the beta-lactamase fromPseudomonas pyocyaneacannot be detected unless high concentrations of inducer are used.

ISSN:0008-4166    

DOI:10.1139/m68-023

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Pertussis sonic lysates were adjusted to a series of pH values between 3.0 and 11.0, held for 1 hour at room temperature, and then returned to neutrality and assayed for residual mouse protective antigen (MPA) and histamine-sensitizing factor (HSF) activities. The percentage in-activation of MPA at pH 3.0, 10.0, and 11.0 was respectively 30, 18, and 40 but only the last value is significantly different from the pH 7.2 control. The percentage inactivation of HSF in the same samples was 40, 29, and 75 respectively. Exposure to pH 11.0 had a significantly greater destructive effect on HSF than on MPA.These data may be of future value in helping to develop methods for purifying MPA, for they indicate that this factor is reasonably stable to pH within a usefully wide range.

ISSN:0008-4166    

DOI:10.1139/m68-024

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Semliki Forest virus from brains of infected suckling mouse was separated by cesium chloride equilibrium density gradient centrifugation into two fractions, both able to agglutinate red blood cells of goose. The heavy fraction (HF density 1.24) had more infectivity, had a sedimentation coefficient of 285 S, and contained intact virus particles, diameter about 75 mμ. The light fraction (LF density 1.205) of equivalent HA (hemagglutinating activity), had less than 1% of the infectivity of the HF and did not contain intact virus particles. It consisted of "empty" virus particles and fragments of the fragile envelope material. The complete virus particle consists of an envelope of complex character surrounding a well-defined core. Shadow-cast preparations of HF show pointed and truncated shadows which suggest cubical symmetry, and the core of full particles, in thin sections, shows an angular, often pentagonal or hexagonal configuration. This suggests that the cubical symmetry of the full particle depends upon the fundamental symmetry of the core, which appears to be icosahedral.

ISSN:0008-4166    

DOI:10.1139/m68-025

出版商:NRC Research Press    

年代:1968

数据来源: NRC