- Volume 5, Issue 1, 1951
Volume 5, Issue 1, 1951
- Article
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The Action of Streptomycin on Bacterium lactis aerogenes
More LessSUMMARY: The main action of streptomycin on Bacterium lactis aerogenes is bactericidal. In an ‘untrained’ population the number of cells able to survive in streptomycin diminishes with increasing concentration of the antibiotic. If the surviving cells are mutants, many mutant types must be assumed to explain the many degrees of resistance. Ability to survive does not necessarily imply ability to grow in streptomyein. Survivors sometimes have a long lag before growth occurs in liquid or solid media, which suggests that modification of cell protoplasm may be taking place. Colonies picked from high-concentration streptomycin plates often contain so many non-resistant cells that their origin from a single resistant mutant is unlikely. Training to grow in streptomycin may involve a mixed process of selection (by killing) and adaptation. There is close correspondence between the degree of resistance and the training concentration. Partial dependence on streptomycin is acquired. An attempt to train a culture by a method designed to exclude selection was unsuccessful.
Morphological changes were found in untrained cultures grown in streptomycin.
Different samples from one culture frequently showed considerable variation in the number of apparently resistant cells present, depending at least partly on the dilution of the sample and the conditions of spacing on the plate. Resistance is a conditional property; in view of this it is dangerous to construct mutational theories on the evidence of variability between different cultures.
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The Photographic Examination of Giant Colonies
More LessSUMMARY: An apparatus was designed to photograph colonies of micro-organisms on Petri dishes either under conditions of dark-field illumination or of top-lighting. It serves to reveal any motility of the organisms and is valuable as an aid to identification, particularly in the genus Acetobacter, members of which have characteristic giant colonies.
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Formation of Clear Zones with ‘Sensitive’ and ‘Resistant’ Staphylococcus aureus in Penicillin Plate Assays
More LessSUMMARY: The high-power microscopical examination of stained specimens of portions of agar plate cultures of bacteria allows bacterial cells and colonies to be studied in their original positions. The disposition and morphology of bacteria from the edges of clear zones on penicillin assay plates under conditions sufficiently standardized permitted a distinction between sensitive and resistant strains of Staphylococcus aureus. With a sensitive strain ‘ghost zones’ were formed of partially lysed, distorted and abnormally staining cells; with a resistant strain a ‘seatter zone’ was formed of apparently normal cells in isolated colonies:
For plate assay work, a sensitive strain may be used when only low concentrations of the drug are available, a resistant strain may be expected to give a sharper zone edge, but will require higher concentrations to provide an adequate response.
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Classification of Staphylococci by Penicillin Lysis
More LessSUMMARY: In twenty-nine of a series of thirty strains of Staphylococcus aureus and albus there was correspondence between penicillinase production, ‘cell sensitivity’ to penicillin and penicillin lysis, but no relation between these characteristics and the results of eleven routine tests for pigmentation. β-haemolysis, coagulase formation and various biochemical reactions.
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Cell Structure in Relation to the Gram Reaction as Shown During Lysis of Bacillus subtilis
More LessThe cell wall of Bacillus subtilis was shown to lie externally to the Gram-positive staining area of the cell. Conversion of these bacteria to the Gram-negative state, whether natural or induced, did not necessarily result in a decrease in cell size. When a decrease occurred it was correlated with the disappearance of an ‘ectoplasm’ staining area and with the inability of the residual cell substance to be converted to the Gram-positive state with magnesium ribonueleate.
Cell autolysis proceeded as follows. First the cell lost magnesium ribonucleate and was therefore Gram-negative, the ectoplasm and cell wall staining areas were retained, and the cell could be reconverted to the Gram-positive state by exposure to magnesium ribonueleate. The size of the cell was normal. Next, the ectoplasm and cell wall staining areas disappeared. This was correlated with an inability to be re-converted to the Gram-positive state and with a smaller size. Finally, cell autolysis was completed and the cell disappeared.
Gram-negative species were shown to possess an ectoplasm staining area which differed from that of normal Gram-positive cells since it could not be made to stain Gram-positive by exposure to magnesium ribonucleate. The ectoplasm staining area of Gram-positive cells was shown not to be in itself the reason for Gram-positive staining. However, the presence of this area correlated with the cells ability to be reconverted to the Gram-positive state by magnesium ribonucleate, and thus it is probably important in the Gram reaction.
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A Genetic Approach to Variation in Influenza Viruses: 1. The Characters of Three Substrains of Influenza Virus A (WS)
More LessThe three virus types derived from the classical WS strain of influenza virus can be distinguished by a relatively wide range of ‘marker’ characters, which are available for the recognition of virus characteristics in studies of variation and recombination. Despite their common origin the three WS strains have diverged very markedly one from another. Each has unique characteristics: NWS its absence of enzymic and indicator activity, its neurotropism; WSE its firm non-eluting adsorption to red cells; WSM its extremely heat-resistant haemagglutinin. From the point of view of the general pathology of virus infection the neurotropic character imposed on an influenza virus is the most important of the variant qualities.
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A Genetic Approach to Variation in Influenza Viruses: 2. Variation in the Strain NWS on Allantoic Passage
More LessWhen the strain NWS of influenza virus, which is adapted to multiplication in mouse brain, is submitted to allantoic passage in the chick embryo, it maintains its original character if passed at limiting infective dilutions. When passage is made with a low dilution of the same virus preparation the strain changes toward a more normal character. These phenomena are regarded as providing formal proof that the changes are mutational in origin.
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A Genetic Approach to Variation in Influenza Viruses: 3. Recombination of Characters in Influenza Virus Strains Used in Mixed Infections
More LessWhen the non-encephalitogenic strain of influenza virus A, WSM, was mixed with the influenza strain NWS in suitable proportion no encephalitis followed intracerebral injection of the mixture in mice. When the amount of WSM relative to NWS was decreased partial interference resulted and from four mice so inoculated, virus strains referred to as WS-NM were isolated, which appear to be recombinants. The NM strains were encephalitogenic for mice, though in varying degree, their haemagglutinin was almost as resistant to heat inactivation as that of WSM and they had at least one character (position in the receptor gradient) in which they differed from both the original strains.
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A Genetic Approach to Variation in Influenza Viruses: 4. Recombination of Characters Between the Influenza Virus A Strain NWS and Strains of Different Serological Subtypes
More LessMice were inoculated intracerebrally with mixtures of the influenza virus strain NWS and the serologically distinct non-neurotropie strains MEL, OcI and SW. From mouse brains removed about the 5th or 6th day virus strains were obtained which, after at least two passages at limiting infective dilution, showed active encephalitogenic power with the serological character of the second strain of the original mixture. These are regarded as recombinants. The strains in general show in vitro characters close to those of the serologically similar ‘parent’. They have, however, diminished enzymie action on ovomucin and do not readily clute from red cells; in this they resemble the strain NWS. They are more readily converted to the indicator state than either of the original strains.
The process by which these unusual types arise is discussed in the light of recent views that intracellular multiplication of bacterial viruses and of some animaal viruses takes place not by binary fission but by the breaking down of the infective unit into smaller particles which are the replicating units. It is concluded that the recombinants arise by recenstitution of infective particles from the pool of repticating units produced by double infection of a single cell by virus particles of both parent types.
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The Conversion of Certain Soluble Sugars to a Glucosan by Holotrich Ciliates in the Rumen of Sheep
More LessSUMMARY: When in vitro fermentations of glucose, fructose or sucrose are carried out under conditions comparable with those in the rumen by means of relatively small inocula of strained rumen contents from hay-fed sheep, the holotrichously ciliated protozoa which are present store immense numbers of microscopic granules consisting of a practically protein-free glucosan giving a purple colour with iodine. The granules can be liberated by bursting the protozoa by the action of the synthetic detergent Teepol XL under mild conditions. An exactly similar polysaccharide granule preparation car be made from protozoa present in the rumen itself if rumen contents are withdrawn 2–4 hr. after feeding. The yield of iodophilic polysaccharide so obtained may be equivalent to approximately 25% of the weight of water-soluble, yeast-fermentable sugars in a single feed of hay. No granule-filled protozoa are present 9 hr. after feeding.
Other simple sugars such as glucuronolactone, galactose, mannose, xylose, arabinose, aorbose, lactose, cellobiose and maltose, are not markedly converted into polysaccharide granules by rumen protozoa, during in vitro fermentation.
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New Techniques for the Study of Growin? Micro-or?anisms
More LessSUMMARY: A method is described for the examination of growing micro-organisms by vertical and oblique incident illumination using an illuminator of the ‘Universal Illuminator’ (Messrs Cooke, Troughton and Simms) type. A moist chamber has been developed to enable this method to be used for the routine examination of bacterial cultures, and examples are given of both aerobic and anaerobic cultures on the surface of solid nutrient media, preferably containing nigrosine.
This method has also been used for following spore germination of Bacillus subtilis in a liquid medium. A method using Cellophane as a support for growth is also described. Certain organisms can be grown on Cellophane ‘windows’ made in the caps of Bijou bottles containing a liquid medium; this apparatus is suitable for the repeated but not continuous examination of young growths.
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The Application of Electron Microscopy to the Study of Plant Viruses in Unpurified Plant Extracts
More LessSUMMARY: Rods of variable lengths occurred in sap from plants infected with tobacco mosaic, cucumber mosaic, potato X, potato Y, henbane mosaic, tobacco etch, and cabbage blackring viruses; the first two were about 15 mµ. wide and appeared rigid, the others were about 10 mµ. wide and apparently flexible. Sap from plants infected with tomato bushy stunt, tobacco ringspot and two tobacco necrosiss viruses contained spherical particles about 26 mµ. in diameter; two particles, one about 18 mµ. and the other about 37 mµ. in diameter occurred in sap from plants infected with a third tobacco necrosis virus. No specific particles were identified in sap from plants infected with tomato spotted wilt, potato leaf roll, cauliflower mosaic, tomato aspermy, sugar beet mosaic and sugar beet yellows viruses. Serologically related strains of any one virus were morphologically indistinguishable, but this has little diagnostic value because so also were some unrelated viruses.
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Bacteriolysis by a Species of Streptomyces
More LessSUMMARY: The lysis of dead Bacterium coli by concentrates prepared from filtrates of a Streptomyces sp. is probably due to proteolysis. In any event the lysis can be accounted for by proteolysis, even if the action of other bacteriolytic enzymes cannot be excluded. The streptomyces preparation contains at least two proteolytic enzymes, one digesting casein and the other digesting protein(s) present in Bact. coli. The substrates of the autolytie enzymes of Bact. coli are probably different from those of the streptomyces enzymes.
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Virus-like Bodies in the Blood of the House Cricket
More LessSUMMARY: Virus-like structures were accidentally discovered by electron-microscopy in the blood of adult house crickets which had no external signs of disease.
During an examination by electron-microscopy of haemolymph clots of insects, granular bodies were found by chance in preparations from the house cricket (Gryllulus domesticus). These structures are briefly described in the following note.
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The Vitreoscillaceae: A Family of Colourless, Gliding, Filamentous Organisms
More LessSUMMARY: A new family, the Vitreoscillaceae, is proposed for a group of microorganisms which are characterized by their colourless, gliding trichomes. The family has certain affinities with myxobacteria and still more with colourless myxophyceae, especially with the Beggiatoaceae.
Two genera, Vitreoscilla and Microscilla and seven species are described, three species tentatively referred to Vitreoscilla, two to Microscilla, and two other genera are provisionally named.
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The Development of Bacterial Flagella in the Germinatinģ Microcyst
More LessSUMMARY:The microcyst stage of Salmonella typhi, Proteus vulgaris, Bacterium coli and Pseudomonas fluorescens is non-motile and devoid of flagella. Observations by electron- and photomicroscopy indicate that the flagella grow outwards through the cell wall of the germinating microcyst. They commence to develop after about 2 hr. incubation. Alike in bacteria with peritrichous and polar flagelia a single, polar or sub-polar flagellum develops first. In the process of maturation the flagella are shed and the non-motile microeysts produced. Basal granules may occasionally be observed.
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The Development of the Surface Structures in Dividinǵ Bacteria
More LessSUMMARY: The cell wall of growing Gram-negative bacteria is formed mainly, or entirely, at one pole of the cell. At this point the cell wall is soft and transparent to the electron beam, and there is a concentration of stainable material in the underlying cell membrane. A similar ‘growing point’ occurs at the point of cell division. In dividing bacteria, the portion of the surface which bears the flagella is retained in its entirety by one daughter cell, the other daughter cell grows new flagella.
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A Method for Distinģuishinģ Between Viable Spores and Mycelial Fraģments of Actinomycetes in Soils
More LessSUMMARY: When shaken in suspension, vegetative actinomyeete mycelium breaks into a large number of viable fragments which are killed when shanking is prolonged. Spores do not break up into smaller particles and are more resistant to shaking than vegetative fragments. Suspensions of vegetative mycelium may be distinguished from spores by the manner in which the viable count varies with time of shaking. While it is not possible to estimate the numbers of spores and of vegetative particles in mixed suspension the predominating form may be identified. Soil samples from Broadbalk field had a high count of actinomyeetes which were almost certainly present as free spores.
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The Measurement of the Aeration of Culture Media
More LessSUMMARY: The aeration of culture media can be measured in terms of ø L (defined below) which is dependent on rate of air flow, agitation, etc. Two methods of measuring ø L are given, based on the polarographic estimation of dissolved oxygen. For penicillin and streptomycin fermentations there is a correlation between the amount of antibiotic produced and ø L.
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The Serolo?y of Fifty Strains of Proteus vul?aris
More LessSUMMARY: Of fifty strains of Proteus vulgaris from human infections, seven of the ‘vulgaris’ and forty-three of the ‘mirabilis’ fermentative type, forty-four were brought into Belyavin’s phase A. which represents the modal S form of recently-isolated strains, and analysed serologically by their H and O antigens. Three of the six remaining strains were irreversibly R. and three were too unstable antigemcally for the routine analysis.
The antigens determining the somatic O types were resistant to heating at 95°, to ethanol and to dilute HCl, treatments that destroyed the H antigens. Serologically similar O antigens were extracted from the bacilli by hot formamide and by ethanol precipitation of tryptie digests.
As in other recent surveys of Proteus serology, the classification of strains by major O antigens was more clear-cut than by H antigens, though some minor O antigens were distributed differently from the major. The forty-four phase-A strains fell into eighteen O-antigenic types, three of these being the classical OX2, OX19 and OXK types, strains of which were included in the survey. The H antigens of each strain were often apparently multiple. but grouping by major H antigens was broader than by O antigens; moreover. H antigens were often common to strains with dissimilar O antigens.
Apart from the antigenic changes accompanying variation from phase A to phases B or C, there were suggestions of other phasic variations in both H and O antigens, which, if substantiated, may necessitate a reconsideration of serological classifications of the group. The three unstable strains in the collection could not be definitely assigned to any O-antigenie type.
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